Spatial coherence of geomagnetic rapid variations

The auto and cross spectrums of geomagnetic total intensity time variations were studied for four systematically arranged pairs of stations. The stations were in the northeastern United States and were separated by distances of up to 550 km in the north-south and east-west directions. At each station the field intensity was digitized once each second to an accuracy of ±0.02 gamma. Approximately 88 hours of such synoptic recording were used in this study. The spectrum results were found to be stable when processed in hourly batches. The variations contain two component parts: The rapid variation background (or agitation) component appears to be due to turbulence in the Sq current system since spectrum amplitude is related to the strength of the Sq; cross-station coherence is high and relative phase undergoes a change of sign at the edges of the Sq current systems. The second component is the relatively narrow-band micropulsation component. The micropulsations have measurable phase differences between stations. When two or more pulsation bands occur simultaneously, they are independent of one another and of the background. Independent excitation mechanisms must exist for these types of rapid variation activity.