Depression in the low-latitude horizontal intensity due to quiet-time ring current

Abstract

The external field due to plasma within the magnetosphere has been computed as a function of A_p, which is a measure of solar wind velocity, for very quiet to slightly disturbed conditions using mean daily horizontal intensity from 1932 to 1968 at Alibag. The intensity, corrected for secular change and reduced to a common epoch, showed initially a small increase with A_p followed by a steady depression with further increase in the index. For A_p ~7.5, which is representative of conditions over the 33-hour interval during which data relating to low-energy protons were acquired and used by Hoffman and Bracken [4]²) to compute current distributions, the decrease, computed here from surface data, is 6 γ. This is in goodagreement with the southward directed field of the quiet-time proton belt 9±5 γ obtained by Hoffman and Bracken.