Multipoint observations of transient reconnection signatures in the cusp precipitation: A Cluster-IMAGE detailed case study

J. M. Bosqued (1) , C. P. Escoubet , H. U. Frey , M. Dunlop , J. Berchem , A. Marchaudon , J. C. Cerisier , A. Fazakerley , E. Budnik (1) , B. Lavraud (1) , H. Rème (1) , H. Laakso , A. Balogh

1 CESR - Centre d'étude spatiale des rayonnements

, during a period of high solar wind pressure P sw and strongly duskward interplanetary magnetic field (IMF). Simultaneous observations reveal intense cusp activity in the postnoon sector, characterized by multiple, impulsive energy-dispersed ion injections, with a recurrence time of $8-10 min or less. Most of these transient signatures correspond one to one with repeated P sw enhancements. A multipoint analysis reveals that field-aligned current sheets associated with ion steps are moving predominantly westward with a velocity, up to $20 km/s, in agreement with a flux tube motion controlled by magnetic tension forces when IMF B y) 0. These data are used to infer a source region located at $7-13 R E from Cluster, that is, on the dusk flank of the compressed magnetosphere, around 17-18 magnetic local time. We interpret these very dynamic and transient features as probable signatures of pulsed magnetic reconnection that is operating in a localized region of the magnetopause centered in the preferential antiparallel merging site. Our results suggest that the reconnection rate is not spontaneously self-varying but may be directly modulated by either upstream dynamic pressure P sw or changes in the IMF polarity.

Domaines: Astrophysique [astro-ph]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Planète et Univers [physics]

J. M. Bosqued, C. P. Escoubet, H. U. Frey, M. Dunlop, J. Berchem, et al.. Multipoint observations of transient reconnection signatures in the cusp precipitation: A Cluster-IMAGE detailed case study. Journal of Geophysical Research Space Physics, 2005, 110, pp.Issue A3. ⟨10.1029/2004JA010621⟩. ⟨hal-00013058⟩