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• Follestad, Anna Kristine Fæhn; Clausen, Lasse; Moen, Jøran Idar & Jacobsen, Knut Stanley (2021). Latitudinal, Diurnal, and Seasonal Variations in the Accuracy of an RTK Positioning System and Its Relationship With Ionospheric Irregularities. Space Weather. ISSN 1542-7390. 19(6). doi: 10.1029/2020SW002625. Full text in Research Archive
• Follestad, Anna Kristine Fæhn; Clausen, Lasse Boy Novock; Miloch, Wojciech Jacek; van den IJssel, J. & Haagmans, Roger (2020). Two-Dimensional Reconstruction of Ionospheric Plasma Density Variations Using Swarm. Space Weather. ISSN 1542-7390. 18. doi: 10.1029/2019SW002406. Full text in Research Archive
• Follestad, Anna Kristine Fæhn; Herlingshaw, Katie; Ghadjari, Hossein; Knudsen, David J.; McWilliams, Kathryn A. & Moen, Jøran Idar [Show all 9 contributors for this article] (2020). Dayside Field-Aligned Current Impacts on Ionospheric Irregularities. Geophysical Research Letters. ISSN 0094-8276. 47(11). doi: 10.1029/2019GL086722. Full text in Research Archive Show summary

  Global Navigation Satellite Systems (GNSS) are subject to disturbances caused by plasma irregularities in the ionosphere. Studies have suggested that in addition to the gradient drift and Kelvin‐Helmholtz instabilities, electron precipitation may be important for phase scintillations in the dayside auroral region. This study combines in situ Swarm data with ground GNSS observations to investigate the potential role of filamentary field‐aligned currents (FACs) on phase scintillations in the dayside auroral region by analyzing 22 events with phase scintillations exceeding 0.45 radians. We observe colocation between regions of severe phase scintillations and highly filamented FACs with fluctuations measured in the spacecraft frame of the order of 20 Hz. The observations indicate that filamentary FACs are crucial drivers for irregularities responsible for creating severe phase scintillations measured in the dayside auroral region and are thus of significant importance in the context of space weather impact on satellite communication.

• Follestad, Anna Kristine Fæhn; Clausen, Lasse Boy Novock; Thomas, E.G.; Jin, Yaqi & Coster, A. (2019). Polar cap patch prediction in the expanding contracting polar cap paradigm. Space Weather. ISSN 1542-7390. 17(11), p. 1570–1583. doi: 10.1029/2019SW002276. Full text in Research Archive

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• Follestad, Anna Kristine Fæhn; Herlingshaw, Katie; Ghadjari, Hossein; Knudsen, David J.; McWilliams, Kathryn A. & Moen, Jøran Idar [Show all 9 contributors for this article] (2019). Birkeland Current Impacts on Cusp Ionospheric Irregularities. Show summary

  Global Navigation Satellite System (GNSS) scintillations at high latitudes have traditionally been attributed to the Gradient Drift Instability (GDI) associated with polar cap patches and flow shear instabilities such as the Kelvin-Helmholtz Instability (KHI). Previous studies have also shown that electron precipitation may play an important role for scintillations in the cusp. In this study, we combine in situ Swarm data with GNSS observations from a network of three ground based receivers around Svalbard, Norway, to further investigate the role of particle precipitation on phase scintillations in the cusp region. In particular, we examine the relation between strong scintillations and finely structured Birkeland currents. For this purpose, we identified 23 events in the winter time cusp with phase scintillations >0.45 radians. We show consistent colocation between enhanced cusp scintillations and regions of filamented Birkeland currents. In addition, we relate the observations to the presence of turbulence and dispersive Alfvén waves. The observations suggest that the filamentary field aligned currents and related particle precipitations in themselves together may act as the primary driver for the creation of irregularities responsible for ground based phase scintillations measured underneath the cusp.

• Follestad, Anna Kristine Fæhn (2020). Forecasting Space Weather Effects on GNSS Systems. Det matematisk naturvitenskapelige fakultet.

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