ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-27-2057-2009 A global study of hot flow anomalies using Cluster multi-spacecraft measurements Facskó G. 1 4 Németh Z. 1 Erdős G. 1 Kis A. 2 Dandouras I. 3 KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary Geodetic and Geophysical Research Institute, Sopron, Hungary CERS, CNRS, Toulouse, France now at: LPCE, CNRS, Orléans, France 05 05 2009 27 5 2057 2076 Copyright: © 2009 G. Facskó et al. 2009 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/27/2057/2009/angeo-27-2057-2009.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/27/2057/2009/angeo-27-2057-2009.pdf

Hot flow anomalies (HFAs) are studied using observations of the magnetometer and the plasma instrument aboard the four Cluster spacecraft. We study several specific features of tangential discontinuities on the basis of Cluster measurements from the time periods of February–April 2003, December 2005–April 2006 and January–April 2007, when the separation distance of spacecraft was large. The previously discovered condition (Facskó et al., 2008) for forming HFAs is confirmed, i.e. that the solar wind speed and fast magnetosonic Mach number values are higher than average. Furthermore, this constraint is independent of the Schwartz et al. (2000)’s condition for HFA formation. The existence of this new condition is confirmed by simultaneous ACE magnetic field and solar wind plasma observations at the L1 point, at 1.4 million km distance from the Earth. The temperature, particle density and pressure parameters observed at the time of HFA formation are also studied and compared to average values of the solar wind plasma. The size of the region affected by the HFA was estimated by using two different methods. We found that the size is mainly influenced by the magnetic shear and the angle between the discontinuity normal and the Sun-Earth direction. The size grows with the shear and (up to a certain point) with the angle as well. After that point it starts decreasing. The results are compared with the outcome of recent hybrid simulations.

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