Auroral precipitation and atmospheric vorticity at the 500 mb level

Abstract

On the assumption that, in the long term, auroral and associated particle precipitation is uniform in magnetic time it can be shown that, due to the differing geometries in the northern and southern hemisphere, there exist two regions of maximum particle precipitation in different time zones in U.T. These are the midnight location of the auroral oval between about 1500–1800 h U.T. in the northern hemisphere and between 0000–0600 h U.T. in the southern hemisphere. These times correspond with the maxima of the indices am and am ∗ for the respective winter periods. The northern hemisphere auroral zone precipitation maximum lies above the Siberian winter low pressure region at 500 mb heights which is displaced from the geographic pole. It is suggested that this relative location is basic to the Wilcox boundary crossing-absolute vorticity correlation. The southern hemisphere auroral zone precipitation maximum lies above the Antarctic low pressure region and is near the geographic pole. This results in the lack of a similar correlation as found by Burns.