Long term ionospheric electron content variations over Delhi

Abstract

Abstract. Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91°E; dip Latitude 24.8°N), India, for the period 1975±80 and 1986± 89 belonging to an ascending phase of solar activity during ®rst halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IEC max (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IEC max shows positive correlation with F 10.7 up to about 200 ux units at equinox and 240 units both in winter and summer; for greater F 10.7 values, IEC max is substantially constant in all the seasons. IEC max and magnetic activity (A p ) are found to be positively correlated in summer in high solar activity. Winter IEC max shows positive correlation with A p in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IEC max is independent of A p in both solar cycles in low solar activity. A study of day-to-day variations in IEC max shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation.

TEC variations during low solar activity period (2005–2007) near the Equatorial Ionospheric Anomaly Crest region in India

“…Therefore, in order to get better positional accuracy, it is necessary to have a precise knowledge of the accurate value and the variations of the TEC at different geographical locations and under different geophysical conditions. TEC variations with local time, season, and solar activity has been studied extensively over the past few decades (Rastogi et al, 1971;da Rosa et al, 1973;Van Velthoven, 1990;Feitcher and Leitinger, 1997;Warnant et al, 2000;Gupta and Singh, 2000;Wu et al, 2008). In the past three decades, several individual measurements of TEC at various locations in India have been made using the available low earth orbiting satellites as well as geostationary satellites (Rastogi and Sharma, 1971;DasGupta and Basu, 1973;Rastogi et al, 1975;Rama Rao et al, 1977;Davies at el., 1979).…”

Faraday polarization fluctuations and their dependence on post sunset secondary maximum and amplitude scintillations at Delhi

“…However, Correspondence to: L. Singh (laksingh@csnpl.ren.nic.in) in addition to the daytime maximum around 14:00 IST, IEC shows enhancement after sunset during high solar activity. This phenomenon is generally called post sunset secondary maximum (PSSM) and has been studied at equatorial and low-latitudes by Tyagi et al (1982), Lakha Singh (1990a) and Gupta and Singh (2000).…”

Solar control of ambient ionization of the ionosphere near the crest of the equatorial anomaly in the Indian zone

“…Most of the workers (Balan et al, 1993;Gupta and Sing, 2001) obtained a linear relationship between the TECmax and the F10.7 for solar flux values up to about 200 flux units. Gupta and Singh (2001), considering TEC data from Delhi for the rising phases of the 21st and 22nd solar cycles, found the saturation effect at different seasons with a nonlinear fit. Present observations support the saturation-like effect only for a few months of the descending phase -this may be due to the peculiar position of the observing station relative to the equatorial anomaly crest.…”

“…An estimate of the equatorial electric field responsible for the fountain effect may be obtained from the electrojet strength. To extract the quantitative contribution of the transport mechanism, further investigation based on electrojet data is essential (Rastogi and Rajaram, 1971;Rush and Richmond, 1973;Sethia et al, 1980;Gupta and Singh, 2001). Sometimes the saturation-like effect is observed in the noon time diurnal TEC variation, as shown in Fig.…”

“…The peculiarity of the database is that it contains both the descending (1979)(1980)(1981)(1982)(1983)(1984)(1985) and ascending (1986-1990) phases of the solar cycles. The solar activity dependent features have been discussed in various papers (Golton and Walker, 1971;Rastogi and Sharma, 1971;Huang et al, 1989;Klobuchar et al, 1991;Prasad and Rama Rao, 1993;Feichter and Leitinger, 1997;Gupta and Singh, 2001;Jayachandran et al, 2004;Wu et al, 2004). These are mostly based on data for one solar cycle or less, or observations were made from mid/higher latitude regions.…”