Variations in Ionospheric Peak Electron Density During Sudden Stratospheric Warmings in the Arctic Region

The focus of the paper is the ionospheric disturbances during sudden stratospheric warming (SSW) events in the Arctic region. This study examines the ionospheric behavior during 12 SSW events, which occurred in the Northern Hemisphere over 2006\textendash2013, based on vertical sounding data from DPS-4 ionosonde located in Norilsk (88.0\textdegreeE, 69.2\textdegreeN). Most of the addressed events show that despite generally quiet geomagnetic conditions, notable changes in the ionospheric behavior are observed during SSWs. During the SSW evolution and peak phases, there is a daytime decrease in NmF2 values at 10\textendash20\% relative to background level. After the SSW maxima, in contrast, midday NmF2 surpasses the average monthly values for 10\textendash20\ days. These changes in the electron density are observed for both strong and weak stratospheric warmings occurring at midwinter. The revealed SSW effects in the polar ionosphere are assumed to be associated with changes in the thermospheric neutral composition, affecting the F2-layer electron density. Analysis of the Global Ultraviolet Imager data revealed the positive variations in the O/N2 ratio within the thermosphere during SSW peak and recovery periods. Probable mechanisms for SSW impact on the state of the high-latitude neutral thermosphere and ionosphere are discussed.