Properties of Dayside Subauroral Proton Flashes Observed with IMAGE-FUV

B. Hubert (Laboratoire de Physique Atmospherique et Planetaire, Universite de
Liege, Belgium), J.-C. Gerard, S.A. Fuselier, S. B. Mende

Recently, a new auroral feature has been identified in response to a solar
wind dynamic pressure pulse buffeting the Earth Magnetosphere. Transient
proton injections are seen to develop on the dayside, detached from the
auroral oval, immediately following the shock arrival. These dayside
subauroral proton flashes are studied using the SI12 Spectrographic Imager of
the IMAGE-FUV experiment. This instrument isolates the Doppler-shifted
Lyman-alpha emission that is solely due to proton aurora. The observed
subauroral proton flashes have a lifetime smaller than 10 minutes, and can
extend to geomagnetic latitudes as low as 60¡. The field lines threading this
region map to the dayside equator at L-shell as low as ~4 Earth radii. The
analysis of the IMAGE-FUV dataset reveals that weak proton flashes can
develop in response to a small solar wind dynamic pressure variation while
bright events take place in relation with major interplanetary shocks.
However, the relation between the flash characteristics and the state of the
magnetosphere prior to the solar wind shock arrival must also be considered.
Indeed, recent theoretical studies have confirmed that the injected protons
are not from solar wind origin, but rather originate from the magnetospheric
reservoir. Possible relations between the morphological characteristics of
the observed dayside subauroral proton flashes and the solar wind properties
will be analyzed. The temporal development of the flash, and in particular
its characteristic lifetime will be estimated, and related to the solar wind
properties and in particular the solar wind dynamic pressure.

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Presentation at the Yosemite Conference of Inner Magnetospheric Interactions,
3 - 6 February 2004, Yosemite, California, USA