ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-26-3375-2008 Observations of vortex-like structure in the cusp-magnetosheath region during northward IMF orientation Tkachenko O. 1 Šafránková J. 1 Němeček Z. 1 Šimůnek J. 2 Přech L. 1 Charles University, Faculty of Mathematics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic Institute of Atmospheric Physics, Czech Academy of Science, Boční 1405, Praha 4, Czech Republic 22 10 2008 26 11 3375 3387 Copyright: © 2008 O. Tkachenko et al. 2008 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/26/3375/2008/angeo-26-3375-2008.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/26/3375/2008/angeo-26-3375-2008.pdf

Two-point observations made by the Interball spacecraft pair unveiled a presence of a large vortex-like structure filled by slow and heated plasma in the outer cusp during periods of the positive <I>B<sub>Z</sub></I> interplanetary magnetic field (IMF) component. We have observed the rotation of the magnetic field and the decrease of its magnitude connected with the presence of a hot plasma population inside the vortex. The structure starts with a clear reversal of the plasma flow caused by reconnection tailward of the cusp that turns a part of the magnetosheath plasma into the cusp. We compare the observations of two spacecraft in detail, discuss the differences between them and suggest the way of a formation such structure. Moreover, the statistical results have confirmed that this phenomenon is probably a regular feature of the high-altitude cusp, however, this relatively small structure cannot be observed too often. The alternative explanation of presented observations as a flapping of the magnetopause is taken into account and discussed.

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