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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 6
Ann. Geophys., 13, 633–640, 1995
https://doi.org/10.1007/s00585-995-0633-7
© European Geosciences Union 1995
Ann. Geophys., 13, 633–640, 1995
https://doi.org/10.1007/s00585-995-0633-7
© European Geosciences Union 1995

  30 Jun 1995

30 Jun 1995

Solar cycle and seasonal variations in F-region vertical drifts over Kodaikanal, India

K. B. Ramesh and J. H. Sastri K. B. Ramesh and J. H. Sastri

Abstract. Measurements of the changes in phase path of F-region reflections at normal incidence at Kodaikanal (77° 28'E, 10° 14'N, dip 3°N) from February 1991 to February 1993 are used to determine the variation of the equatorial evening F-region vertical drifts (V z) with season, solar and magnetic activity. It is found that on average, at Kodaikanal, the post-sunset peak in Vz(Vzp) is higher in equinox and local winter months than in local summer. The day-to-day variability in V zp is highest in summer and lowest in winter. This seasonal trend persists even on magnetically quiet days (Ap \leq14). Vzp is found to increase with 10.7 cm solar flux in all three seasons but tends to saturate for large flux values (>230 units) during local summer and winter months. Magnetic activity [represented by Ap as well as the time-weighted accumulations of a p and ap (τ)] does not seem to have any statistically significant effect on Vzp , except during equinoctial months of moderate solar activity, when Vzp decreases as magnetic activity increases.

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