ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-24-619-2006 Experimental investigation of auroral generator regions with conjugate Cluster and FAST data Marghitu O. 1 2 Hamrin M. 3 Klecker B. 2 Vaivads A. 4 McFadden J. 5 Buchert S. 4 Kistler L. M. 6 Dandouras I. 7 André M. 4 Rème H. 7 Institute for Space Sciences, Bucharest, Romania Max-Planck-Institut für extraterrestrische Physik, Garching, Germany Department of Physics, Umeå University, Umeå, Sweden Swedish Institute of Space Physics, Uppsala, Sweden Space Sciences Lab., University of California at Berkeley, USA Space Science Center, University of New Hampshire, Durham, USA CESR-CNRS, Toulouse, France 23 03 2006 24 2 619 635 Copyright: © 2006 O. Marghitu et al. 2006 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/24/619/2006/angeo-24-619-2006.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/24/619/2006/angeo-24-619-2006.pdf

Here and in the companion paper, Hamrin et al.&nbsp;(2006), we present experimental evidence for the crossing of auroral generator regions, based on conjugate Cluster and FAST data. To our knowledge, this is the first investigation that concentrates on the evaluation of the power density, <i><b>E</b></i>&middot;<i><b>J</b></i>, in auroral generator regions, by using in-situ measurements. The Cluster data we discuss were collected within the Plasma Sheet Boundary Layer (PSBL), during a quiet magnetospheric interval, as judged from the geophysical indices, and several minutes before the onset of a small substorm, as indicated by the FAST data. Even at quiet times, the PSBL is an active location: electric fields are associated with plasma motion, caused by the dynamics of the plasma-sheet/lobe interface, while electrical currents are induced by pressure gradients. In the example we show, these ingredients do indeed sustain the conversion of mechanical energy into electromagnetic energy, as proved by the negative power density, <i><b>E</b></i>&middot;<i><b>J</b></i>&lt;0. The plasma characteristics in the vicinity of the generator regions indicate a complicated 3-D wavy structure of the plasma sheet boundary. Consistent with this structure, we suggest that at least part of the generated electromagnetic energy is carried away by Alfv&#233;n waves, to be dissipated in the ionosphere, near the polar cap boundary. Such a scenario is supported by the FAST data, which show energetic electron precipitation conjugated with the generator regions crossed by Cluster. A careful examination of the conjunction timing contributes to the validation of the generator signatures.