IEC and slab thickness near the peak of equatorial anomaly during sunspot maximum and minimum

Abstract

Ionospheric electron content (IEC) measurements for the last solar maximum (1980) using Faraday rotation technique at Rajkot (lat., 22.3°N; long., 70.7°E; subionospheric dip lat., 16.5°N) are reported. The diurnal variation shows tendency for post-sunset enhancements in IEC during equinox and winter. The winter daytime IEC values are <img src='/image/spc_char/wave.gif' border=0> 29% higher than the summer values indicating seasonal anomaly. Results are compared with earlier measurements during low sunspot year (1975). Contours of IEC and equivalent slab thickness (<img src='/image/spc_char/tow.gif' border=0>) are presented. Electrojet control of the daytime peak IEC and lack of dependence of IEC on magnetic activity at least for moderate magnetic disturbances are pointed out. The results are discussed in terms of the effect of EXB drift on diurnal variation, particularly for high sunspot year. The role of composition changes in seasonal changes of IEC and <img src='/image/spc_char/tow.gif' border=0> and conjugate point plasma transfer and H⁺ <img src='http://www.niscair.res.in/jinfo/rightarrow.gif' border=0> O⁺ transition levels in producing pre-sunrise peaks of <img src='/image/spc_char/tow.gif' border=0> are presented.