ON PRONOUNCED ATMOSPHERIC MODULATION OF THE GEOMAGNETIC DAILY VARIATION

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Abstract
Seasonal asymmetry in the daily variation of the geomagnetic declination has been studied for the observatories of Honolulu, Hawaii, Tucson, Ariz., and San Juan, Puerto Rico, for an 11-yr. period. Behavior unsymmetrical with respect to the seasonal change of solar radiation is conspicuous and suggests the action of an atmospheric factor, probably the large-scale air circulation in the lower ionosphere. There appears to be a correspondence in time between two evident seasonal changes in the daily variation of the declination and in the large-scale air circulation in the upper stratosphere, as at the 10-mb. surface (approximately 30 km.).1 The value of a comparative study of the form of the geomagnetic daily variation and the daily patterns of large-scale air circulation in the upper stratosphere is emphasized. For studies of this kind it is urged that a greatly condensed daily numerical index of the charts of the upper stratosphere (analogous to the indices that exist for geomagnetic and solar data) would be of much help.

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