geomagnetic field

The magnetic field in and around the Earth. The intensity of the magnetic field at the Earth’s surface is approximately 32,000 nT at the equator and 62,000 nT at the north pole (the place where a compass needle points vertically downward). The geomagnetic field is dynamic and undergoes continual slow secular changes as well as short-term disturbances (see geomagnetic activity). The geomagnetic field can be approximated by a centered dipole field, with the axis of the dipole inclined to the Earth’s rotational axis by about 11.5 degrees. Geomagnetic dipole north is near geographic coordinate 79 degrees N and 71 degrees W (near Thule, Greenland), and dipole south is near 79 degrees S and 110 degrees E (near Vostok, Antarctica). The observed or dip poles, where the magnetic field is vertical to the Earth’s surface, are near 77 degrees N and 102 degrees W, and 65 degrees S and 139 degrees E. The adopted origin of geomagnetic longitude is the meridian passing through the geomagnetic poles (dipole model) and the geographic south pole. (See also corrected geomagnetic coordinates.)