Low-latitude and high-latitude geomagnetic agitation

At high latitudes there are statistical morning, afternoon, and night maxima of geomagnetic agitation (irregular disturbance or activity), the complicated distribution and seasonal behavior of which can be explained only in terms of patterned corpuscular bombardment. At subequatorial latitudes there are noon, afternoon, and night maxima, of which only the last two are related to the corresponding high-latitude maxima; the noon maximum, which differs in character from the others, represents a locally generated (Sq) agitation, presumably due to direct solar radiation. Since the afternoon and night maxima are traceable continuously from auroral through middle to low latitudes, and since their respective seasonal variations are everywhere the same, they may be explained as agitation transported from high to low latitudes by an ionospheric current system resembling (and probably identical with) the SD circulation. If so, this circulation is a physical reality, not an analytical construct; the SD currents must flow at their own level, independently of the Dst and Sq circulations. Besides the SD and Sq components of current-transported agitation, there is also a Dst component which, so far as identified, represents pulsative compressions of the geomagnetic field. Sudden commencements have SD, Sq, and Dst components largely analogous to those of agitation.