Cluster and Double Star multipoint observations of a plasma bubble

• Main Authors: A. P. Walsh, A. N. Fazakerley, A. D. Lahiff, M. Volwerk, A. Grocott, M. W. Dunlop, A. T. Y. Lui, L. M. Kistler, M. Lester, C. Mouikis, Z. Pu, C. Shen, J. Shi, M. G. G. T. Taylor, E. Lucek, T. L. Zhang, I. Dandouras
• Format: Article
• Language: English
• Published: Copernicus Publications 2009-02-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/27/725/2009/angeo-27-725-2009.pdf
• ISSN: 0992-7689; 1432-0576

Depleted flux tubes, or plasma bubbles, are one possible explanation of bursty bulk flows, which are transient high speed flows thought to be responsible for a large proportion of flux transport in the magnetotail. Here we report observations of one such plasma bubble, made by the four Cluster spacecraft and Double Star TC-2 around 14:00 UT on 21 September 2005, during a period of southward, but <I>B_Y</I>-dominated IMF. In particular the first direct observations of return flows around the edges of a plasma bubble, and the first observations of plasma bubble features within 8 <I>R_E</I> of the Earth, consistent with MHD simulations (Birn et al., 2004) are presented. The implications of the presence of a strong <I>B_Y</I> in the IMF and magnetotail on the propagation of the plasma bubble and development of the associated current systems in the magnetotail and ionosphere are discussed. It is suggested that a strong <I>B_Y</I> can rotate the field aligned current systems at the edges of the plasma bubble away from its duskward and dawnward flanks.