Evolution of a staircase ion signature observed by Cluster in the polar cusp

P. Escoubet (1) , Jean-Michel Bosqued (2) , J. Berchem (3) , M. G. Taylor (1) , Frederic Pitout (4) , H. Laakso (1) , Arnaud Masson (1) , M.W. Dunlop (5) , H. Reme (2) , I. Dandouras (2) , A. N. Fazakerley (6)

1 ESTEC - European Space Research and Technology Centre
2 CESR - Centre d'étude spatiale des rayonnements
3 IGPP - Institute of Geophysics and Planetary Physics [Los Angeles]
4 MPE - Max-Planck-Institut für Extraterrestrische Physik
5 RAL Space - Space Science and Technology Department [Didcot]
6 MSSL - Mullard Space Science Laboratory

We use the Cluster string of pearl configuration in the mid-altitude polar cusp to investigate temporal variations of the polar cusp. On 7 Aug. 2004, Cluster 4 was moving poleward through the Northern cusp, followed by Cluster 1 about 3 min later, Cluster 2 about 9 min later and finally Cluster 3 about 18 min later. The ACE spacecraft detected a Southward IMF turning before the cusp crossings and Bz stayed negative throughout. Cluster 4 observed a staircase ion dispersion with 2 steps, a high energy one around 1 keV at low latitude and a low energy one at higher latitude. C1 around 3 min later did not observe the high energy step anymore but a dispersion with a low energy cut-off more or less continuous through the cusp. About 18 min later, C3 observed a new dispersion on the equatorward side of the cusp detached from the main cusp precipitation. The observations will be compared with the predictions from a three-dimensional magnetohydrodynamic (MHD) simulation. This event will then be discussed in term of temporal evolution of newly reconnected field lines on the equatorward side of the cusp under IMF-Bz negative.

P. Escoubet, Jean-Michel Bosqued, J. Berchem, M. G. Taylor, Frederic Pitout, et al.. Evolution of a staircase ion signature observed by Cluster in the polar cusp. American Geophysical Union, Fall Meeting 2005, 2005, San Francisco, United States. ⟨insu-00356235⟩