Long term ionospheric electron content variations over Delhi

J. K. Gupta, Lakha Singh
2001 Annales Geophysicae  
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
more » ... 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.
doi:10.1007/s005850000296 fatcat:xwqdro4imnbdnm3bww2l3yuo6e