Atmospheric Modulation of the Geomagnetic Daily Variation

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 a t the 10-mb. surface (approximately 30 km.).! The value of a comparative study of the form of the geomapetic 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 geomaghetic and solar data) would be of much help. ,