Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

Abstract

Abstract. The seasonal e ects in the thermosphere and ionosphere responses to the precipitating electron¯ux and ®eld-aligned current variations, of the order of an hour in duration, in the summer and winter cusp regions have been investigated using the global numerical model of the Earth's upper atmosphere. Two variants of the calculations have been performed both for the IMF B y < 0. In the ®rst variant, the model input data for the summer and winter precipitating¯uxes and ®eld-aligned currents have been taken as geomagnetically symmetric and equal to those used earlier in the calculations for the equinoctial conditions. It has been found that both ionospheric and thermospheric disturbances are more intensive in the winter cusp region due to the lower conductivity of the winter polar cap ionosphere and correspondingly larger electric ®eld variations leading to the larger Joule heating e ects in the ion and neutral gas temperature, ion drag e ects in the thermospheric winds and ion drift e ects in the F2-region electron concentration. In the second variant, the calculations have been performed for the events of 28±29 January, 1992 when precipitations were weaker but the magnetospheric convection was stronger than in the ®rst variant. Geomagnetically asymmetric input data for the summer and winter precipitating¯uxes and ®eld-aligned currents have been taken from the patterns derived by combining data obtained from the satellite, radar and ground magnetometer observations for these events. Calculated patterns of the ionospheric convection and thermospheric circulation have been compared with observations and it has been established that calculated patterns of the ionospheric convection for both winter and summer hemispheres are in a good agreement with the observations. Calculated patterns of the thermospheric circulation are in a good agreement with the average circulation for the Southern (summer) Hemisphere obtained from DE-2 data for IMF B y < 0 but for the Northern (winter) Hemisphere there is a disagreement at high latitudes in the afternoon sector of the cusp region. At the same time, the model results for this sector agree with other DE-2 data and with the ground-based FPI data. All ionospheric and thermospheric disturbances in the second variant of the calculations are more intensive in the winter cusp region in comparison with the summer one and this seasonal di erence is larger than in the ®rst variant of the calculations, especially in the electron density and all temperature variations. The means that the seasonal e ects in the cusp region are stronger in the thermospheric and ionospheric responses to the FAC variations than to the precipitation disturbances.

Spatio‐Temporal Evolution of Global Ionospheric Storm Drivers and Hemispherical Asymmetry During 17–18 March 2015 Geomagnetic Storm

“…The thermospheric (O)/(N 2 ) ratio depletion, especially in the Asian sector, is apparent from Figure 8. Joule heating of the upper polar neutral atmosphere from enhanced storm time FACs and increased particle precipitation, cause storm time neutral winds which could transport N 2 molecules from the lower atmosphere to higher altitudes, consequently magnification of recombination rate in the F region and thus the (O)/(N 2 ) ratio decreased, leading to negative ionospheric storm (Anderson et al., 1998; Namgaladze et al., 1998).…”

The Global Numerical Model of the Earth’s Upper Atmosphere

“…This allows the modeling of the upper atmospheric behavior during substorms via the UAM simulations. The results were presented in [4,[48][49][50][51][52][53] including the cusp and auroral oval behavior, energetic magnetospheric electron precipitations, electric fields, current wedge and internal atmospheric gravity waves generation. The main role of the thermospheric heating due to the soft electron precipitation was shown for the thermosphere substorm effects.…”

Impact of seasonal variations on low and mid-latitudes ionospheric electric field satellite measurements

“…Thus, this field is influenced by various factors such as solar wind, Earth's magnetic field, and atmospheric winds. In the summer and winter cusp regions, it is found that ionospheric disturbances are more intensive in the winter cusp region, associated to higher electric field variations and electron flux precipitation [13]. During quiet periods, changes in the Sun's direction incorporated in the conductivity model indicates that the peak of the electric field at sunset is highest during the equinox and significant during the solstices.…”