Sources of the high latitude ionosphere variability during winter nighttime

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 (Ne) or in the total electron content (TEC). The drivers of the ionospheric variability, at high latitudes, are yet not fully understood. This variability due to solar wind-magnetosphere-ionosphere coupling could be investigated under winter conditions while ionization from to EUV radiation is minimal and ionization mostly comes from the coupling processes. This study characterizes the contribution of the ionosphere drivers to the 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 with merging electric field (Em) calculated from solar wind parameters. We apply a lagged correlation method covering the winter time 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 Em is at a lag time of ≈2 hours. The EISCAT results show distinctions between the E- and F-region ionosphere responses. In the E-region ionosphere, shorter delays of ≈71.25 minutes 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 ≈101.25 minutes, 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-minutes. We find that the overall TEC response of ≈2 hours originates mainly due to the F-region processes, where the electron density is modulated strongly by the convection of the plasma.