Abstract
Hourly distributions of the angle θXB=arccos (X · B), where X is the solar ecliptic earth‐sun axis and B is the interplanetary magnetic field (IMF), have been compared with hourly Pc 3 and Pc 4 signal activity at Calgary for 198 hours in September, October, and November 1969. Hours whose distributions were concentrated above or below θXB = 50° were correlated with a clear separation of inactive from active micropulsation intervals. The correlation was stronger for the Pc 3 than for the Pc 4 band, and hours with significant fractions, say 10–20% of their θXB distributions below 30°, corresponded particularly well with high amplitudes of micropulsation signals. Signals in the Pc 3 period range on the ground can therefore be used as a crude monitor of certain extremes of IMF orientation.
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