Ionospheric studies based on geostationary satellite observations from Guwahati

Abstract

Ionospheric electron content ( IEC ) studies have been made from a low-midlatitude station, Guwahati, using radio beacon of the geostationary satellite ETS-II for a high solar activity period from June 1980 through December 1981. The study is first of its kind from the location. Diurnal behaviour of IEC for the period has been critically examined. IEC is found to start growing from a pre-dawn minimum and shows a steep growth with sunrise. It shows multiple growth rates - the highest being from 10-11 hr LT. At about 14 hr LT, IEC reaches the diurnal maximum value. Low depth bite-out effects in noontime IEC are observed on some occasions, and its occurrence is found to be maximum in summer. Sometimes, signatures of medium scale TIDs are also seen on the daytime IEC profiles. Occurrence of such TIDs are found to be maximum in winter, and interestingly they have maximum occurrence on days having geomagnetic index Ap in a range from 6 to 10. Small evening IEC enhancements of maximum occurrence in the equinoctial months, have also been observed at around 20 hr LT. Anomalous night enhancements, quite small in magnitude, are noticed around midnight, and they are seen more often in summer. The diurnal range of IEC shows annual variation - maximum of 16 in autumn and minimum of 5 in summer. IEC peak values show semiannual variation with strong seasonal anomaly - winter values being considerably higher than that of summer. The anomaly is found to be absent in midnight IEC, while diurnal minimum value of IEC shows annual variation - having its highest values during summer months and smallest in autumn. Studies on the integrated production rate ( Qo ) of IEC reveal strong seasonal anomaly in this parameter, - minimum values are observed in summer and highest in winter. The initial zenith angle of sun for ionization production is found to be highest in winter and lowest in summer indicating the predominance of atomic oxygen as the main absorber of solar radiation in all seasons except summer, for the observation period. The...