Changes in the Total Magnetic Energy External to the Earh's Core

The loss of magnetic energy accompanying the decrease in the earth's dipole field during the past 50 years has been shown by McDonald and Gunst to have been balanced by an equal increase in the energy of the nondipole field. It is shown that over time intervals of the order of 2000 years, conservation of the total magnetic energy stored outside the earth's core is not indicated by paleomagnetic measurements of ancient directions and intensities of the field. However during the past 120 years, a decrease in dipole energy at a rate of 5.1×1022ergs/year has been partly balanced by an increase in nondipole energy at a rate of 3.8×1022ergs/year. The net effect is a decrease in the total magnetic energy during the past 120 years at an annual rate of 0.01 percent, which is much less than the average rate during the past 1550 years inferred from paleomagnetic measurements.