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Ann. Geophys., 16, 1283-1298, 1998
www.ann-geophys.net/16/1283/1998/
© European Geosciences Union 1998
Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region
A. A. Namgaladze1,2, A. N. Namgaladze2, and M. A. Volkov1,2
1Murmansk State Technical University, 13 Sportivnaya St., Murmansk, 183010, Russia (namgaladze@mstu.edu.ru)
2Polar Geophysical Institute, 15 Halturina St., Murmansk, 183010, Russia (namgalad@polar.murmansk.su)
Abstract. The seasonal effects in the thermosphere and
ionosphere responses to the precipitating electron flux and field-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 By < 0. In the first variant,
the model input data for the summer and winter precipitating fluxes and
field-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 field variations
leading to the larger Joule heating effects in the ion and neutral gas
temperature, ion drag effects in the thermospheric winds and ion drift effects
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 first
variant. Geomagnetically asymmetric input data for the summer and winter
precipitating fluxes and field-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 By
< 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 difference is larger than in
the first variant of the calculations, especially in the electron density and
all temperature variations. The means that the seasonal effects in the cusp
region are stronger in the thermospheric and ionospheric responses to the FAC
variations than to the precipitation disturbances.
Key words. Ionosphere (ionosphere · atmosphere
interactions; ionosphere · magnetosphere interactions; ionospheric
disturbances).
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