Joule heating associated with auroral electrojets during magnetospheric substorms

Abstract

The magnetospheric substorm is important not only because it involves many interesting physical processes but also because it plays a key role in the solar wind energy dissipation into the ionosphere. This paper focuses on a quantitative description of the Joule heating production rate generated during substorms by auroral electrojets that are composed of two aspects: convection electrojets and the substorm electrojet. First, the natural orthogonal component (NOC) method is carefully discussed by examining its methodology and by comparing with other mathematical techniques and ionospheric observations. It is concluded that the NOC method is a very helpful and unique method that sheds insight into the electric potential patterns in the high-latitude ionosphere. Then, using the AMIE electric potential and the NOC method, the sawtooth event on 18 April 2002 and an isolated substorm on 15 November 2001 are studied. Electric fields and Joule heating rates corresponding to the convection electrojets and the substorm electrojet, respectively, are obtained. It is found that the Joule heating associated with the substorm electrojet is only one fourth to one third of that associated with the convection electrojets during the sawtooth event. However, the former dominated the total Joule heating during the expansion phase of the isolated substorm, and the two types of the Joule heating are comparable in magnitude in the isolated substorm recovery phase. Copyright 2011 by the American Geophysical Union.