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SASTRI and MURTHY (1975) examined the magnetograms of Kodaikanal (10014'N, 7728'B in geographic coordinates; +0.6, 147.1 in geomagnetic coordinates; and dip lat. 1.7N), a station in the equatorial electrojet region in India, for the 3-year period 1969-1971, studied the characteristics of 40 welldefined NTSFE events (night-time geomagnetic solar flare effect) and 56 SFE events (day-time geomagnetic solar flare effect) recorded in the Kodaikanal magnetograms, correlated the events with solar and ionospheric data, and concluded that conspicuous geomagnetic effects with sufficient amplitudes in Hcomponent do occur in the dark hemisphere in association with solar X-ray flares observed in the day hemisphere. In Plate 1 of their paper, are shown four typical examples of NTSFE events, which are described as clear-cut, welldefined and large-sized in H -component. These features naturally differ, as pointed out by the authors, from the earlier observations of OHSHIO (1964) who found the NTSFE's to be small in amplitude and not to exhibit a distinct shape even at the maximum stage, based on his study of the events observed at a number of stations in the dark hemisphere. The prominence of NTSFE's at Kodaikanal has been ascribed to the location of Kodaikanal in the equatorial region where relatively strong eastward ionospheric electric currents are supposed to flow at night during solar flares occurring on the sunlit side of the earth. The authors also presented diagrams depicting the results of their analysis of the NTSFE and SFE data for Kodaikanal. Their Fig. 1 shows the occurrence frequency of NTSFE's at Kodaikanal with a peak around the local midnight. Their Fig. 2 shows the most frequent rise-time and total duration of NTSFE as around 35 minutes and 60 minutes respectively, while that of SFE as around 5 minutes and 12 minutes respectively. Their Fig. 3 shows the time correlation of NTSFE events with solar X-ray flares (1-8A) observed on the sunlit side. They also found that the amplitude of the NTSFE is independent of the peak solar X-ray flux level in the two bands 1-8A and 8-20A observed in the day

Discussion on “Geomagnetic Effects in the Dark Hemisphere Associated with Solar Flares”