Abstract
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)
Highlights
It is well known that the total electron content (TEC) of the ionosphere does not decrease throughout the night as predicted by simple theory but shows anomalous enhancements
Mean half-amplitude duration and mean occurrence frequency of TEC enhancement values are higher during major storms as compared to those during quiet nights
The results presented here for quiet nights are consistent with similar studies: previous studies (Young et al, 1970; Balan et al, 1986, 1991) observed that the occurrence frequency of TEC enhancement, amplitude and half-amplitude duration all had a high positive correlation with solar activity at low latitudes, especially for quiet nights
Summary
It is well known that the total electron content (TEC) of the ionosphere does not decrease throughout the night as predicted by simple theory but shows anomalous enhancements. Lanzerotti et al (1975) studied the latitudinal dependence of the changes in the ionospheric TEC during 12 magnetic storms by considering stations Hamilton and Arecibo. We analysed all the night-time enhancement parameters like amplitude, half-amplitude duration and occurrence frequency (in percent) of TEC enhancement during 212 magnetic storms at Palehua for a period of 10 years from 1980– 1989 and their seasonal, solar activity and local time dependence were compared with those of quiet nights. We find that, during all the seasons, the occurrence frequency (in percent) of TEC enhancement during weak storms are greater than those during quiet nights. Mean half-amplitude duration and mean occurrence frequency (in percent) of TEC enhancement values are higher during major storms as compared to those during quiet nights
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