Hemispherical Joule heating and the AE indices

A linear regression analysis of Joule energy deposition rates integrated over the northern hemisphere as a function of the standard auroral electrojet indices yields a correlation coefficient of r = 0.7–0.9. Except for very disturbed times, when the AE (12) index tends to underestimate the electrojet current, the hemispherical Joule heating rate can be calculated by substituting 1 nT in the AE index by approximately 0.3 GW. This scale factor is appreciably larger than those employed in earlier energy coupling studies. A higher‐scale factor is found for the regression between Joule heating caused by eastward current versus AU than for that caused by the westward electrojet versus AL . This is consistent with typically lower ionospheric conductivity values in the eastward electrojet region which require higher electric fields and thus more Joule heating for a given eastward current or AU value than for the same intensity of the westward electrojet.