Sources of the high latitude ionosphere variability during winter nighttime

Abstract

The solar wind causes a continuous modulation of the high-latitude ionosphere, namely in the electric field, thermosphere heating, plasma transport, thermospheric composition and circulation. The main goal of this study is to investigate the mechanisms that play a role in the response of the ionosphere-thermosphere system to the variations in the solar wind and to quantify the response time regarding to different ionospheric regions. We use about twenty-five years of data provided by IGS Total Electron Content (TEC), and also EISCAT electron density and TEC, AISstorm atmospheric ionization rates generated by precipitating particles and Kan-Lee merging electric field Em obtained from OMNIWeb for our study. We chose Tromsø, Norway (69.58°N, 19.23°E) location for our analyses, as multiple data sources collocate there and can be paired to study the ionosphere conditions for long time periods. We investigate the response of the ionosphere to the solar wind variations during winter nighttime by using a lagged correlation method on IGS TEC and OMNI Em dataset, covering a 90 days period (1 January ± 45 days) between the years of 1998 and 2024. To identify the response of the different ionospheric regions and quantify their sources of the response, we select four EISCAT campaigns covering multiple days in the winter nighttime. EISCAT TEC is integrated and interpolated from the electron density profiles, for three separated regions in the ionosphere: 90-150 km (E-layer), 150-500 km (F-layer), and 90-500 km (both layers). We apply the same lagged correlation method between OMNI Em and EISCAT TEC for all campaigns. Our analyses show that the correlation between twenty-five years of IGS TEC and OMNI Em data in the auroral oval peaks at about ≈120 minutes time-lag. We observe two different ionospheric responses from the EISCAT campaigns: 1) driven by the E-region auroral particle precipitation (>keV) with ≈45-90 minutes of lag, and 2) driven by the F-region soft particle precipitation (a few hundred eV) during substorms and polar cap patches/blobs convected to the Tromsø location with ≈90-135 minutes of lag. Comparing the response times observed in the IGS and EISCAT datasets, we conclude that both auroral particle precipitation and convection processes that are taking place in the F-region are strongly controlling the persistent ionospheric response caused by the solar wind variations and modulating the ionosphere.