Annales Geophysicae www.ann-geophys.net 0992-7689 1432-0576 22 12 2004 10.5194/angeo-22-4133-2004 http://www.ann-geophys.net/22/4133/2004/ http://www.ann-geophys.net/22/4133/2004/angeo-22-4133-2004.html http://www.ann-geophys.net/22/4133/2004/angeo-22-4133-2004.pdf 4133 4142 2004-12-22 Statistics of Joule heating in the auroral zone and polar cap using Astrid-2 satellite Poynting flux A. Olsson P. Janhunen T. Karlsson N. Ivchenko L. G. Blomberg Swedish Institute of Space Physics, Uppsala, Sweden Finnish Meteorological Institute, Space Research, Helsinki, Finland Alfvén Laboratory, Royal Institute of Techology, Stockholm, Sweden We make a statistical study of ionospheric Joule heating with the Poynting flux method using six months of Astrid-2/EMMA electric and magnetic field data during 1999 (solar maximum year). For the background magnetic field we use the IGRF model. Our results are in agreement with earlier statistical satellite studies using both the Σ<i>_PE</i>² method and the Poynting flux method. We present a rather comprehensive set of fitted Joule heating formulas expressing the Joule heating in given magnetic local time (MLT) and invariant latitude (ILAT) range under given solar illumination conditions as a function of the <i>K_p</i> index, the <i>AE</i> index, the Akasofu epsilon parameter and the solar wind kinetic energy flux. The study thus provides improved and more detailed estimates of the statistical Joule heating. Such estimates are necessary building blocks for future quantitative studies of the power budget in the magnetosphere and in the nightside auroral region.<br><br> <b>Key words.</b> Ionosphere (electric fields and currents; ionosphere-magnetosphere interactions) – Magnetospheric physics (magnetospheric configuration and dynamics)