Sigmund Guttu

• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Otterå, Odd Helge & Omrani, Nour-Eddine (2021). The 11 year solar cycle UV irradiance effect and its dependency on the Pacific Decadal Oscillation. Environmental Research Letters.  ISSN 1748-9326.  16 . doi: 10.1088/1748-9326/abfe8b Fulltekst i vitenarkiv. Vis sammendrag

  The stratospheric, tropospheric and surface impacts from the 11 year ultraviolet solar spectral irradiance (SSI) variability have been extensively studied using climate models and observations. Here, we demonstrate using idealized model simulations that the Pacific Decadal Oscillation (PDO), which has been shown to impact the tropospheric and stratospheric circulation from sub-decadal to multi-decadal timescales, strongly modulates the solar-induced atmospheric response. To this end, we use a high-top version of the coupled ocean–atmosphere Norwegian Climate Prediction Model forced by the SSI dataset recommended for Coupled Model Intercomparison Project 6. We perform a 24-member ensemble experiment over the solar cycle 23 in an idealized framework. To assess the PDO modulation of the solar signal, we divide the model data into the two PDO phases, PDO+ and PDO−, for each solar (maximum or minimum) phase. By compositing and combining the four categories, we hence determine the component of the solar signal that is independent of the PDO and the modulation of the solar signal by the PDO, along with the solar signal in each PDO phase. Reciprocally, we determine the PDO effect in each solar phase. Our results show that the intensification of the polar vortex under solar maximum is much stronger in the PDO− phase. This signal is transferred into the troposphere, where we find a correspondingly stronger polar jet and weaker Aleutian Low. We further show that the amplification of the solar signal by the PDO− phase is driven by anomalous meridional advection of solar-induced temperature anomalies over northern North America and the North Pacific, which contributes to a decreased meridional eddy heat flux and hence to a decreased vertical planetary wave flux into the stratosphere.

• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Limpasuvan, Varavut & Marsh, Daniel R. (2020). WACCM simulations: Decadal winter-to-spring climate impact on middle atmosphere and troposphere from medium energy electron precipitation. Journal of Atmospheric and Solar-Terrestrial Physics.  ISSN 1364-6826.  209 . doi: 10.1016/j.jastp.2020.105382 Fulltekst i vitenarkiv. Vis sammendrag

  Energetic particle precipitation is one of the main processes by which the sun influences atmospheric composition and structure. The polar middle atmosphere is chemically disturbed by the precipitation-induced production of nitric oxides (NOx) and hydrogen oxides (HOx) and the associated ozone (O3) loss, but the importance for the dynamics is still debated. The role of precipitating medium energy electrons (MEEs), which are able to penetrate into the mesosphere, has received increased attention, but has only recently begun to be incorporated in chemistry-climate models. We use the NCAR Whole Atmosphere Community Climate Model (WACCM) to study the climate impact from MEE precipitation by performing two idealized ensemble experiments under pre-industrial conditions, with and without the MEE forcing, over the period of the solar cycle 23 (only full calendar years, 1997–2007). Each experiment includes 20 11-year ensemble members, total 220 years. Our results indicate a strong month-to-month variability in the dynamical response to MEE throughout the winter period. We find a strengthening of the polar vortex in the northern hemisphere during December, but the signal decays rapidly in the following months. The polar vortex strengthening is likely attributable to planetary wave reduction due to increased zonal symmetries in upper stratospheric ozone heating, initially triggered by MEE-induced NOx advected into the sunlit regions. We also find a similar early winter polar vortex strengthening in the southern hemisphere during June. Changes in mean meridional circulation accompany these anomalous wave forcings, leading to dynamically-induced vertical temperature dipoles at high latitudes. The associated weakening of the stratospheric mean meridional circulation results in an upper stratospheric polar ozone deficit in early winter. This polar cap ozone deficit is strongest in the southern hemisphere and contributes to a polar vortex weakening in late winter, in concert with increased planetary wave forcing. In both hemispheres, the stratospheric polar vortex signal seems to migrate downwards into the troposphere and to the surface.

• Graff, Lise Seland; Guttu, Sigmund & Lacasce, Joseph Henry (2015). Relative dispersion in the atmosphere from reanalysis winds. Journal of the Atmospheric Sciences.  ISSN 0022-4928.  72(7), s 2769- 2785 . doi: 10.1175/JAS-D-14-0225.1

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• Orsolini, Yvan J.; Guttu, Sigmund & Stordal, Frode (2021). Impact of Medium-Energy Electron Precipitation on the Middle Atmosphere and on Climate in Decadal Simulations.
• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Limpasuvan, Varavut & Marsh, Daniel R. (2020). Impact of Medium-Energy Electron Precipitation on Ozone and Middle Atmosphere Dynamics in WACCM Simulations.
• Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Otterå, Odd Helge; Toniazzo, Thomas & Verronen, Pekka T. (2020). Effects of the 11-year Solar Cycle including Medium-Energy Electron Precipitation in WACCM decadal climate predictions.
• Guttu, Sigmund & Orsolini, Yvan (2019). Impact of Medium-energy Electron Precipitation on Ozone and Middle Atmosphere Dynamics in WACCM simulations.
• Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Limpasuvan, Varavut & Marsh, D. (2019). Impact of medium-energy electron precipitation on ozone and middle atmosphere dynamics in WACCM simulations.
• Orsolini, Yvan; Guttu, Sigmund; Stordal, Frode & Limpasuvan, Varavut (2019). Impact of Medium-energy Electron Precipitation on Ozone and Middle Atmosphere Dynamics in WACCM Simulations.
• Låg, Marit; Refsnes, Magne Arnold; Schwarze, Per Everhard; Landvik, Nina; Maass, Christine; Øvrevik, Johan; Holme, Jørn Andreas; Totlandsdal, Annike; Guttu, Sigmund & Melsom, Karin Elisabeth (red.) (2013). Luftkvalitetskriterier : virkninger av luftforurensning på helse. rapport Nasjonalt folkehelseinstitutt. 2013:9. Fulltekst i vitenarkiv.

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