Multi-point measurements in the cusp: Implications for magnetic reconnection

S. A. Fuselier (1), S. M. Petrinec (1), K. J. Trattner (1), E. S. Claflin (1), 
S. B. Mende (2), H. U. Frey (2), H. R�me (3)

(1) Lockheed Martin Advanced Technology Center
(2) Space Sciences Laboratory, University of California, Berkeley
(3) Centre d.Etude Spatiale des Rayonnements


There is substantial evidence that magnetosheath particles precipitating in 
the cusp cross the magnetopause along open (reconnected) magnetic field lines. 
Considering the low altitude cusp as the confluence of these reconnected field 
lines, it has long been realized that a spacecraft trajectory through the cusp 
or an image of the cusp footpoint provides a global snapshot of reconnection. 
These snapshots provide information on the steadiness of reconnection and the 
conditions under which reconnection occurs at the magnetopause. Recent 
observations from the IMAGE and Cluster spacecraft provide new and unique 
views of the cusp footpoint and the low altitude cusp. IMAGE provides the 
first global images of cusp proton precipitation. The monitoring of the cusp 
footpoint has demonstrated that reconnection is a quasi-steady process
that does not stop even as the interplanetary magnetic field changes 
orientation. Also, these observations show that, at times, reconnection occurs 
between magnetosheath and magnetospheric field lines that are nearly 
anti-parallel. Multi-point measurements in the cusp from the Cluster 
spacecraft confirm that structures seen in cusp ion precipitation are related 
to spatial structures in the cusp and not to temporal variations in the
reconnection rate at the magnetopause. This talk reviews the new IMAGE and 
Cluster results from the cusp.

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Presented at the 34th COSPAR Scientific Assembly, Houston, Texas, U.S.A.  
10-19 October 2002