A comprehensive investigation of Sudden Stratospheric Warming (SSW) events and upper atmospheric signatures associated with them

Abstract

We present a study of the major and minor SSWs that have occurred in the Northern Hemisphere (NH) over the past four decades (1981–2020) from a statistical perspective. This study investigates the frequency and timing of occurrence of major and minor SSWs during the specified period. A correlation is observed between the timing of the earliest minor SSWs and final events, having different correlation coefficients in all four decades, with minimum correlation during the decade 2001–2010, including the extended solar minima. In the second part of our work, we examined SSW events of the last 18 winters based on ERA5 and MERRA2 reanalysis data. Surprisingly, the stratospheric parameters have been found to show different behaviors depending on the number of SSW events in a winter. The temperature and zonal mean zonal wind variations are stronger during winters with one major SSW, rather than winters having major SSW accompanied by minor SSWs. Finally, we conducted four case studies to investigate the atmospheric and ionospheric response to major and minor SSWs over three stations, namely Okinawa (26.21°N,127.68°E), Yamagawa (35.45°N,133.62°E), and Wakkanai (45.16°N,141.75°E). Like the stratospheric parameters, ionospheric parameters are not found to be much depended on the number of SSWs in a winter, but they are found to vary from event to event. Significant latitudinal variations in ionospheric parameters were observed in all the events, with more pronounced effects toward lower latitudinal station Okinawa. Although ionospheric disturbances are more pronounced during major SSWs, some severe minor events also have notable ionospheric impacts just as the major SSW.