Continuous magnetic reconnection at Earth's magnetopause

H. U. Frey (1), T. D. Phan (1), S. A. Fuselier (2), S. B. Mende (1)

(1) Space Sciences Laboratory, University of California, Berkeley, California 
    94720-7450, USA
(2) Lockheed Martin Advanced Technology Center, Palo Alto, California 94304, USA


The most important process that allows solar-wind plasma to cross the 
magnetopause and enter Earth's magnetosphere is the merging between solar-wind 
and terrestrial magnetic fields of opposite sense magnetic reconnection. It is 
at present not known whether reconnection can happen in a continuous fashion or 
whether it is always intermittent. Solar flares and magnetospheric substorms - 
two phenomena believed to be initiated by reconnection - are highly burst-like 
occurrences, raising the possibility that the reconnection process is 
intrinsically intermittent, storing and releasing magnetic energy in an 
explosive and uncontrolled manner. Here we show that reconnection at Earth's 
high-latitude magnetopause is driven directly by the solar wind, and can be 
continuous and even quasi-steady over an extended period of time. The dayside 
proton auroral spot in the ionosphere - the remote signature of high-latitude 
magnetopause reconnection -  is present continuously for many hours. We infer 
that reconnection is not intrinsically intermittent; its steadiness depends on 
the way that the process is driven.

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Nature, 426, 533-537, doi:10.1038/nature02084, 2003