Abstract
Abstract. Electron temperature Te observed by the SROSS C2 satellite at equatorial and low latitudes during the low to high solar activity period of 1995–2001 at the height of ~500 km is investigated in terms of local time, season, latitude, solar sunspot number Rz and F10.7 cm solar flux. The satellite covered the latitude belt of 31° S–34° N and the longitude range of 40°–100° E. The average nighttime (20:00–04:00 LT) Te varies between 750–1200 K and then rises sharply in the sunrise period (04:00–06:00 LT) to the morning high from 07:00 to 10:00 LT and attains a daytime (10:00–14:00 LT) average of 1100–2300 K. The morning enhancement is more pronounced in the equinoxes. A secondary maximum in Te is also observed around 16:00–18:00 LT in the June solstice and in the equinoxes. Daytime electron temperature was found to be higher in autumn compared to that in spring in all latitudes. Between the solstices, the amplitude of the morning enhancement is higher in winter compared to that in summer. Both day and nighttime Te observed by the SROSS C2 satellite bears a positive correlation with solar activity when averaged on a shorter time scale, i.e. over the period of a month. But on a longer time scale, i.e. averaged over a year, the daytime electron temperature gradually decreases from 1995 till it reaches the minimum value in 1997, after which Te again continues to rise till 2001. The variations are distinctly seen in summer and in the equinoxes. The sunspot activity during solar cycle 23 was minimum in 1996 and maximum in 2000. Annual average electron temperature, therefore, appears to follow the variation of solar activity with a time lag of about one year, both at the bottom and top of solar cycle 23, indicating an inherent inertia of the ionosphere thermosphere regime to variations in solar flux.
Highlights
Experimental and theoretical study of electron temperature gives insight into the energy balance of the ionosphereplasmasphere regime
Both day and nighttime Te observed by the SROSS C2 satellite bears a positive correlation with solar activity when averaged on a shorter time scale, i.e
The electron temperature measured by the SROSS C2 during the period January 1995 to July 2001 has been studied over three latitudes: ±10◦ of the geomagnetic equator and directly over the geomagnetic equator
Summary
Experimental and theoretical study of electron temperature gives insight into the energy balance of the ionosphereplasmasphere regime. Characteristics of electron temperature have been studied using measurements from incoherent scatter radar (McClure, 1969, 1971; Mahajan, 1977; Oliver et al, 1991), rocket probes (Oyama et al, 1980, 1996) and satellite-based instruments (Brace et al, 1967, 1988; Clark et al, 1972; Hanson et al, 1973). The average latitudinal and local time structure of the electron temperature was obtained at the 1000-km altitude from the Explorer 22 satellite (Brace et al, 1967). They showed seasonal dependence of electron density and temperature. They showed seasonal dependence of electron density and temperature. Clark et al (1972) showed the global structure of the electron temperature in the topside ionosphere observed by the ESRO-1A satellite
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