Observation of dayside subauroral proton flashes with IMAGE-FUV.

The IMAGE-FUV experiment onboard the IMAGE satellite includes three imagers: the WIC and SI13 instruments produce a global scale imaging of the N_2 LBH wavelength range and of the OI 130.4 nm emission respectively, and are thus devoted to the study of the electron aurora. The third imager, SI12, remotely senses the Doppler shifted Lyman-alpha emission, that is solely due to the proton aurora, at the global scale. We present here a new auroral feature observed with the SI12 instrument, consisting of sudden dayside subauroral injections of protons at magnetic latitudes sometimes lower than 60^o MLAT, at the foot of field lines of L shells as low as 4 RE. The extension of the feature in magnetic local time is variable and cases extending from Ë 0700 to Ë 1500 MLT were seen. The relaxation time of these features will be discussed. Most of these dayside subauroral proton flashes are found to be related to sudden solar wind dynamic pressure pulses, but a few counter examples were found. The relationship with the IMF orientation is investigated.