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Ann. Geophys., 20, 1843-1850, 2002
www.ann-geophys.net/20/1843/2002/
© European Geosciences Union 2002
A comparative study of night-time enhancement of TEC at a low latitude station on storm and quiet nights including the local time, seasonal and solar activity dependence
K. Unnikrishnan1,*, R. Balachandran Nair2, and C. Venugopal3
1School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam – 686 560, Kerala, India
2Department of Physics, College of Engineering, Kasargode – 671 541, Kerala, India
3Department of Physics, University of Asmara, P O Box 1220, Asmara, Eritrea
*Present Address: Department of Physics, N. S. S. Hindu College, Changanacherry – 686 102, Kerala, India
Correspondence to: K. Unnikrishnan
(kaleekkalunni@yahoo.com)
Abstract. The main characteristics
of night-time enhancements in TEC during magnetic storms are compared with
those during quiet nights for different seasons and solar activity conditions
at Palehua, a low latitude station during the period 1980–1989. We find that
the mean amplitude has both a seasonal and solar activity dependence: in
winter, the values are higher for weak storms as compared to those during quiet
nights and increase with an increase in solar activity. In summer, the mean
amplitude values during weak storms and quiet nights are almost equal. But
during equinox, the mean amplitude values for quiet nights are greater than
those during weak storms. The mean half-amplitude duration is higher during
weak storms as compared to that during quiet nights in summer. However, during
winter and equinox, the durations are almost equal for both quiet and weak
storm nights. For the mean half-amplitude duration, the quiet night values for
all the seasons and equinoctial weak storm values increase with an increase in
solar activity. The occurrence frequency (in percent) of TEC enhancement during
weak storms is greater than during quiet nights for all seasons. The mean
amplitude, the mean half-amplitude duration and the occurrence frequency (in
percent) of TEC enhancement values are higher during major storms as compared
to those during quiet nights. The above parameters have their highest values
during pre-midnight hours. From the data analysed, this behaviour is true in
the case of major storms also.
Key words. Ionosphere (ionospheric disturbances;
plasma convection) Magnetospheric physics (storms and substorms)
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