Abstract
Quiet and disturbed day daily variations ( Sq, Sd) and their difference SD = Sd − Sq are studied for the H component for 1964 for Sverdlovsk, Alibag, Annamalainagar and Trivandrum (all in 60–80°E longitude) after correcting for D st effects which are estimated in two ways; 1. (i) D st ′ obtained as average of Tashkent and Sabhawala near the Sq focus; and 2. (ii) D st ′′ obtained from Sttgitjba and Cain (1970). The results show that (a) Sq is a predominantly day time phenomenon of mostly ionospheric origin, (b) SD is diurnal for mild disturbances and semi-diurnal for large disturbances and consists of a morning increase, a sharp noon decrease giving a reverse current, a recovery to positive current by 20–22 hr LT, followed by a decay to zero level. Implications regarding ionospheric and non-ionospheric contributions are discussed.
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