Hot-cold plasma interactions and the generation of transient dayside sub-auroral
proton precipitation

S.A. Fuselier, S P. Gary, M.F. Thomsen, E.S. Claflin, B. Hubert, T.J. Immel,
B.R. Sandel


The IMAGE spacecraft obtained the first global images of the proton aurora. One
of the discoveries from these images was proton precipitation equatorward of the
nominal auroral oval. This precipitation can be observed for approximately 10
minutes immediately following a large solar wind pressure pulse. Various
mechanisms have been proposed for producing this precipitation. Here,
precipitation due to scattering from electromagnetic ion cyclotron (EMIC) waves
is investigated using data from the IMAGE FUV and EUV imagers and in situ data
from the Los Alamos geosynchronous spacecraft. In the proposed EMIC wave
mechanism, the compression of the dayside magnetosphere enhances the growth rate
of the wave instability. These waves scatter hot, ring current protons into the
atmospheric loss cone, reducing the proton temperature anisotropy (the free
energy source of the waves). Two features of the proton precipitation from these
waves require explanation. First, the precipitation pattern may peak at any
local time on the dayside between about 09 and 15. Second, the precipitation
pattern has limited latitudinal extent (typically less than about 10 degrees)
and is often separated from the main auroral oval. The local time peak in the
precipitation pattern is related to the characteristics of the solar wind
pressure pulse that causes EMIC wave growth. The separation of the precipitation
pattern from the main auroral oval is related to properties of the hot and cold
plasma within the magnetosphere that enhance EMIC wave growth.

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Presentation, Fall Meeting, American Geophysical Union, San Francisco, USA, 
8-12 December 2003