Research Article

Sources of the high latitude ionosphere variability during winter nighttime

¹ Institute for Solar-Terrestrial Physics, German Aerospace Center (DLR), Neustrelitz, Germany
² Institute of Geodesy and Geoinformation (IGG), University of Bonn, Bonn, Germany
³ Space Physics and Astronomy, University of Oulu, Oulu, Finland

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 30 September 2025
Accepted: 2 May 2026

Abstract

Solar wind energy is continuously deposited in the magnetosphere-ionosphere-thermosphere system, causing significant modifications primarily in the high latitude ionosphere. These variations are reflected most instantaneously in the ionospheric electron density (N_e) or in the total electron content (TEC). The drivers of ionospheric variability at high latitudes are not yet fully understood. This variability due to solar wind-magnetosphere-ionosphere coupling could be investigated under winter conditions, while ionization from EUV radiation is minimal, and ionization mostly comes from the coupling processes. This study characterizes the contributions of ionospheric drivers to winter TEC variability. We present a quantitative evaluation of the respective impact of the convection and particle precipitation processes on the TEC variability. We use comprehensive datasets of IGS and EISCAT TEC measurements, alongside merging electric field (E_m) calculated from solar wind parameters. We apply a lagged correlation method covering the wintertime to assess the temporal and spatial characteristics of ionospheric response. EISCAT UHF Incoherent Scatter Radar campaigns that consist of several days of continuous measurements are used to estimate the ionospheric response time to the solar wind in the E- and F-region separately and to identify the relevant coupling processes. Our results reveal that the highest correlation between IGS TEC and E_m is at a lag time of ≈2 h. The EISCAT results show distinctions between the E- and F-region ionosphere responses. In the E-region ionosphere, shorter delays of ≈71 min are observed. We suggest that the E-region TEC is driven by auroral particle precipitation during substorm processes, and the delay can be attributed to the loading and unloading times of the magnetosphere. In the F-region, the delays are longer with ≈101 min, indicating the effect of polar cap plasma convection, because this duration matches well with the duration of quiet time plasma convection across the polar cap. Under certain conditions, where the F-region is driven by dense polar cap patches and associated convection features, the delay in the F-region can be as short as 90 min. We find that the overall TEC response of ≈2 h originates mainly due to the F-region processes, where the electron density is modulated strongly by the convection of the plasma.