Abstract. During the main and early recovery phase of a geomagnetic storm on February 18, 1998, the Equator-S ion composition instrument (ESIC) observed spectral features which typically represent the di erences in loss along the drift path in the energy range (5±15 keV/e) where the drift changes from being E´B dominated to being gradient and curvature drift dominated. We compare the expected energy spectra modeled using a Volland-Stern electric ®eld and a Weimer electric ®eld, assuming charge exchange along the drift path, with the observed energy spectra for H + and O + . We ®nd that using the Weimer electric ®eld gives much better agreement with the spectral features, and with the observed losses. Neither model, however, accurately predicts the energies of the observed minima.
In this paper, the results of our observations on Al-method ionospheric absorption of radio waves on 1.8 and 2-2 MHz during the solar eclipse of 16 February 1980 are presented. The absorption decreased by about 41% and 46 % of the normal value respectively at the above two frequencies at Ahmedabad following the maximum phase of the eclipse (about 77 ~ of full disc) with a delay of 18 minutes. The quantity At(f) which is a measure of J Nvdh is now examined for better clarity of the influence of the changes in the E-layer. The results are discussed in relation to the observations of the ionizing radiations from the sun, changes in the electron density, recombination rate and absorption in the underlying D and E regions.
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