• K M Kotadia

      Articles written in Proceedings – Section A

    • The great solar flare of february 23, 1956 and associated ionospheric effects at Ahmedabad

      K R Ramanathan R V Bhonsle K M Kotadia R G Rastogi

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    • Variation with lunar phase of midday critical frequencies and heights of the F2 layer over Ahmedabad and other low latitude stations

      K M Kotadia K R Ramanathan

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      The paper contains an analysis of the variation of the midday values of foF2, h′F2 and hpF2 with lunar phase at Ahmedabad during the years 1954 and 1955 and of foF2 alone at Bombay, Madras and Tiruchirapalli during 1954. It is found that while the semidiurnal lunar tidal variations at Ahmedabad and Bombay agree in phase with those observed at middle latitudes, the phase reverses in direction between Bombay and Madras. The results are compared with those relating to Huancayo and Singapore.

    • Erratum

      K R Ramanathan R V Bhonsle K M Kotadia R G Rastogi

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    • The intermediate layer of stratification (F1.5) between F2 and F2 at Ahmedabad

      K M Kotadia

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    • Spread-F in the ionosphere over ahmedabad during the years 1954–57

      K M Kotadia

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      From a study of spread-F or F-scatter at Ahmedabad during the four years 1954–57 of increasing sunspot activity, it was found that the time of its maximum occurrence receded from 03 hr. in low sunspot years to an hour or two before midnight in high sunspot years. This was particularly well seen in the winter and equinoctial months. Also, maximum spread-F activity which was found in summer in sunspot minimum mum years, occurred in equinoxes in maximum sunspot years. The frequency of occurrence of spread-F was found to be a maximum whenhpF2 was in the range 300–350 km. F-scatter and F2-stratification were found to be anti-correlated both in their diurnal and seasonal variations. The general trend was towards decreased spread-F with increased sunspot activity.

      It is concluded that (1) spread-F at Ahmedabad geomagnetic latitude (Φ=13·6° N) undergoes variations similar to those at equatorial stations, more so in high sunspot years, (2) the change-over from low-latitude type to middle-latitude type of variation of spread-F takes place at about geomagnetic latitude 22°, and (3) spread-F at Ahmedabad decreases with increase in magnetic activity, which is the reverse of that observed at high latitudes.

    • Equatorial sporadic E ionization and electrojet effect of geomagnetic disturbances

      K M Kotadia

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      In this paper, the ionospheric data of Kodaikanal (magnetic dip 3·5° N) have been examined to study the relation between the critical frequency of the equatorial sporadic E layer and the horizontal component of the earth’s magnotic field, with special reference to the behaviour of the electrojet both under normal and under disturbed conditions. Some specific SC type magnetic storms have been analysed to study the effect of the storms on the electrojet.

      It is shown that the blanketing frequency of Es can be taken to be equal to the critical frequency of the normal E-layer and it is suggested that the high value of foEs might be due to the subsidence and conversion of E layer ionization into eddy-clouds forming as a result of strong wind shear in the electrojet. It is also shown that foEs and H are fairly well connected undernormal conditions, but the connection is not simple under disturbed conditions. Further, the effect of a magnetic storm in reducing the electrojet current during the main phase is greater in the morning and evening hours; it appears that a depression of about 100 gammas in H-field is necessary before any significant reduction in the electrojet occurs at midday. Finally, some abnormalities in the variations of foEs and H are pointed out.

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