Properties of Dayside Subauroral Proton Flashes Observed with IMAGE-FUV

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.