Andres Spicher

Spicher, A., L. B. N. Clausen, W. J. Miloch, V. Lofstad, Y. Jin, and J. I. Moen (2017), Interhemispheric study of polar cap patch occurrence based on Swarm in situ data, J. Geophys. Res. Space Physics, 122, 3837–3851, doi:10.1002/2016JA023750.

Spicher, A., A. A. Ilyasov, W. J. Miloch, A. A. Chernyshov, L. B. N. Clausen, J. I. Moen, T. Abe, and Y. Saito (2016), Reverse flow events and small-scale effects in the cusp ionosphere, J. Geophys. Res. Space Physics, 121, doi:10.1002/2016JA022999.

Spicher, A., W. J. Miloch, L. B. N. Clausen, and J. I. Moen (2015), Plasma turbulence and coherent structures in the polar cap observed by the ICI-2 sounding rocket, J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021634.

A. Spicher, T. Cameron, E. M. Grono, K. N. Yakymenko, S. C. Buchert, L. B. N. Clausen, D. J. Knudsen, K. A. McWilliams J. I. Moen, Observation of Polar Cap Patches and Calculation of Gradient Drift Instability Growth Times: A Swarm Case Study, Geophys. Res. Letters, 2015 DOI: 10.1002/2014GL062590 (in press, accepted 18 Dec 2014

Spicher, Andres; Miloch, Wojciech Jacek & Moen, Jøran Idar (2014). Direct evidence of double-slope power spectra in the high-latitude ionospheric plasma. Geophysical Research Letters.  ISSN 0094-8276.  41, s 1406- 1412 . doi: 10.1002/2014GL059214Plas

• Frøystein, Ingeborg; Spicher, Andres & Oksavik, Kjellmar (2026). Spatial characteristics of the dayside auroral ionosphere observed by Incoherent Scatter Radar. Annales Geophysicae. ISSN 0992-7689. 44(1), p. 577–593. doi: 10.5194/angeo-44-577-2026. Full text in Research Archive Show summary

  Observation-based characteristics of the dayside ionosphere are important for the knowledge of the coupling between the solar wind, magnetosphere and ionosphere. Therefore, this paper presents descriptions and quantitative analyses of characteristics of the polar dayside ionosphere during the winter. We use EISCAT Svalbard radar (ESR) fast elevation scans to obtain both altitudinal and latitudinal information of the ionospheric parameters electron density Ne, electron temperature Te, and ion temperature Ti. We determine the location of the open-closed field line boundary (OCB) and divide the ionosphere into three regions based on their position relative to the OCB: on closed field lines, along the OCB, and in the polar cap. We first show two case examples, illustrative of the method and the dynamic response of the ionosphere to variable solar wind. We then statistically investigate how the parameters vary from closed to open field lines across the OCB and with altitude in the three regions. Finally, we compare the obtained OCB latitudes with the ones obtained in previous studies. Overall, significant differences in the ionospheric parameters can be seen between the three latitude regions. In general, observed enhancements in Te peak in the F-region on open field lines just poleward of the OCB, reaching up to 4° poleward. In particular, Te is highest between 11:00–13:00 MLT where the ESR is most likely below the cusp. During this interval, the gradient in Te from closed to open field lines peaks. Additionally, Ne appears to be slightly enhanced poleward of the OCB at most altitudes and maximizes just below 300 km on open field lines, increasing with a factor 1.2 from closed field lines. In the E-region, Ne decreases with increasing latitude into the polar cap, especially pre-noon. Further, we observe that the ratio between Ne in the E and F regions is larger on closed than on open field lines. In addition, the variability in the ion temperature Ti appears to be larger on open field lines. Together, these result contribute to a quantification of characteristics of the dayside auroral ionosphere with respect to both altitude and latitude.

• Rexer, Theresa; Gustavsson, Björn Johan; Vierinen, Juha; Spicher, Andres; Huyghebaert, Devin Ray & Kvammen, Andreas [Show all 8 contributors for this article] (2026). Improving the Magic constant-data-based calibration of phased array radars. Geoscientific Instrumentation, Methods and Data Systems. ISSN 2193-0856. 15(1), p. 127–139. doi: 10.5194/gi-15-127-2026. Full text in Research Archive Show summary

  We present a method for improved calibration of multi-point electron density measurements from incoherent scatter radars (ISR). It is based on the well-established Flatfield correction method used in imaging and photography, where we exploit the similarity between independent measurements in separate pixels in an image sensor and multi-beam radar measurements. Applying this correction method adds to the current efforts of estimating the magic constant or system constant made for the calibration of multi-point radars, increasing data quality and usability by correcting for variable, unaccounted, and unpredictable variations in system gain. This second-level calibration is especially valuable for studies of plasma patches, irregularities, turbulence, and other research where inter-beam changes and fluctuations of electron density are of interest. The method is strictly based on electron density data measured by the individual radar and requires no external input. This is of particular interest when independent measurements of electron densities for calibration are available only in one pointing direction or not at all. A correction factor is estimated, which is subsequently used to scale the electron density measurements of a multi-beam ISR experiment run on a phased array radar such as RISR-N, RISR-C, PFISR, or the future EISCAT3D radar. This procedure could improve overall data quality if used as part of the data-processing chain for multi-beam ISRs, both for existing data and for future experiments on new multi-beam radars.

• Gavazzi, Etienne; Spicher, Andres; Gustavsson, Björn Johan; Clemmons, James; Pfaff, Robert & Rowland, Douglas (2026). Time-dependent modeling of Alfvénic precipitation observed in the ionosphere. Annales Geophysicae. ISSN 0992-7689. 44(1), p. 1–15. doi: 10.5194/angeo-44-1-2026. Full text in Research Archive Show summary

  Small scale dynamic auroras are generally related with dispersive Alfvén waves. Due to the short spatial and time scales involved, investigating the effects of this type of auroral precipitation on the ionosphere is challenging. In this study, we address this challenge by introducing a recently developed and improved time-dependent electron transport code entitled AURORA. We use high-resolution data from the Visualizing Ion Outflow via Neutral Atom Sensing-2 (VISIONS-2) sounding rocket campaign as input for the modeling. The rocket flew through the active dayside auroral region and the onboard instrumentation measured signatures of Alfvénic precipitation varying on sub-second timescales. With the code, we model the propagation of the electron flux in the ionosphere and we provide a first-order validation for the case studied here. We then present two examples illustrating the modeling capabilities by showing ionization and optical emission rates for Alfvénic and quasi mono-energetic precipitation with similar downward energy flux. The model results show variations in the height of maximum ionization from about 120 to 180 km in less than 0.3 s for the Alfvén case, while it remains stable at about 160 km for the quasi mono-energetic case. Additionally, for Alfvénic precipitation, the modeled intensities exhibit a short lived peak at 6730 and 4278 Å, while for the latter case, the intensities are constant and dominated by 6730 and 8446 Å emissions. The modeling introduced here opens for possibilities to further advance our understanding of small scale dynamic aurora.

• Hatch, Spencer Mark; Virtanen, Ilkka; Laundal, Karl Magnus; Tesfaw, Habtamu Wubie; Vierinen, Juha & Huyghebaert, Devin Ray [Show all 8 contributors for this article] (2025). Toolkit for incoherent scatter radar experiment design and applications to EISCAT_3D. Annales Geophysicae. ISSN 0992-7689. 43(2), p. 633–649. doi: 10.5194/angeo-43-633-2025. Full text in Research Archive Show summary

  Modern phased-array incoherent scatter radar (ISR) systems consist of several thousand phased-array antenna elements. Next-generation phased-array ISR systems are shifting towards multistatic setups consisting of three sites, such as EISCAT_3D with sites in Finland, Norway, and Sweden. The tremendous flexibility that these ISR systems afford also presents a challenge: Given a science question and an estimate of the associated ionospheric conditions, how does one begin to design an ISR experiment? Here we present a method for performing observing system simulation experiments (OSSEs) with multistatic and monostatic ISRs. The method estimates the variance, or uncertainty, of measurements of three scalar quantities (plasma density, electron and ion temperature), and the covariance of one vector quantity (ion drift) in the case of multistatic systems. It is based on analytic first-order linearization of the incoherent scatter spectrum, as well as inverse and radar theory. Uncertainty estimation requires specification of the radar system as well as plasma density, electron and ion temperature, ion-neutral collision frequency, the fractional density of O+, and the mean molecular mass. We validate this analytic uncertainty estimation method against uncertainty estimates derived directly from EISCAT incoherent scatter radar measurements made over Tromsø. We also present an open-source implementation of this method and additional tools written in R and Python that may be used to assess whether a candidate experiment is likely to achieve the temporal and spatial resolution needed to study a particular phenomenon. The user may vary parameters such as integration time, bit length, and duty cycle to understand their effect on experimental uncertainties. By default the EISCAT_3D radar configuration is used and these parameters are calculated automatically via two commonly used empirical models; it is nevertheless straightforward to manually specify alternative radar configurations, whether mono- or multistatic, and individual ionospheric and atmospheric parameters. We show how different beam patterns affect reconstruction of the ionospheric potential electric field, and present an example experiment optimized for reconstructing the electrodynamics around an auroral arc.

• Brindley, N.; Madhanakumar, Mahith; Spicher, Andres; Whiter, D.; Oksavik, Kjellmar & Ogawa, Y. (2025). Intense Dynamic Optical Auroral Sub‐Structure as a Proxy for Ionospheric Density Irregularities. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 130(11). doi: 10.1029/2025ja033999. Full text in Research Archive Show summary

  When signals from Global Navigation Satellite System (GNSS) propagate through the ionosphere, disruption to the phase and amplitude of the signals can occur due to the presence of plasma density irregularities. Several phenomena have previously been associated with the formation of ionospheric irregularities, auroral precipitation being one of them; however, the nature of this relationship is still uncertain. In this study we use a suite of instruments to investigate the relationship between scintillation and an intense, discrete, dynamic auroral display on 11th January 2016. We find a temporal correlation between auroral brightness and scintillation, consistently at and around zero lag. Moreover, our analysis suggests the E‐region to be the dominant source of irregularities causing scintillation in this event. Using high‐resolution, narrow field‐of‐view observations from the Auroral Structure and Kinetics (ASK) instrument and a novel algorithm for determining scale‐dependent power in the aurora, we find evidence for a possible relationship between optical structure sizes and scintillation. The results from our analysis provide further insight into the relationship between the aurora and GNSS scintillation, and suggest a worthwhile direction for further research.

• Madhanakumar, Mahith; Spicher, Andres; Huyghebaert, Devin Ray; Kashcheyev, Anton; Spogli, Luca & Oksavik, Kjellmar [Show all 9 contributors for this article] (2025). Co‐Ordinated Observations of Multi‐Scale Irregularities Using ICEBEAR and GNSS During the May 2024 Superstorm. Space Weather. 23(8). doi: 10.1029/2025sw004411. Full text in Research Archive Show summary

  We present observations of plasma structuring from three meters up to hundreds of kilometers at auroral latitudes during the extreme geomagnetic storm of May 2024 using co‐ordinated observations from ICEBEAR and Global Navigation Satellite Systems (GNSS) receivers. Intense irregularities on all spatial scales co‐existed for about 4 hr between magnetic latitudes on 10 May during the storm's expansion phase when dense plasma structures and particle precipitation were simultaneously present at the dayside. Irregularities with scales of the order of few hundred meters remained weak thereafter following the depletion of the high latitude ionosphere even though particle precipitation was still ongoing. On the other hand, three meter E‐region irregularities and kilometer scale gradients persisted for about 24 hr, suggesting that both dayside and nightside auroral dynamics contributed to their sustained production. With the absence of an enhanced density reservoir and the region of particle precipitation shifted to higher latitudes, we observed a significant depletion in the irregularity occurrence across all scales in the dayside auroral region on 11 May.

• Buschmann, Lisa Marie; Asamura, K.; Clausen, Lasse; Jin, Yaqi; Kojima, H. & Kumamoto, A. [Show all 13 contributors for this article] (2025). Plasma structuring within an expanded polar cap and cusp studied with the SS-520-3 sounding rocket. Earth, Planets and Space. ISSN 1343-8832. 77(1). doi: 10.1186/s40623-025-02189-7. Full text in Research Archive Show summary

  The SS-520-3 sounding rocket was launched on November 4th, 2021 as part of the Grand Challenge Initiative - Cusp from Ny-Ålesund, Svalbard. The rocket was launched into the cusp ionosphere during the main phase of a geomagnetic storm. In this study we utilize two low energy particle analyzers as well as a multi-needle Langmuir probe and an impedance probe as part of the rocket payload. This study aims to provide an overview of the flight conditions from a range of ground-based instruments and scintillation receivers. We were able to confirm that the rocket entered the cusp through the poleward edge at around 74 ∘ of northern geographic latitude. Additionally, the rocket encountered polar cap patches (PCP), as well as a patch within the cusp (CP) and a newly-formed tongue of ionisation (TOI). Analysis of the density variations within different scale sizes show enhancements within meter-size and kilometer-size scales on the edges of PCP, within the CP and TOI. Overall, the enhancements within the variations on all sizes, as well as enhancements of the electron density were significantly higher within the CP and TOI in comparison to the PCP, though all structures were encountered at similar altitudes. The strongest enhancements were found on the poleward edge of the TOI, corresponding to strong fluctuations within the electron density. The TOI also had the largest enhancements within gradients of kilometer-size in comparison to meter-sizes. As the TOI is convecting with respect to the background plasma, the edges are susceptible to instabilities like the Kelvin–Helmholtz instability (KHI) and Gradient-Drift instability (GDI), giving rise to plasma density structures on several scale sizes. Graphical Abstract

• Kvammen, Andreas; Spicher, Andres; Zettergren, Matthew; Huyghebaert, Devin Ray; Rexer, Theresa & Gustavsson, Björn Johan [Show all 7 contributors for this article] (2025). Conditions for the Kelvin-Helmholtz Instability in the Polar Ionosphere. Geophysical Research Letters. ISSN 0094-8276. 52(5). doi: 10.1029/2025GL114621. Full text in Research Archive
• Madhanakumar, Mahith; Spicher, Andres; Vierinen, Juha-Pekka; Oksavik, Kjellmar; Coster, Anthea J. & Huyghebaert, Devin Ray [Show all 9 contributors for this article] (2024). The Growth and Decay of Intense GNSS Amplitude and Phase Scintillation During Non-Storm Conditions. Space Weather. 22(12). doi: 10.1029/2024SW004108. Full text in Research Archive Show summary

  A multi‐instrument study is conducted at the dayside polar ionosphere to investigate the spatio‐ temporal evolution of scintillation in Global Navigation Satellite System (GNSS) signals during non‐storm conditions. Bursts of intense amplitude and phase scintillation started to occur at ∼ 9 MLT and persisted for more than 1 hour implying the simultaneous existence of Fresnel and large‐scale sized irregularities of significant strength in the pre‐noon sector. Measurements from the EISCAT radar in Svalbard (ESR) revealed the presence of dense plasma structures with significant gradients in regions of strong Joule heating/fast flows and soft precipitation when scintillation was enhanced. Plasma structuring down to Fresnel scales were observed both in the auroral oval as well as inside the polar cap with the associated amplitude scintillation exhibiting similar strengths regardless of whether the density structures were in regions of active auroral dynamics or not. The observations are placed within the context of different sources of free energy, providing insights into the important mechanisms that generate irregularities capable of perturbing GNSS signal properties in the dayside ionosphere. Furthermore, a strong negative excursion in the interplanetary magnetic field (IMF) By component during the northward turning of Bz led to the transport of a depleted region of plasma density into the post‐noon sector that significantly weakened both amplitude and phase scintillation.

• Madhanakumar, Mahith; Spicher, Andres; Vierinen, Juha-Pekka & Oksavik, Kjellmar (2024). On the strength of E and F region irregularities for GNSS scintillation in the dayside polar ionosphere. Journal of Atmospheric and Solar-Terrestrial Physics. ISSN 1364-6826. 256. doi: 10.1016/j.jastp.2024.106197. Full text in Research Archive Show summary

  We present results of the study conducted to quantify the relative contribution of different ionospheric regions to phase scintillation in Global Navigation Satellite Systems (GNSS) at the dayside high latitude ionosphere. By taking advantage of the scanning capability of the 32-m EISCAT radar in Svalbard (ESR) and its recurrent favourable location below the dayside auroral region, we developed a methodology to identify conjunctions between the radar and GNSS satellite signals in order to compare density irregularities identified by the radar with scintillation observed in GNSS signals. The analysis revealed that the dayside ionosphere contained irregularities predominantly in the F region with scintillation occurring 77% of the times. The likelihood of observing irregularities in the E region were comparatively less with a scintillation occurrence rate of 42%. The study therefore strongly suggests that the dayside F region is more structured than the E region and is the predominant source region for irregularities that cause scintillation at GNSS frequencies. The associated ionospheric conditions revealed enhanced F region electron and ion temperatures to be collocated with scintillation for majority of the times. This supports the fact that cusp/auroral dynamics play a crucial role in creating F region irregularities which can act as sources of scintillation in GNSS signals. The presented results provide a quantitative estimate of the effectiveness of irregularities and the associated ionospheric conditions in different regions of the dayside ionosphere during scintillation, which are relevant for high latitude modelling and instability studies as well as for space weather applications.

• Kvammen, Andreas; Vierinen, Juha-Pekka; Huyghebaert, Devin Ray; Rexer, Theresa; Spicher, Andres & Gustavsson, Björn Johan [Show all 7 contributors for this article] (2024). NOIRE-Net–a convolutional neural network for automatic classification and scaling of high-latitude ionograms. Frontiers in Astronomy and Space Sciences. 11. doi: 10.3389/fspas.2024.1289840. Full text in Research Archive Show summary

  Millions of ionograms are acquired annually to monitor the ionosphere. The accumulated data contain untapped information from a range of locations, multiple solar cycles, and various geomagnetic conditions. In this study, we propose the application of deep convolutional neural networks to automatically classify and scale high-latitude ionograms. A supervised approach is implemented and the networks are trained and tested using manually analyzed oblique ionograms acquired at a receiver station located in Skibotn, Norway. The classification routine categorizes the observations based on the presence or absence of E− and F-region traces, while the scaling procedure automatically defines the E− and F-region virtual distances and maximum plasma frequencies. Overall, we conclude that deep convolutional neural networks are suitable for automatic processing of ionograms, even under auroral conditions. The networks achieve an average classification accuracy of 93% ± 4% for the E-region and 86% ± 7% for the F-region. In addition, the networks obtain scientifically useful scaling parameters with median absolute deviation values of 118 kHz ±27 kHz for the E-region maximum frequency and 105 kHz ±37 kHz for the F-region maximum O-mode frequency. Predictions of the virtual distance for the E− and F-region yield median distance deviation values of 6.1 km ± 1.7 km and 8.3 km ± 2.3 km, respectively. The developed networks may facilitate EISCAT 3D and other instruments in Fennoscandia by automatic cataloging and scaling of salient ionospheric features. This data can be used to study both long-term ionospheric trends and more transient ionospheric features, such as traveling ionospheric disturbances.

• Buschmann, Lisa Marie; Clausen, Lasse; Spicher, Andres; Ivarsen, Magnus Fagernes & Miloch, Wojciech Jacek (2024). Statistical Studies of Plasma Structuring in the Auroral Ionosphere by the Swarm Satellites. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 129(2). doi: 10.1029/2023JA032097. Full text in Research Archive Show summary

  This study uses over 2 years of 16 Hz density measurements, 50 Hz magnetic field data and ROTI data from the Swarm mission to perform long term statistics of plasma structuring in the polar ionosphere. The timeframe covers more than 2 years near the 24th solar cycle peak. We additionally use 3 years of data obtained from a timeframe close to solar minimum for discussion. We present power spectral densities (PSD) of electron density irregularities and magnetic field for 1‐min intervals. These PSD have been characterized by the probability of a slope steepening, and by integrating the power deposited within frequency intervals corresponding to kilometer scales. For the electron density, we observe seasonal dependencies for both the integrated power and slope characteristics. While the dual slope probability, especially within the polar cap, varies with solar EUV‐radiation, the integrated power is strongest around the equinoxes. Additionally, while we found similar results for the slope probability for both hemispheres, the integrated power exhibits strong hemispheric asymmetries with stronger enhancements within local summer in the southern hemisphere. The ROTI data shows a similar seasonal variability as the density PSD integrated power, in both seasonal dependency and interhemispheric variability. However, for the ROTI data the strongest fluctuations were found within the nightside auroral oval and the cusp. For the PSD of the magnetic field data, we obtain the strongest enhancements within the cusp for all seasons and all hemispheres. The fluctuations may indicate an increase in Alfvénic energy associated with a downward Poynting flux.

• Cameron, T.G.; Fiori, R.A.D.; Perry, G.W.; Spicher, Andres & Thayaparan, T. (2024). Statistical Analysis of Off-Great Circle Radio Wave Propagation in the Polar Cap. Radio Science. ISSN 0048-6604. 59(4). doi: 10.1029/2023RS007897. Full text in Research Archive Show summary

  High latitude ionospheric density structures such as polar cap patches and arcs are capable of deflecting high frequency (HF) radio waves to off‐great circle paths, and are likely detrimental to technologies dependent on HF radio propagation. In this study, nearly 2.5 years of 4.6–14.4 MHz data from a multi‐frequency HF radio link between Qaanaaq, Greenland and Alert, Canada are used to investigate high‐latitude off‐great circle propagation in the polar cap. After an example of HF radio propagation affected by polar cap patches is shown in detail, a statistical analysis of the occurrence and impacts of off‐great circle deflections in the polar cap is presented. Off‐great circle propagation is shown to be increasingly common with increasing frequency up to 11.1 MHz, such that averaged over 1 year, received 11.1 MHz signals experienced deflections >30° from the great circle direction 65.6% of the time. The occurrence of these deflections across the year is shown to be at a maximum in the winter, while occurrence across the day varies with season. Trends across both time of day and time of year for 11.1 and 14.4 MHz deflections are consistent with polar cap patch occurrence trends. Off‐great circle deflections are shown to be associated with increased time‐of‐flights, a larger range of positive and negative Doppler shifts, increased Doppler spreads, and lower signal‐to‐noise ratios. These results are discussed in the context of ionospheric phenomena in the polar cap, and implications for over‐the‐horizon radars operating at high latitudes.

• Frøystein, Ingeborg; Spicher, Andres; Gustavsson, Björn Johan; Oksavik, Kjellmar & Johnsen, Magnar Gullikstad (2024). On the Identification of the Dayside Auroral Region Using Incoherent Scatter Radar. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 129(12). doi: 10.1029/2024JA033361. Full text in Research Archive Show summary

  This paper presents a robust method combining electron temperatures and density to identify the winter dayside auroral region in Incoherent Scatter Radar (ISR) observations. In literature, a common proxy for identifying the dayside auroral region has been enhanced electron temperatures T e at high altitudes. However, T e is intimately related to N e and their relationship is not completely settled. In this study, the relation between T e , N e , and the precipitation heat source Q is quantified. Using ESR fast elevation scans in the winter dayside auroral region, the intimate relationship between these three parameters is investigated. T e decreases roughly linearly with exponentially increasing N e , irrespective of the heat source. Precipitation creates a heated population with T e above roughly 2,000 K (i.e., 500–1,300 K higher than the background plasma). Several extensions to the purely T e based method were examined, and it is found that combining T e and N e yields consistent boundaries when compared to magnetic disturbance data from Swarm satellites and 6,300 Å auroral observations. Future applications of characterizing ionospheric dynamics are discussed.

• Jin, Yaqi; Moen, Jøran Idar; Spicher, Andres; Liu, Jianjun; Clausen, Lasse & Miloch, Wojciech Jacek (2023). Ionospheric Flow Vortex Induced by the Sudden Decrease in the Solar Wind Dynamic Pressure. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 128(11). doi: 10.1029/2023JA031690. Full text in Research Archive Show summary

  Abrupt changes in the solar wind dynamic pressure can greatly affect the Earth's magnetosphere-ionosphere system. We present an ionospheric flow vortex in the morning sector during the sudden decrease in the solar wind dynamic pressure. The flow vortex was clearly observed by both the Hankasalmi radar and the azimuthal scan mode of the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR). The flow vortex was first seen in the eastern field of view (FOV) of the Hankasalmi radar, and then propagated poleward and westward into the FOV of the ESR. During the passage of the flow vortex, a gradual decrease of electron density was observed by the field-aligned ESR 42 m antenna. When the equatorward directed ionospheric flow reached the ESR site, weak and visible increases in the electron density and electron temperature were observed. This impact was likely caused by soft electron precipitation associated with the clockwise flow vortex and upward field-aligned current. The azimuthal scan mode of the ESR 32 m radar at low elevation angle (30°) allowed us to measure key ionospheric parameters over a larger area (6° in latitude and 120° in azimuthal angle). The latitudinal scan of the electron temperature was used to proxy the equatorward auroral boundary, which shows that the flow vortex was located in the subauroral region. We further demonstrated that it is possible to study the weak increase of electron density by using GPS total electron content (TEC) data. A minor TEC increase was observed near the center of the flow vortex.

• Stamm, Johann Immanuel; Vierinen, Juha; Gustavsson, Bjorn Johan & Spicher, Andres (2023). A technique for volumetric incoherent scatter radar analysis. Annales Geophysicae. ISSN 0992-7689. 41(1), p. 55–67. doi: 10.5194/angeo-41-55-2023. Full text in Research Archive Show summary

  Volumetric measurements of the ionosphere are important for investigating spatial variations of ionospheric features, like auroral arcs and energy deposition in the ionosphere. In addition, such measurements make it possible to distinguish between variations in space and time. While spatial variations in scalar quantities such as electron density or temperature have been investigated with incoherent scatter radar (ISR) before, spatial variation in the ion velocity, which is a vector quantity, has been hard to measure. The upcoming EISCAT3D radar will be able to do volumetric measurements of ion velocity regularly for the first time. In this paper, we present a technique for relating volumetric measurements of ion velocity to neutral wind and electric field. To regularize the estimates, we use Maxwell's equations and fluid-dynamic constraints. The study shows that accurate volumetric estimates of electric field can be achieved. Electric fields can be resolved at altitudes above 120 km, which is the altitude range where auroral current closure occurs. Neutral wind can be resolved at altitudes below 120 km.

• Baddeley, Lisa; Lorentzen, Dag Arne; Haaland, Stein Egil; Heino, Erkka Petteri; Mann, Ingrid Brigitte & Miloch, Wojciech Jacek [Show all 10 contributors for this article] (2023). Space and atmospheric physics on Svalbard: a case for continued incoherent scatter radar measurements under the cusp and in the polar cap boundary region. Progress in Earth and Planetary Science. 10. doi: 10.1186/s40645-023-00585-9. Full text in Research Archive Show summary

  Incoherent scatter radars (ISRs) represent the only instrument (both ground and space based) capable of making high temporal and spatial resolution measurements of multiple atmospheric parameters—such as densities, temperatures, particle velocities, mass flux—over an altitude range covering the entire mesosphere/lower thermosphere/ionosphere (MLTI) system on a quasi-continuous basis. The EISCAT Svalbard incoherent scatter radar (ESR), located just outside Longyearbyen (78.15∘ N) on Svalbard, is the only currently operating facility capable of making such measurements inside the polar cusp—an area of significant energy input into the atmosphere and characterized by heating instabilities and turbulence. The ESR was built in the mid-1990s and has provided valuable data for the international experimental and modelling communities. New radar technologies are now available, in the form of phased array systems, which offer new data products and operational flexibility. This paper outlines the achievements and current research focus of the ESR and provides scientific arguments, compiled from inputs across the international scientific community, for a new phased array ISR facility on Svalbard. In addition to the fundamental scientific arguments, the paper discusses additional benefits of continued ISR observations on Svalbard, building on the key findings of the ESR. Svalbard has a large network of complementary instrumentation both focused on the MLTI system (e.g. the Kjell Henriksen auroral Observatory, the Svalbard SuperDARN radar and the Svalrak sounding rocket launch facility) with synergies to other research fields, such as meteorology and oceanography. As a further holistic system science view of the Earth becomes more important, a new ISR on Svalbard will be important also in this respect with its ability to provide datasets with a wide range of scientific applications. Increased activity in space has highlighted problematic issues such as space debris. A changing Arctic has also seen increased human activity via the opening up of new shipping routes, which are reliant on GNSS technology that is effected by severe turbulence in the MLTI system. As such, societal applications of a future ISR are also presented. The accessibility and logistical support for such a facility is also briefly discussed.

• Buschmann, Lisa Marie; Bonnell, John W.; Bounds, Scott; Clausen, Lasse; Kletzing, Craig & Marholm, Sigvald [Show all 9 contributors for this article] (2023). The role of particle precipitation on plasma structuring at different altitudes by in-situ measurements. Journal of Space Weather and Space Climate. 13. doi: 10.1051/swsc/2023012. Full text in Research Archive Show summary

  The plasma in the cusp ionosphere is subject to particle precipitation, which is important for the development of large-scale irregularities in the plasma density. These irregularities can be broken down into smaller scales which have been linked to strong scintillations in the Global Navigation Satellite System (GNSS) signals. We present power spectra for the plasma density irregularities in the cusp ionosphere for regions with and without auroral particle precipitation based on in-situ measurements from the Twin Rockets to Investigate Cusp Electrodynamics-2 (TRICE-2) mission, consisting of two sounding rockets flying simultaneously at different altitudes. The electron density measurements taken from the multi-needle Langmuir probe system (m-NLP) were analyzed for the whole flight duration for both rockets. Due to their high sampling rates, the probes allow for a study of plasma irregularities down to kinetic scales. A steepening of the slope in the power spectra may indicate two regimes, a frequency interval with a shallow slope, where fluid-like processes are dominating, and an interval with a steeper slope which can be addressed with kinetic theory. The steepening occurs at frequencies between 20 Hz and 100 Hz with a median similar to the oxygen gyrofrequency. Additionally, the occurrence of double slopes increases where precipitation starts and throughout the rest of the flight. In addition, strong electron density fluctuations were found in regions poleward of the cusp, thus in regions immediately after precipitation. Furthermore, by investigating the integrated power of the fluctuations within different frequency ranges, we show that at low frequencies (10–100 Hz), the power is pronounced more evenly while the rocket encounters particle precipitation, while at high frequencies (100–1000 Hz) fluctuations essentially coincide with the passing through a flow channel.

• Zhang, Shun-Rong; Nishimura, Yukitoshi; Vierinen, Juha-Pekka; Lyons, Larry R.; Knipp, Delores J. & Gustavsson, Björn Johan [Show all 11 contributors for this article] (2023). Simultaneous Global Ionospheric Disturbances Associated With Penetration Electric Fields During Intense and Minor Solar and Geomagnetic Disturbances. Geophysical Research Letters. ISSN 0094-8276. 50(19). doi: 10.1029/2023GL104250. Full text in Research Archive Show summary

  A new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance (SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace disturbances: a Coronal Mass Ejection-driven severe disturbance event, a high-speed stream event, and a minor disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with a ∼1% TEC increase. Notably, SGDs can occur under minor solar-geomagnetic disturbances. SGDs are likely caused by penetration electric fields (PEFs) of solar-geomagnetic origin, as they are associated with Bz southward, increased auroral AL/AU, and solar wind pressure enhancements. These findings offer new insights into the nature of PEFs and their ionospheric impact while confirming some key earlier results obtained through alternative methods. Importantly, the accessibility of extensive GNSS networks, with at least 6,000 globally distributed receivers for ionospheric research, means that rich PEF information can be acquired, offering researchers numerous opportunities to investigate geospace electrodynamics.

• Ivarsen, Magnus Fagernes; Jin, Yaqi; Spicher, Andres; St-Maurice, Jean-Pierre; Park, Jaeheung & Billett, Daniel (2023). GNSS Scintillations in the Cusp, and the Role of Precipitating Particle Energy Fluxes. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 128(10). doi: 10.1029/2023JA031849. Full text in Research Archive Show summary

  Using a large data set of ground-based GNSS scintillation observations coupled with in situ particle detector data, we perform a statistical analysis of both the input energy flux from precipitating particles, and the observed occurrence of density irregularities in the northern hemisphere cusp. By examining trends in the two data sets relating to geomagnetic activity, we conclude that observations of irregularities in the cusp grows increasingly likely during storm-time, whereas the precipitating particle energy flux does not. We thus find a weak or nonexistent statistical link between geomagnetic activity and precipitating particle energy flux in the cusp. This is a result of a previously documented tendency for the cusp energy flux to maximize during northward IMF, when density irregularities tend not to be widespread, as we demonstrate. At any rate, even though ionization and subsequent density gradients directly caused by soft electron precipitation in the cusp are not to be ignored for the trigger of irregularities, our results point to the need to scrutinize additional physical processes for the creation of irregularities causing scintillations in and around the cusp. While numerous phenomena known to cause density irregularities have been identified and described, there is a need for a systematic evaluation of the conditions under which the various destabilizing mechanisms become important and how they sculpt the observed ionospheric “irregularity landscape.” As such, we call for a quantitative assessment of the role of particle precipitation in the cusp, given that other factors contribute to the production of irregularities in a major way.

• Huyghebaert, Devin Ray; Chau, Jorge L.; Spicher, Andres; Ivarsen, Magnus Fagernes; Clahsen, Matthias & Latteck, Ralph [Show all 7 contributors for this article] (2023). Investigating Spatial and Temporal Structuring of E-Region Coherent Scattering Regions Over Northern Norway. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 128(10). doi: 10.1029/2023JA031682. Full text in Research Archive Show summary

  Recently, it has been shown that the Spread Spectrum Interferometric Multistatic meteor radar Observing Network radar system located in northern Norway is capable of measuring ionospheric E-region coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s, respectively. Four different events from June and July of 2022 are examined in the present study, where the coherent scatter measurements are used as a tracer for large-scale ionospheric phenomena such as plasma density enhancements and ionospheric electric fields. By applying a two-dimensional Fourier analysis to range-time-intensity data, we perform a multi-scale spatial and temporal investigation to determine the change in range over time of large-scale ionospheric structures (>3 km) which are compared with line-of-sight velocities of the small scale structures (∼5 m) determined from the Doppler shift of the coherent scatter. The spectral characteristics of the large-scale structures are also investigated and logarithmic spectral slopes for scale sizes of 100–10 km were found to be between −3.0 and −1.5. This agrees with much of the previous work on the spatial spectra scaling for ionospheric electric fields. This analysis aids in characterizing the source of the plasma turbulence and provides crucial information about how energy is redistributed from large to small scales in the E-region ionosphere.

• Ivarsen, Magnus Fagernes; Lozinsky, Adam; St-Maurice, Jean-Pierre; Spicher, Andres; Huyghebaert, Devin Ray & Hussey, Glenn C. [Show all 9 contributors for this article] (2023). The Distribution of Small-Scale Irregularities in the E-Region, and Its Tendency to Match the Spectrum of Field-Aligned Current Structures in the F-Region. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 128(5). doi: 10.1029/2022JA031233. Full text in Research Archive Show summary

  We associate new data from icebear, a coherent scatter radar located in Saskatchewan, Canada, with scale-dependent physics in the ionosphere. We subject the large-scale icebear 3D echo patterns (treated as 2D point clouds) to a data analysis technique hitherto never applied to the ionosphere, a technique that is widely applied in cosmological red-shift surveys to characterize the spatial clustering of galaxies. The technique results in a novel method to calculate the spatial power spectral density of the greater ionospheric irregularity field. We compare results from this method to in-situ plasma density and magnetic field observations from the Swarm mission. We show that there is a remarkable similarity between echo clustering spectra in the E-region and the field-aligned current structuring spectrum observed in the F-region: a clear and characteristic preferred scale (5 km) both in the E- and F-region spectra. We discuss the possibility that this represents evidence of an energy injection into the ionospheric irregularity field via energetic particle precipitation, but offer alternative interpretations with wider connotations for the ionosphere-magnetosphere system. These findings open new and promising avenues of research for the study of the location of ionospheric scatter echoes with 3D information. It constitutes a novel way to consider the pattern of ionospheric irregularities over wide fields of view when there is an abundance of radar echoes, which allows for the analysis of radar data as point clouds.

• Ivarsen, Magnus Fagernes; St‐Maurice, Jean-Pierre; Hussey, Glenn C.; Spicher, Andres; Jin, Yaqi & Lozinsky, Adam [Show all 10 contributors for this article] (2023). Measuring small-scale plasma irregularities in the high-latitude E- and F-regions simultaneously. Scientific Reports. 13. doi: 10.1038/s41598-023-38777-4. Full text in Research Archive Show summary

  The ionosphere, Earth’s space environment, exhibits widespread turbulent structuring, or plasma irregularities, visualized by the auroral displays seen in Earth’s polar regions. Such plasma irregularities have been studied for decades, but plasma turbulence remains an elusive phenomenon. We combine scale-dependent measurements from a ground-based radar with satellite observations to characterize small-scale irregularities simultaneously in the bottomside and topside ionosphere and perform a statistical analysis on an aggregate from both instruments over time. We demonstrate the clear mapping of information vertically along the ionospheric altitude column, for field-perpendicular wavelengths down to 1.5 km. Our results paint a picture of the northern hemisphere high-latitude ionosphere as a turbulent system that is in a constant state of growth and decay; energy is being constantly injected and dissipated as the system is continuously attempting an accelerated return to equilibrium. We connect the widespread irregularity dissipation to Pedersen conductance in the E-region, and discuss the similarities between irregularities found in the polar cap and in the auroral region in that context. We find that the effects of a conducting E-region on certain turbulent properties (small-scale spectral index) is near ubiquitous in the dataset, and so we suggest that the electrodynamics of a conducting E-region must be considered when discussing plasma turbulence at high latitudes. This intimate relationship opens up the possibility that E-region conductivity is associated with the generation of F-region irregularities, though further studies are needed to assess that possibility.

• Spicher, Andres; LaBelle, James; Bonnell, John W.; Roglans, Roger; Moser, Chrystal & Fuselier, Stephen A. [Show all 18 contributors for this article] (2022). Interferometric Study of Ionospheric Plasma Irregularities in Regions of Phase Scintillations and HF Backscatter. Geophysical Research Letters. ISSN 0094-8276. 49(12). doi: 10.1029/2021GL097013. Full text in Research Archive Show summary

  We investigate the nature of small-scale irregularities observed in the cusp by the Twin Rockets to Investigate Cusp Electrodynamics-2 (TRICE-2) in regions of enhanced phase scintillations and high-frequency coherent radar backscatter. We take advantage of the fact that the irregularities were detected by spatially separated probes, and present an interferometric analysis of both the observed electron density and electric field fluctuations. We provide evidence that fluctuations spanning a few decameters to about a meter have low phase velocity in the plasma reference frame and are nondispersive, confirming that decameter-scale irregularities follow the E × B velocity. Furthermore, we show that these “spatial” structures are intermittent and prominent outside of regions with strongest precipitation. The observations are then discussed in the context of possible mechanisms for irregularity creation.

• Zhang, Shun-Rong; Vierinen, Juha; Aa, Ercha; Goncharenko, Larisa P.; Erickson, Philip J. & Rideout, William [Show all 8 contributors for this article] (2022). 2022 Tonga Volcanic Eruption Induced Global Propagation of Ionospheric Disturbances via Lamb Waves. Frontiers in Astronomy and Space Sciences. 9. doi: 10.3389/fspas.2022.871275. Full text in Research Archive Show summary

  The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. This study provides a global picture of ionospheric disturbances over an extended period for at least 4 days. We find traveling ionospheric disturbances (TIDs) radially outbound and inbound along entire Great-Circle loci at primary speeds of ∼300–350 m/s (depending on the propagation direction) and 500–1,000 km horizontal wavelength for front shocks, going around the globe for three times, passing six times over the continental US in 100 h since the eruption. TIDs following the shock fronts developed for ∼8 h with 10–30 min predominant periods in near- and far- fields. TID global propagation is consistent with the effect of Lamb waves which travel at the speed of sound. Although these oscillations are often confined to the troposphere, Lamb wave energy is known to leak into the thermosphere through channels such as atmospheric resonance at acoustic and gravity wave frequencies, carrying substantial wave amplitudes at high altitudes. Prevailing Lamb waves have been reported in the literature as atmospheric responses to the gigantic Krakatoa eruption in 1883 and other geohazards. This study provides substantial first evidence of their long-duration imprints up in the global ionosphere. This study was enabled by ionospheric measurements from 5,000+ world-wide Global Navigation Satellite System (GNSS) ground receivers, demonstrating the broad implication of the ionosphere measurement as a sensitive detector for atmospheric waves and geophysical disturbances.

• Takahashi, Toru; Spicher, Andres; Mare, Francesca Di; Rowland, Douglas E.; Pfaff, Robert F. & Collier, Michael R. [Show all 8 contributors for this article] (2022). Suppression of ionospheric irregularity due to auroral particle impact. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 127(1). doi: 10.1029/2020JA028725. Full text in Research Archive Show summary

  The VISIONS-2 35.039 sounding rocket was launched from Ny-Ålesund, Svalbard, on 7 December 2018 at 11:06 UT, and traveled overhead of the cusp aurora. The payload reached an apogee of 806.6 km and provided measurements of the electric field (E) and electron density (N_e ) with a high sampling rate of 6,250 Hz. The high-sampling-data make it possible to estimate the horizontal structure of E and Ne on scales ranging from meters to kilometers scale. The horizontal variation in the electron density and electric field (ΔN_e /N_e and ΔE) and integrated power of N_e and E (ΣP_Ne and ΣP_E) for 1–10, 10–100, and 100–1,000 Hz range were derived. The derived values were compared with the 557.7 and 630.0 nm emission intensities obtained from an all-sky camera installed in Ny-Ålesund projected at the footprint of the rocket, which was calculated by tracing the Earth's magnetic field line from the rocket altitude to the emission layer. ΔN_e /N_e , ΔE, ΣP_Ne, and ΣP_E increased with the 630.0 nm emission intensity. Of particular interest is the lower level irregularity was observed when the 557.7 nm emission intensity exceeded 4.5 kR compared with other time interval. This may suggest that particle impact ionization created sufficient Pedersen conductance in the E-region to short the F-region current. This short-circuit seemed to cause the suppression of the irregularities in the F-region and lower level irregularities were also observed in the rocket altitude.

• Mann, Ingrid Brigitte; Olsen, Sveinung viggo; Eilertsen, Yngve; Pineau, Adrien; Palinkas, Sabina Strmic & Gunnarsdóttir, Tinna Líf [Show all 9 contributors for this article] (2022). MESOSPHERIC DUST STUDIES WITH MXD2. ESA SP. ISSN 0379-6566. SP-743, p. 255–258. Full text in Research Archive
• Aa, Ercha; Zhang, Shunrong; Erickson, Philip J.; Vierinen, Juha; Coster, Anthea J. & Goncharenko, Larisa P. [Show all 8 contributors for this article] (2022). Significant Ionospheric Hole and Equatorial Plasma Bubbles After the 2022 Tonga Volcano Eruption. Space Weather. 20(7). doi: 10.1029/2022SW003101. Full text in Research Archive Show summary

  This paper investigates the local and global ionospheric responses to the 2022 Tonga volcano eruption, using ground-based Global Navigation Satellite System total electron content (TEC), Swarm in situ plasma density measurements, the Ionospheric Connection Explorer (ICON) Ion Velocity Meter (IVM) data, and ionosonde measurements. The main results are as follows: (a) A significant local ionospheric hole of more than 10 TECU depletion was observed near the epicenter ∼45 min after the eruption, comprising of several cascading TEC decreases and quasi-periodic oscillations. Such a deep local plasma hole was also observed by space-borne in situ measurements, with an estimated horizontal radius of 10–15° and persisted for more than 10 hr in ICON-IVM ion density profiles until local sunrise. (b) Pronounced post-volcanic evening equatorial plasma bubbles (EPBs) were continuously observed across the wide Asia-Oceania area after the arrival of volcano-induced waves; these caused a N_e decrease of 2–3 orders of magnitude at Swarm/ICON altitude between 450 and 575 km, covered wide longitudinal ranges of more than 140°, and lasted around 12 hr. (c) Various acoustic-gravity wave modes due to volcano eruption were observed by accurate Beidou geostationary orbit (GEO) TEC, and the huge ionospheric hole was mainly caused by intense shock-acoustic impulses. TEC rate of change index revealed globally propagating ionospheric disturbances at a prevailing Lamb-wave mode of ∼315 m/s; the large-scale EPBs could be seeded by acoustic-gravity resonance and coupling to less-damped Lamb waves, under a favorable condition of volcano-induced enhancement of dusktime plasma upward E×B drift and postsunset rise of the equatorial ionospheric F-layer.

• Aa, Ercha; Zhang, Shun-Rong; Wang, Wenbing; Erickson, Philip J.; Qian, Liying & Eastes, Richard W. [Show all 15 contributors for this article] (2022). Pronounced Suppression and X-Pattern Merging of Equatorial Ionization Anomalies After the 2022 Tonga Volcano Eruption. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 127(6). doi: 10.1029/2022JA030527. Full text in Research Archive Show summary

  Following the 2022 Tonga Volcano eruption, dramatic suppression and deformation of the equatorial ionization anomaly (EIA) crests occurred in the American sector ∼14,000 km away from the epicenter. The EIA crests variations and associated ionosphere-thermosphere disturbances were investigated using Global Navigation Satellite System total electron content data, Global-scale Observations of the Limb and Disk ultraviolet images, Ionospheric Connection Explorer wind data, and ionosonde observations. The main results are as follows: (a) Following the eastward passage of expected eruption-induced atmospheric disturbances, daytime EIA crests, especially the southern one, showed severe suppression of more than 10 TEC Unit and collapsed equatorward over 10° latitudes, forming a single band of enhanced density near the geomagnetic equator around 14–17 UT, (b) Evening EIA crests experienced a drastic deformation around 22 UT, forming a unique X-pattern in a limited longitudinal area between 20 and 40°W. (c) Thermospheric horizontal winds, especially the zonal winds, showed long-lasting quasi-periodic fluctuations between ±200 m/s for 7–8 hr after the passage of volcano-induced Lamb waves. The EIA suppression and X-pattern merging was consistent with a westward equatorial zonal dynamo electric field induced by the strong zonal wind oscillation with a westward reversal.

• Brask, Steffen Mattias; Marholm, Sigvald; Mare, Francesca Di; Adhikari, Sayan; Spicher, Andres & Takahashi, T. [Show all 7 contributors for this article] (2022). Electron-neutral collisions effects on Langmuir probe in the lower E-region ionosphere. Physics of Plasmas. ISSN 1070-664X. 29(3). doi: 10.1063/5.0079761. Full text in Research Archive Show summary

  We present the first set of particle-in-cell simulations including Monte Carlo collisions between charged and neutral particles used to simulate a cylindrical Langmuir probe in the electron saturation regime with a collisional electron sheath. We use a setup focused on the E-region ionosphere; however, the results of these simulations are analyzed in a general sense using dimensionless values. We find that the electron currents get enhanced as the collision frequency for electrons increases and the values of <i>𝜆��𝑒��/𝜆��𝐷��→1</i>, where <i>λe</i> is the electron mean free path and <i>λD</i> is the electron Debye length. In addition, we apply the simulation results to a sounding rocket experiment and show how we can correct the currents for the Investigation of Cusp Irregularities-4 sounding rocket due to collisions while it flies through the E-region.

• Mann, Ingrid; Olsen, Sveinung Viggo; Eilertsen, Yngve; Trollvik, Henriette Marie Tveitnes; Pinneau, Adrien & Palinkas, Sabina Strmic [Show all 11 contributors for this article] (2022). Mesospheric Dust Studies with MXD2. ESA SP. ISSN 0379-6566. Full text in Research Archive
• Olifer, L.; Feltman, C.; Ghaffari, R.; Henderson, S.; Huyghebaert, Devin & Burchill, J. [Show all 12 contributors for this article] (2021). Swarm Observations of Dawn/Dusk Asymmetries Between Pedersen Conductance in Upward and Downward Field-Aligned Current Regions. Earth and Space Science. 8(7). doi: 10.1029/2020EA001167. Full text in Research Archive Show summary

  The locations of region 1 and 2 field-aligned current systems were determined using fluxgate magnetometer measurements from 875 dawn-dusk passes of the Swarm A satellite. Within each field-aligned current region, the ionospheric Pedersen conductance was derived from the newly corrected Swarm electric and magnetic field measurements. The Pedersen conductances are generally consistent with photoionization models. However, we show that the in situ method of determining Pedersen conductance allows for a more complete description of magnetosphere-ionosphere coupling and should be used in future studies when possible. We show that, overall, the Pedersen conductance is larger in the upward current region than in the downward region by ∼0.6 S on the dawn side of the Earth. Meanwhile, the dusk side Pedersen conductance is equivalent in both current regions. We attribute this asymmetry to dawn side energetic electron precipitation, commonly associated with substorm electron injections from the magnetotail.

• Ivarsen, Magnus Fagernes; St-Maurice, Jean-Pierre; Jin, Yaqi; Park, Jaeheung; Miloch, Wojciech Jacek & Spicher, Andres [Show all 8 contributors for this article] (2021). Steepening Plasma Density Spectra in the Ionosphere: The Crucial Role Played by a Strong E-Region. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 126(8). doi: 10.1029/2021JA029401. Full text in Research Archive Show summary

  Based on the Swarm 16 Hz Advanced Plasma Density data set, and using the Swarm A satellite, we apply automatic detection of spectral breaks in seven million sampled plasma density power spectra in the high-latitude F-region ionosphere. This way, we survey the presence of plasma irregularity dissipation due to an enhanced E-region conductance, caused both by solar photoionization and particle precipitation. We introduce a new quantity named the steepening slope index (SSI) which we use to estimate the occurrence rate of break-points in sampled plasma densities. We provide an interpretation of SSI in the context of solar photoionization-induced conductance enhancements of the E-region. We present a comprehensive climatology of the SSI occurrence rate, along with statistics documenting characteristic high-latitude plasma density spectra. In the absence of steepening, the typical spectral index is 2.1. When density spectra steepen, the index is typically 1.6 at large scales, and 2.7 at small scales. We discuss the impact of high-energy deeply penetrating electron precipitation in the diffuse aurora, and precipitating electrons in the aurora at large. Here, a key finding is that near the cusp, where the F-region conductance is enhanced, spectra tend not to steepen. We find that both the diffuse and discrete aurora are modulating F-region plasma irregularity dissipation through an enhancement of E-region conductance, highlighting the role played by factors other than solar zenith angle in high-latitude plasma dynamics. The influence of E-region conductance on spectral shapes indicates the need for a new discussion of how particle precipitation can structure the local winter high-latitude F-region ionosphere.

• Moser, Chrystal; LaBelle, James William; Hatch, Spencer Mark; Moen, Jøran Idar; Spicher, Andres & Takahashi, Toru [Show all 11 contributors for this article] (2021). The Cusp as a VLF Saucer Source: First Rocket Observations of Long‐Duration VLF Saucers on the Dayside. Geophysical Research Letters. ISSN 0094-8276. 48(2). doi: 10.1029/2020GL090747. Full text in Research Archive Show summary

  Auroral whistler‐mode radio emissions called saucers are of fundamental interest because they require an unusually stationary emission process in the dynamic auroral environment, and it is a mystery how that can happen in this or similar conditions elsewhere in geospace. The Cusp Alfvén and Plasma Electrodynamics Rocket (CAPER‐2), launched into the cusp, obtained the first rocket measurements of a large‐scale, multiple‐armed dayside saucer, similar to those observed by the DEMETER satellite, with the addition of particle measurements and ground‐based measurements. Analysis of saucer shapes, directional measurements using waveforms, and ground‐based data show that, accounting for estimated uncertainties, these originate at altitudes ∼4,000 km within the cusp, the eastern side of which is penetrated by the rocket ∼100 s after the saucers are encountered. On‐board particle instruments show dispersed electron bursts in the cusp, Alfvénically accelerated at altitudes at or above the saucer sources.

• Mare, Francesca Di; Spicher, Andres; Clausen, Lasse; Miloch, Wojciech Jacek & Moen, Jøran Idar (2021). Turbulence and Intermittency in the Winter Cusp Ionosphere Studied With the ICI Sounding Rockets. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 126(8). doi: 10.1029/2021JA029150. Full text in Research Archive Show summary

  The characteristics of turbulent plasma in the winter cusp ionosphere is studied based on in-situ data from the Investigation of Cusp Irregularities (ICI) sounding rockets. The electron density fluctuations from ICI-2 and ICI-3 missions have been analyzed for the whole flight, using advanced timeseries analysis techniques. The analysis of the autocorrelation scale is indicative of the turbulence integral scale and marks the onset of the turbulent cascade from large to small scales in the power spectrum density of the rocket data. The power spectrum is typical for a turbulent field. The turbulent structures are persistent in the data, which are quantified by analyzing the Probability Distribution Functions (PDFs) and their deviations from the Gaussian distribution. The kurtosis analysis indicates the presence of intermittency. These results are compared with the Local Intermittence Measure - LIM, which confirms the presence of small scale intermittent structures. The turbulence measured by rockets appears well developed and covers frequencies between 1 Hz and several hundred Hz. There is a good agreement with the previous results, suggesting that density fluctuations in the ionospheric cusp agree with the turbulence framework in which intermittent processes transfer energy across different scales.

• Ivarsen, Magnus Fagernes; Jin, Yaqi; Spicher, Andres; Miloch, Wojciech Jacek & Clausen, Lasse (2021). The Lifetimes of Plasma Structures at High Latitudes. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 126. doi: 10.1029/2020JA028117. Full text in Research Archive Show summary

  We present an investigation of polar cap plasma structure lifetimes. We analyze both simulated data from ionospheric models (International Reference Ionosphere model and Mass Spectrometer Incoherent Scatter model) and in situ data from the Swarm satellite mission (the 16 Hz Advanced Plasma Density dataset). We find that the theoretical prediction that E-region conductance is a predictor of F-region polar cap plasma structure lifetimes is indeed supported by both in situ-based observations and by ionospheric models. In situ plasma structure lifetimes correlate well with the ratio of F- to E-region conductance. We present explicit predictions of small scale (∼1 km) structure lifetimes, which range from less than 1 h during local summer to around 3 h during local winter. We highlight a large discrepancy between the observational and theoretical scale-dependency of decay due to diffusion.

• Jin, Yaqi; Clausen, Lasse; Spicher, Andres; Ivarsen, Magnus Fagernes; Zhang, Yongliang & Miloch, Wojciech Jacek [Show all 7 contributors for this article] (2021). Statistical Distribution of Decameter Scale (50 m) Ionospheric Irregularities at High Latitudes. Geophysical Research Letters. ISSN 0094-8276. 48(19). doi: 10.1029/2021GL094794. Full text in Research Archive Show summary

  We present a study of decameter scale ionospheric irregularities using in-situ electron density data from the NorSat-1 satellite. During the current period of low solar activity, NorSat-1 frequently observes significant plasma irregularities from several 10 s km down to several decameter. These are often observed near the dayside cusp and dawnside auroral zone. The decameter-scale irregularities are positively correlated with intermediate-scale (10 km) density gradients, for both negative and positive gradients encountered by the satellite. The statistical distribution of electron density over two winter months in the northern hemisphere along NorSat-1 orbits, shows significant density increases in the cusp ionosphere (75°–80° Magnetic LATitude) and in regions near the dawnside auroral oval. Intermediate scale density gradients and small-scale irregularities are clearly associated with these density enhancements. We postulate that these density enhancements and irregularities are due to auroral particle precipitation/plasma dynamics.

• Jao, Chun-Sung; Marholm, Sigvald; Spicher, Andres & Miloch, Wojciech Jacek (2021). Wake formation behind Langmuir probes in ionospheric plasmas. Advances in Space Research. ISSN 0273-1177. 69(2), p. 856–868. doi: 10.1016/j.asr.2021.11.012. Full text in Research Archive Show summary

  This paper presents a simulation study of the wake formation behind a Langmuir probe thinner than the Debye Length in the space environments such as the ionosphere’s F region. We find that the wakes formed in plasma density and electric potential behind the positively biased probe can extend up to 15 Debye lengths in the subsonic plasma flow. Higher electric bias and flow velocity can further enhance the plasma wake perturbations. With an external magnetic field parallel to the object’s axis, the plasma wake becomes asymmetric and more extensive than for the unmagnetized case. The wing structures in the electron and ion densities are also observed along the background magnetic field in the case of subsonic plasma flow. The quantitative results in this paper may provide a practical reference for data processing and the future design of the Langmuir probe instrument flying in the F region on such as sounding rockets and low Earth orbit (LEO) satellite missions. In particular, since the Langmuir probe instrument may comprise two or more biased Debyescale Langmuir probes, the plasma wake formed behind a single probe may influence the measurements from other instruments onboard.

• Jin, Yaqi; Xiong, Chao; Clausen, Lasse Boy Novock; Spicher, Andres; Kotova, Daria & Brask, Steffen [Show all 9 contributors for this article] (2020). Ionospheric Plasma Irregularities Based on In Situ Measurements From the Swarm Satellites. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 125(7). doi: 10.1029/2020JA028103. Full text in Research Archive Show summary

  In this study, we present global climatological distributions of ionospheric plasma irregularities based on measurements by the Swarm satellites. These first global statistics obtained by direct, in situ measurements of plasma variations with Swarm confirm the presence of three main regions of strong ionospheric irregularities: the magnetic equator extending from postsunset to early morning, in the auroral ovals (from dayside cusp to nightside), and inside the polar caps. At equatorial latitudes, ionospheric irregularities form two bands of enhanced plasma fluctuations centered around ±10° magnetic latitude. Due to different plasma processes, ionospheric irregularities at high and low latitudes show different distributions. Though the averaged intensity of plasma irregularities is weaker at equatorial latitudes than at high latitudes, the occurrence rate of significant plasma fluctuations (corresponding to extreme events) is much higher at the equator than that at high latitudes. Equatorial irregularities display clear seasonal and longitudinal variations; that is, they are most prominent over South America during the December solstice and are located over Africa during the June solstice. The magnitude of ionospheric irregularities at all latitudes is strongly controlled by the solar activity. Ionospheric irregularities become significantly weaker after 2016 during the current declining phase of solar activity. The interplanetary magnetic field Bz modulates the occurrence of ionospheric irregularities at both high and low latitudes.

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• Mann, Ingrid; Olsen, Sveinung viggo; Eilertsen, Yngve; Yokoyama, Yoshihiro; Tinguely, Jean-Claude & Spicher, Andres [Show all 20 contributors for this article] (2026). Maxidusty-2: The SCIENCE AND CAMPAIGN OVERVIEW. Full text in Research Archive
• Mann, Ingrid; Olsen, Sveinung viggo; Eilertsen, Yngve; Yokoyama, Yoshihiro; Tinguely, Jean-Claude & Spicher, Andres [Show all 18 contributors for this article] (2026). Dust and ionospheric constituents measured in the MLT during noctilucent cloud conditions. Full text in Research Archive
• Mann, Ingrid; Olsen, Sveinung viggo; Eilertsen, Yngve; Yokoyama, Yoshihiro; Tinguely, Jean-Claude & Spicher, Andres [Show all 18 contributors for this article] (2026). MXD2 Science and Campaign Overview. Full text in Research Archive
• Mann, Ingrid; Olsen, Sveinung viggo; Eilertsen, Yngve; Yokoyama, Yoshihiro; Tinguely, Jean-Claude & Spicher, Andres [Show all 15 contributors for this article] (2026). Maxidusty-2 in-situ measurements and sample collection in NLC/PMSE layers. Full text in Research Archive
• Løkke, Andrea Dahlmo; Huyghebaert, Devin Ray; Kvammen, Andreas; Spicher, Andres; Yokoyama, Yoshihiro & Mann, Ingrid (2026). Towards a physical classification of meteor head echoes from long-term EISCAT VHF observations. Full text in Research Archive Show summary

  Cosmic dust entering Earth’s atmosphere ablates and produces particles that affect the atmosphere, but the entry and accumulation processes remain poorly understood. We introduce an ~1M event catalogue of meteor head echoes from vertical beam EISCAT VHF observations (2014–present), extracted using software developed by Huyghebaert et al. (2025). These echoes, produced by sub millimetre microgram meteoroids, are analysed via temporal and spatial evolution of SNR and line of sight Doppler velocity to partition events into five classes: ordinary ablation, differential ablation, fragmentation, ambiguous head echoes, and non head echo signals. A small subset of events is manually labelled to guide semi supervised classification of the full dataset. Preliminary results show clear clustering by radar signature, suggesting physically distinct populations. Statistical analyses of the labelled dataset may refine estimates of meteoroid composition and the processes governing atmospheric entry.

• Frøystein, Ingeborg; Spicher, Andres; Vierinen, Juha & Oksavik, Kjellmar (2026). A multi-instrument case study of the dayside ionospheric behavior under varying IMF conditions. Full text in Research Archive
• Løkke, Andrea Dahlmo; Huyghebaert, Devin Ray; Kvammen, Andreas; Spicher, Andres; Yokoyama, Yoshihiro & Mann, Ingrid (2026). Meteor head echoes observed with EISCAT VHF between 2014 and 2024. Full text in Research Archive Show summary

  Meteors are observed through their head echoes using the 224 MHz EISCAT VHF radar located at Ramfjordmoen near Tromsø, Norway (69.59◦N, 19.23◦E). These head echoes, produced by sub-millimetre meteoroids in the estimated microgram mass range, are detected within the 80 to 130 km altitude range for periods between 6-150 ms. In this study, we analyse meteor head echoes extracted from approximately 1500 hours of zenith-pointing EISCAT VHF measurements conducted since 2014. These measurements span different times of day and year, including periods of meteor showers. The head echoes are identified using an extraction software developed by D. Huyghebaert and J. Vierinen, yielding a dataset of approximately one million meteor head echo events. For each event, we examine the echo strength as a function of time and altitude, along with the Doppler line-of-sight velocity, which serves as the basis for classifying the head echoes. Events are categorized into five classes based on distinct temporal and spatial features in the echo strength and line-of-sight Doppler velocity. The first three classes are believed to correspond to specific meteor phenomena: ordinary ablation, differential ablation and fragmentation. The remaining two classes, ambiguous head echoes and non-head echoes, represent signals that either lack sufficient information for classification or are unrelated to known meteor phenomena. A small subset of the events is manually classified to support semi-supervised classification of the full dataset. Our preliminary results confirm that the head echo parameters cluster around characteristic signatures, and we discuss the potential links between these characteristics and meteoroid properties.

• Gavazzi, Etienne; Spicher, Andres; Gustavsson, Björn Johan; Clemmons, James H.; Rowland, Douglas E. & Vierinen, Juha (2026). Auroral electron acceleration by dispersive Alfvén waves – insights from the VISIONS-2 rocket mission. Full text in Research Archive Show summary

  Alfvén waves with small perpendicular scale lengths are dispersive and can carry parallel electric fields. In the Earth's magnetosphere, they capture and accelerate electrons in a resonant process along the magnetic field lines down into the high-latitude ionosphere. These wave-particle interactions are considered to be a significant driver of auroral particle acceleration and as such an important coupling process between the magnetospheric and ionospheric systems. However, studying these waves and their associated auroral precipitations remains challenging due to the short temporal and spatial scales involved. As a result, their role in auroral dynamics continues to be an active area of research. Here, we present data from one of the VISIONS-2 (Visualizing Ion Outflow via Neutral Atom Sensing-2) sounding rocket launched in December 2018 from Ny-Ålesund, Svalbard, in the active dayside auroral region. Numerous time-energy dispersed structures, indicative of particle acceleration by Alfvén waves, were observed by the top-hat ESA instrument. We present the high-resolution measurements of several of these structures and analyse their time-of-arrival in energy and pitch-angle. We discuss the implications of these observations for understanding the acceleration region.

• Yokoyama, Yoshihiro; Olsen, Sveinung viggo; Eilertsen, Yngve; Spicher, Andres; Tinguely, Jean-Claude & Ludacka, Ursula [Show all 11 contributors for this article] (2026). Initial results of the analysis of dust collected in the mesosphere by the MESS instrument during the Maxidusty-2 campaign. Full text in Research Archive
• Yokoyama, Yoshihiro; Olsen, Sveinung viggo; Eilertsen, Yngve; Spicher, Andres; Tinguely, Jean-Claude & Ludacka, Ursula [Show all 10 contributors for this article] (2026). Mesospheric dust studies with sample analysis and in-situ measurement from Maxidusty-2. Full text in Research Archive
• Yokoyama, Yoshihiro; Olsen, Sveinung viggo; Eilertsen, Yngve; Spicher, Andres; Tinguely, Jean-Claude & Ludacka, Ursula [Show all 11 contributors for this article] (2026). Estimation of mesospheric dust size distribution and direct investigation of dust composition with collected samples from the MXD-2 rocket campaign. Full text in Research Archive
• Frøystein, Ingeborg; Spicher, Andres; Oksavik, Kjellmar; Gustavsson, Björn Johan & Johnsen, Magnar Gullikstad (2026). Characterizing the dayside auroral ionosphere with ISR elevation scans and field-aligned observations. doi: 10.5194/egusphere-egu26-12983. Full text in Research Archive Show summary

  The dayside auroral ionosphere exhibits significant variability because of its strong coupling to the magnetosphere-solar wind system. Dayside aurora is typically driven by soft precipitation, which also produces enhanced electron temperatures at high altitudes and can be easily measured by Incoherent Scatter Radars. Using EISCAT Svalbard radar (ESR) fast elevation scans, we identify the equatorward boundary of the dayside aurora and extract near-simultaneous ionospheric altitude profiles within and outside the auroral region, allowing for an investigation of ionospheric behavior with respect to the relative distance from this boundary. In addition, the large data set of ESR field-aligned observations facilitates statistical analysis over two solar cycles. Together, both field-aligned observations and elevation scans contribute to a characterization of the dayside auroral ionosphere. 

• Spicher, Andres & Oksavik, Kjellmar (2025). Observing the cusp using Eiscat TRACERS-EISCAT campaigns. Full text in Research Archive
• Spicher, Andres (2025). On plasma turbulence in the polar regions. Full text in Research Archive
• Madhanakumar, Mahith; Spicher, Andres; Huyghebaert, Devin Ray; Kashcheyev, Anton; Spogli, Luca & Oksavik, Kjellmar [Show all 9 contributors for this article] (2025). Observations of irregularities with scales from 3 meters to several hundreds of kilometers during the May 2024 Superstorm | CEDAR. doi: https:/cedarscience.org/sites/default/files/2025-posters/irri-11-mahith-madhanakumar-poster-2.pdf. Full text in Research Archive
• Spicher, Andres (2025). On the characteristics of ionospheric density irregularities in the polar regions. Full text in Research Archive
• Spicher, Andres; Kvammen, Andreas; Zettergren, Matthew; Deschpande, Kshitija; Vaggu, Pralay R. & Vierinen, Juha (2025). On the nature of high-latitude ionospheric fluctuations associated with the Kelvin-Helmholtz Instability. Full text in Research Archive
• Frøystein, Ingeborg; Spicher, Andres; Oksavik, Kjellmar & Gustavsson, Björn Johan (2024). Identification and characterization of the dayside ionospheric low energy precipitation region based on ISR measurements. Full text in Research Archive
• Jin, Yaqi; Spicher, Andres; Pecseli, Hans Laszlo; Clausen, Lasse; Miloch, Wojciech Jacek & Jacobsen, Knut Stanley [Show all 9 contributors for this article] (2024). In-situ observations of plasma blob inside the nightside auroral region and features of small-scale irregularities. Full text in Research Archive
• Madhanakumar, Mahith; Spicher, Andres; Vierinen, Juha-Pekka; Oksavik, Kjellmar; Huyghebaert, Devin Ray & Martin, Carley J [Show all 7 contributors for this article] (2024). The progress and decay of GNSS scintillation during a weak geomagnetic storm: A case study. Full text in Research Archive
• Frøystein, Ingeborg; Spicher, Andres; Oksavik, Kjellmar & Gustavsson, Björn Johan (2024). On the Dynamics and IMF Effects in the Dayside Ionospheric Region Based on ISR Measurements. Full text in Research Archive
• Spicher, Andres; Kvammen, Andreas; Zettergren, Matthew David; Bonnell, John W.; Clausen, Lasse & Deshpande, Kshitija [Show all 14 contributors for this article] (2024). Understanding the creation of ionospheric F-region turbulence and its spatio-temporal evolution using GNSS scintillations, auxiliary instruments and modeling. Full text in Research Archive Show summary

  The high-latitude F-region ionosphere is highly dynamic due to its strong coupling with the solar wind and magnetosphere. As a consequence, plasma density fluctuations or “irregular turbulent” structures are regularly observed in that region. When spanning a few decameters to a few kilometers, these irregularities can cause rapid fluctuations or “scintillations” in radio signals such as those typically used for trans-ionospheric navigation and communication, including Global Navigation Satellite Systems (GNSS) or HF communication systems. This work is intended to advance our understanding of the creation of ionospheric F-region turbulence and its spatio-temporal evolution. We show observations of the ionospheric conditions related to the presence of scintillations in the dayside region using measurements from ground-based instruments such as the EISCAT radars, all-sky cameras, and GNSS receivers combined with in-situ measurements from satellites and sounding rockets. We evaluate the possible sources of free energy and the relevance of several instabilities to create the irregularities causing the scintillations observed for selected case events. We focus on density structures related to flow shears and take advantage of the multi-instrument observations as input parameters for numerical simulations. We use the Geospace Environment Model of Ion-Neutral Interactions (GEMINI) [1] to characterize the nature of density fluctuations associated with the Kelvin-Helmholtz instability, with focus on the non-linear regime. Modelling results show that KHI can grow within minutes and can generate structures that lead to significant scintillations [2]. Additionally, we study how the density fluctuations evolve and how the energy is re-distributed across the scales as the instability evolves, allowing to compare with observations. Finally, we discuss future modelling work and observations necessary to make progress in the field. [1] Zettergren, et al. (2015), Geophys. Res. Lett., 42, 10, doi:10.1002/2015GL066806. [2] Spicher, et al. (2020), J. Geophys. Res., 125, e2019JA027734. https://doi.org/10.1029/2019JA027734

• Madhanakumar, Mahith; Spicher, Andres; Vierinen, Juha-Pekka; Oksavik, Kjellmar; Coster, Anthea J. & Huyghebaert, Devin Ray [Show all 9 contributors for this article] (2024). On the asymmetry between scintillation intensity in the pre-noon and post-noon sectors. Full text in Research Archive
• Birkeland, Roger; Orlandic, Milica; Johansen, Tor Arne; Kohfeldt, Anja; Røed, Ketil & Berger, Tor [Show all 12 contributors for this article] (2024). An update on Norwegian Space Education. Full text in Research Archive
• Kvammen, Andreas; Spicher, Andres; Zettergren, Matthew David; Huyghebaert, Devin Ray; Rexer, Theresa & Gustavsson, Björn Johan [Show all 7 contributors for this article] (2024). Formation and evolution of the Kelvin-Helmholtz Instability in the Arctic Ionosphere. Full text in Research Archive
• Kvammen, Andreas; Spicher, Andres; Zettergren, Matthew David; Huyghebaert, Devin Ray; Rexer, Theresa & Gustavsson, Björn Johan [Show all 7 contributors for this article] (2024). Conditions for the Kelvin-Helmholtz Instability in the Polar Ionosphere. Full text in Research Archive
• Kvammen, Andreas; Vierinen, Juha-Pekka; Huyghebaert, Devin Ray; Rexer, Theresa; Spicher, Andres & Gustavsson, Björn Johan [Show all 7 contributors for this article] (2024). NOIRE-Net - A convolutional neural network for automatic classification and scaling of high-latitude ionograms. Full text in Research Archive
• Madhanakumar, Mahith; Spicher, Andres; Vierinen, Juha-Pekka & Oksavik, Kjellmar (2024). Multi-instrument study of dayside scintillation at GNSS L-band frequencies. Full text in Research Archive
• Spicher, Andres; Rexer, Theresa; Kvammen, Andreas; Madhanakumar, Mahith; Zettergren, M. & Oksavik, Kjellmar [Show all 11 contributors for this article] (2024). Characterization and Assessment of Structuring Connected to Auroral Dynamics using EISCAT_3D (CASCADE): A brief overview. Full text in Research Archive
• Spicher, Andres; Kvammen, Andreas; Zettergren, M.; Roglans, Roger; Bonnell, John W & LaBelle, James [Show all 20 contributors for this article] (2024). Characterizing ionospheric turbulence on the poleward side of the cusp using sounding rocket observations and modelling work. Full text in Research Archive
• Gavazzi, Etienne; Spicher, Andres; Gustavsson, Björn Johan; Clemmons, James H.; Pfaff, Robert F. & Rowland, Douglas E. (2024). Time-dependent electron transport calculations of small-scale dynamic precipitation. Full text in Research Archive
• Madhanakumar, Mahith; Spicher, Andres; Vierinen, Juha-Pekka & Oksavik, Kjellmar (2024). Source regions of irregularities causing GNSS radio scintillation: An investigation using EISCAT. Full text in Research Archive
• Gavazzi, Etienne; Spicher, Andres; Gustavsson, Björn Johan; Clemmons, James H.; Pfaff, Robert F. & Rowland, Douglas E. (2024). Combining Time-Dependent Electron Transport Calculations with Rocket Measurements to Study Small-Scale Dynamic Precipitation. Full text in Research Archive
• Ivarsen, Magnus Fagernes; Jin, Yaqi & Spicher, Andres (2024). What are the dominant causes of density irregularities in the ionospheric cusp. Full text in Research Archive
• Spicher, Andres; Vierinen, Juha-Pekka; Rexer, Theresa; Häggstrøm, Ingemar; Huyghebaert, Devin Ray & Gustavsson, Björn Johan [Show all 7 contributors for this article] (2024). On the characteristics of meso-scale ionospheric dynamics based on EISCAT radar low-elevation experiments. Full text in Research Archive
• Madhanakumar, Mahith; Spicher, Andres; Vierinen, Juha-Pekka; Oksavik, Kjellmar; Coster, Anthea J. & Huyghebaert, Devin Ray [Show all 9 contributors for this article] (2024). On the asymmetry between scintillation intensity in the pre-noon and post-noon sectors. Full text in Research Archive
• Huyghebaert, Devin Ray; Chau, Jorge L.; Spicher, Andres; Ivarsen, Magnus Fagernes; Clausen, Matthias & Latteck, Ralph [Show all 7 contributors for this article] (2023). Large Scale Temporal and Spatial Characteristics of E-region Plasma Irregularities Measured by SIMONe Norway. Full text in Research Archive
• Spicher, Andres; Steuwer, Axel; Huyghebaert, Devin Ray; Ogawa, Yasunobu; Vierinen, Juha & Stamm, Johann Immanuel [Show all 8 contributors for this article] (2023). EISCAT and EISCAT 3D Primer. Full text in Research Archive
• Spicher, Andres; Steuwer, Axel; Huyghebaert, Devin Ray; Ogawa, Yasunobu; Vierinen, Juha & Stamm, Johann Immanuel [Show all 8 contributors for this article] (2023). EISCAT 3D Status and Future Development. Full text in Research Archive
• Huyghebaert, Devin Ray; Gustavsson, Björn Johan; Vierinen, Juha-Pekka; Spicher, Andres; Kvammen, Andreas & Zettergren, Matthew D. (2023). EISCAT_3D Imaging Techniques for Ionospheric Incoherent Scatter Spectra Reconstruction. Full text in Research Archive
• Spicher, Andres (2023). Space physics at UiT The Arctic University of Norway, Tromsø. Full text in Research Archive
• Kvammen, Andreas; Spicher, Andres; Zettergren, Matthew D.; Huyghebaert, Devin Ray; Rexer, Theresa & Gustavsson, Björn Johan [Show all 7 contributors for this article] (2023). Conditions for the Kelvin-Helmholtz Instability in the Polar Ionosphere. Full text in Research Archive Show summary

  The polar ionosphere is highly structured with density irregularities observed at a wide range of scale sizes: small scale (< 1 km), meso-scale (1–100 km) and large scale (> 100 km). Plasma irregularities are of interest since they may disturb Global Navigation Satellite Systems (GNSS) signals and disrupt High Frequency (HF) communication. Still, the conditions for the formation, the energy cascading from large to small scales and the non-linear evolution of plasma instabilities that cause irregularities in the polar ionosphere are largely unknown. This poster focuses on examining one of the most commonly invoked instabilities at high latitudes: the Kelvin-Helmholtz instability. The Kelvin-Helmholtz instability can be excited when there exists a shear in the flow velocity. At polar latitudes, flow shears are often observed in relation to auroral arcs, flow channels and reverse flow events. In this work, we use the 3D Geospace Environment Model of Ion-Neutral Interactions (GEMINI) to simulate the Kelvin-Helmholtz instability under various ionospheric conditions. This allows us to characterize the conditions favorable for Kelvin-Helmholtz instability growth. The presented results can be used as a reference to better understand observations of density irregularities under turbulent conditions at high latitudes.

• Spicher, Andres (2023). Characterizing high-latitude ionospheric turbulence. Full text in Research Archive
• Spicher, Andres; Kvammen, Andreas; LaBelle, James; Zettergren, Matthew D.; Bonnell, John W. & Roglans, Roger [Show all 20 contributors for this article] (2023). Examining the relevance of different instability mechanisms in causing ionospheric cusp irregularities based on sounding rocket data and numerical simulations. Full text in Research Archive
• Gavazzi, Etienne; Spicher, Andres; Gustavsson, Björn Johan; Clemmons, James H.; Pfaff, Robert F. & Rowland, Douglas E. (2023). Time dependent electron transport calculations of the ionospheric response to Alfvénic precipitations. Full text in Research Archive
• Rexer, Theresa; Spicher, Andres; Kvammen, Andreas & Vierinen, Juha (2023). Characteristics of polar ionospheric plasma density irregularities with multi-point measurements. Full text in Research Archive
• Rexer, Theresa; Spicher, Andres; Vierinen, Juha & Kvammen, Andreas (2023). Exploring Characteristics of Turbulent Density Fluctuations in the Arctic Ionosphere with Multi-Point Measurements. Full text in Research Archive
• Buschmann, Lisa Marie; Spicher, Andres; Clausen, Lasse; Marholm, Sigvald & Miloch, Wojciech Jacek (2022). Role of particle precipitation on plasma structuring at different altitudes by in-situ measurements. Full text in Research Archive
• Spicher, Andres; LaBelle, James William; Bonnell, John W.; Roglans, Roger; Moser, Chrystal & Fuselier, Stephen A. [Show all 18 contributors for this article] (2022). Sounding rocket investigation of multi-scale (density) irregularities in the cusp region. Full text in Research Archive
• Mann, Ingrid; Olsen, Sveinung viggo; Eilertsen, Yngve; Trollvik, Henriette; Pinneau, Adrien & Palinkas, Sabina Strmic [Show all 11 contributors for this article] (2022). Plans for Mesospheric Dust Studies with MXD2. Full text in Research Archive
• Spicher, Andres; Vierinen, Juha; Oksavik, Kjellmar; Jin, Yaqi; Huyghebaert, Devin Ray & Madhanakumar, Mahith (2022). Multi-instrument multi-scale characterization of ionospheric irregularities in the cusp region. Full text in Research Archive
• Spicher, Andres (2022). High-latitude ionospheric density turbulence. Full text in Research Archive
• Spicher, Andres; Vierinen, Juha; Oksavik, Kjellmar & Jin, Yaqi (2022). Statistical characteristics of ionospheric irregularities in the cusp ionosphere based on multi-instrument techniques. Full text in Research Archive Show summary

  Plasma density irregularities disturbing signals from Global Navigation Satellite Systems (GNSS) are known to be regular features of the high-latitude ionosphere, especially around the cusp and auroral regions. Despite their relevance for society, irregularity formation and evolution are still relatively poorly understood, and observations revealing the spatio-temporal characteristics of ionospheric structuring at different scales are needed to assess the exact mechanism(s) responsible for them. In this study, we focus on data from the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radars (ESR) operating in fast scanning mode. We use ESR experiments in which the antenna was swept in elevation, and create consecutive two-dimensional images showing how electron density, ion velocity, electron temperature, and ion temperatures change with latitude and time at different altitudes. We present selected events in which the ESR scans are combined with all-sky images and in-situ data from the Swarm satellites to provide multi-scale observations of cusp phenomena comprising polar cap patches, flow channels, particle precipitation, and ion heating. We compare the observations with the presence of GNSS scintillations, allowing to monitor the onset and development of irregularities causing scintillations, and to inspect their connection with the phenomena above-mentioned. We then extend the analysis by performing a statistical study using all ESR fast scans identified between January 2001 and December 2015. We investigate the statistical characteristics of the measured parameters at different altitudes and under different geomagnetic conditions. Overall, this study will provide further insights onto the spatio-temporal evolution of ionospheric cusp dynamics, and on the possible physical sources causing ionospheric irregularities with Space weather impacts.

• Spicher, Andres; Moen, Jøran Idar; LaBelle, James William; Bonnell, John W; Roglans, Roger & Moser, Chrystal [Show all 18 contributors for this article] (2021). Sounding rocket studies of ionospheric turbulence above Svalbard. Full text in Research Archive Show summary

  Every morning between about 06 UT and 11 UT, Svalbard rotates just below the cusps (dayside aurora), where direct coupling between the solar wind, magnetosphere and ionosphere occurs. This provides a unique window to study the dayside aurora and the highly dynamic processes associated with it, examples of which include electron and ion precipitation and heating, electrostatic and electromagnetic waves, as well as turbulence. In this work, we focus on the turbulence which, alongside with being of pure scientific interest, can also have societal impacts. Indeed, the “irregular” electron density structures associated with it can affect our technology infrastructures by for instance degrading High Frequency (HF) communication and Global Navigation Satellite Systems (GNSS) signals. After briefly reviewing some of the mechanisms believed to be important in the development of turbulence in the high-latitude ionosphere, we present recent observations of density irregularities obtained by sounding rockets above Svalbard. We focus on measurements made as a part of the Grand Challenge Initiative (GCI) Cusp, an international project combining sounding rockets missions and ground-based instruments to study the cusps. We show detailed characterization of the nature of the irregularities including their phase velocity and wavelengths, helping shedding light onto the process(es) involved in their formation, especially at the scales important for Space weather applications.

• Mare, Francesca Di; Spicher, Andres; Clausen, Lasse; Miloch, Wojciech Jacek; Takahashi, Toru & Moen, Jøran Idar (2021). Turbulence and Intermittency in the Winter Cusp Ionosphere studied with the ICI Sounding Rockets. Full text in Research Archive
• Spicher, Andres & Vierinen, Juha (2021). On the spatio-temporal characteristics of cusp structuring using the EISCAT Svalbard radars in scanning mode. Full text in Research Archive
• Spicher, Andres; LaBelle, James William; Bonnell, John W; Bounds, Scott; Clausen, Lasse Boy Novock & Mare, Francesca Di [Show all 16 contributors for this article] (2020). On multi-scale density irregularities observed by sounding rockets within regions of enhanced scintillations in the cusp ionosphere. Full text in Research Archive
• Mare, Francesca Di; Spicher, Andres; Clausen, Lasse Boy Novock; Miloch, Wojciech Jacek & Moen, Jøran Idar (2020). Turbulent Signatures in the Polar Cusp Ionosphere using sounding rocket mission observations. Full text in Research Archive
• Mare, Francesca Di; Spicher, Andres; Clausen, Lasse Boy Novock; Miloch, Wojciech Jacek & Moen, Jøran Idar (2020). Turbulence Signatures in the Polar/Cusp Ionosphere based on ICI sounding rocket missions. Full text in Research Archive
• Spicher, Andres; Kletzing, Craig A.; Bounds, Scott; Bonnell, John W.; Roglans, Roger & Fuselier, Stephen A. [Show all 21 contributors for this article] (2020). Cusp rocket experiment of density structures. Full text in Research Archive
• Madhanakumar, Mahith & Spicher, Andres (2026). Ionospheric Plasma Structuring Across a Range of Scale Sizes and GNSS Scintillation During Different Geomagnetic Conditions. UiT Norges arktiske universitet. ISSN 9788282366717. Full text in Research Archive Show summary

  The purpose of this thesis is to expand the current knowledge on the ionospheric conditions during periods of GNSS scintillation and the associated structuring of plasma across different scale sizes in the high latitude ionosphere. Specifically, we developed a methodology in order to identify the presence of ionospheric irregularities within an ambient plasma. By applying the methodology to the dayside ionosphere, we observed GNSS phase scintillation to be predominantly associated with irregularities in the F-region. The associated plasma conditions revealed the presence of elevated electron and ion temperatures in the F-region. The observations therefore support the importance of cusp/auroral dynamics in producing irregularities that can perturb GNSS signals in the dayside ionosphere. We also conducted a multi-instrument study at the dayside polar ionosphere to understand the evolution of scintillation strengths during periods of quiet geomagnetic conditions. Intense amplitude and phase scintillation were observed simultaneously on multiple GNSS signals that persisted for more than one hour in duration. The associated ionospheric conditions revealed dense polar cap patches, co-located with regions of soft electron precipitation and ion Joule heating, to be an important source of plasma irregularities. Furthermore, it was observed that a reversal in the interplanetary magnetic field components, By and Bz , led to the formation of a region of depleted density in the polar ionosphere. This resulted in the significant weakening of irregularities at Fresnel and kilometer scales (and hence a reduction of amplitude and phase scintillation) in the post-noon sector. Furthermore, we also examined the progress and decay of irregularities and plasma structures with scale sizes from three meters to several hundreds of kilometers during the May 2024 superstorm. Simultaneous existence of irregularity scales from three meters to several kilometers were observed at the dayside auroral ionosphere during the storm’s expansion phase on 10 May. Intense irregularities existed for about four hours and were associated with dense plasma structures from sub-auroral latitudes and energetic particle precipitation. As the storm progressed, Fresnel irregularities and structures with scales of the order of several hundreds of kilometers remained at substantially weakened levels. On the other hand, intense three meter irregularities in the E-region and kilometer scale structures associated with GNSS phase fluctuations persisted for about 24 hours. In contrast to 10 May, the dayside auroral ionosphere on 11 May was depleted of irregularities across all scale sizes due to the lack of dense ionospheric plasma and energetic particle precipitation.

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