Characteristics of VHF radiowave scintillations over a solar cycle (1983−1993) at a low-latitude station: Waltair (17.7°N, 83.3°E)

P V S Rama Rao,P T Jayachandran,B V Ramana Rao,D S V V D Prasad,K K Bose,P Sri Ram

doi:10.1007/s00585-997-0729-3

Abstract

Abstract. The characteristics of VHF radiowave scintillations at 244 MHz (FLEETSAT) during a complete solar cycle (1983–93) at a low-latitude station, Waltair (17.7°N, 83.3°E), are presented. The occurrence of night-time scintillations shows equinoctial maxima and summer minima in all the epochs of solar activity, and follows the solar activity. The daytime scintillation occurrence is negatively correlated with the solar activity and shows maximum occurrence during the summer months in a period of low solar activity. The occurrence of night-time scintillations is inhibited during disturbed days of high solar activity and enhanced during low solar activity.

Highlights

Man's interest in the ionosphere developed largely because of ionospheric communications, the improvement of which depends upon increased knowledge on short- and long-term behaviour of the ionosphere
This paper presents, for the ®rst time in the Indian sector, the continuous and long-term behaviour of the VHF radiowave scintillations at a low-latitude station over a complete solar cycle period (1983±1993)
Rama Rao et al.: Characteristics of VHF radiowave scintillations over a solar cycle (1983±1993) at a low-latitude station 731 solar activity (1989±1990)

Summary

Introduction

Man's interest in the ionosphere developed largely because of ionospheric communications, the improvement of which depends upon increased knowledge on short- and long-term behaviour of the ionosphere. Studies of solar-cycle variation of ionospheric irregularities that produce scintillations help a long way in planning transionospheric communication systems. The occurrence of equatorial scintillations has revealed a puzzling pattern that appears to vary both with season and longitude (Aarons, 1977; Basu and Basu, 1981). Besides the dierence in the seasonal behaviour among the observing stations, satellite and multistation observations have revealed distinct longitudinal variations in the occurrence during a given season (Sharma and Meldrew, 1975; Aarons et al, 1980). This paper presents, for the ®rst time in the Indian sector, the continuous and long-term behaviour of the VHF radiowave scintillations at a low-latitude station over a complete solar cycle period (1983±1993). The data have been grouped into three seasons as follows. (1) Equinox: March, April, September and October, (2) Winter: November, December, January and February. (3) Summer: May, June, July and August

Seasonal variation of night-time scintillations

Solar-cycle variation of night-time scintillations

Daytime scintillations

Discussion and conclusions