ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Springer Verlag Göttingen, Germany 10.1007/s00585-998-0743-0 Superposed epoch analysis applied to large-amplitude travelling convection vortices Lühr H. 1 Rother M. 1 Iyemori T. 2 Hansen T. L. 3 Lepping R. P. 4 GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany Data Center for Geomagnetism and Space Magnetism, Kyoto University, Kyoto 606-01, Japan Auroral Observatory, University of Tromsø N-9037 Tromsø Norway NASA/Goddard Space Flight Center, Electrodynamics Branch, Greenbelt, MD 20771, USA 31 07 1998 16 7 743 753 Copyright: © 1998 H. Lühr et al. 1998 © European Geosciences Union 1998 This article is available from https://angeo.copernicus.org/articles/16/743/1998/angeo-16-743-1998.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/16/743/1998/angeo-16-743-1998.pdf

For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for large-amplitude travelling convection vortices (TCVs). The restriction to large amplitudes (&gt;100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients 'geoeffective', which have the tendency to recur with the solar rotation period.<br><br><b>Key words. </b>Ionosphere (Aural ionosphere; Ionosphere- magnetosphere interactions) · Magnetospheric Physics (current system)</p>