Geomagnetic coordinates for the entire Earth

Abstract

During a recent investigation it was found necessary to construct a system of geomagnetic coordinates covering the entire Earth. As these may be found useful to those engaged in terrestrial‐magnetic, cosmic‐ray, and other geophysical researches for finding the geomagnetic coordinates of various places the nomographs prepared are reproduced herewith. Many magnetic phenomena are frequently found to have a relatively simple distribution when consideration is given to the location of the observing stations relative to the pole of the first‐degree harmonics of the Earth's general magnetic field. A coordinate‐system having this pole as its origin is called a system of geomagnetic coordinates . The term magnetic coordinates is sometimes used to denote this system but as magnetic coordinates are sometimes considered as deducible for a point from the magnetic elements at that point the former term avoids ambiguity in considering those based upon the general field. Thus, the magnetic meridian at a point is defined by the declination at that point, the magnetic latitude by the inclination—the tangent of the magnetic latitude being half the tangent of the inclination—while the geomagnetic meridian is the portion of the great circle joining the point to the pole of the first‐degree harmonics and the geomagnetic latitude is the complement of the angular distance along that circle to the pole.