The geomagnetic field in space, ring currents, and auroral isochasms

Abstract

Using a 48-coefficient spherical harmonic expansion of the geomagnetic field for 1955.0, the results of an analysis due to Finch and Leaton, it is shown that geomagnetic field lines appear to interlink the northern and southern auroral zones. Theoretical average auroral isochasms are also estimated using an integral invariant for particle motion along the lines of force and between the northern and southern hemispheres. Some conditions pertinent to simultaneity and similarity of the aurora borealis and the aurora australis are discussed. Though the auroral zones northern and southern shift in latitude with time, in accord with the intensity of magnetic disturbances, the average auroral zone remains a useful parameter in polar studies. The geographical distribution of isochasms appears to be successfully calculated from the geomagnetic field alone and an integral invariant of particle motion. The intersections of particular geomagnetic field lines with the earth's surface in the northern and southern hemispheres, or conjugate points, are indicated.