First simultaneous observation of isolated proton aurora with Pc1 pulsations at subauroral latitudes by an all-sky camera and the Van Allen Probes on 16th March, 2015

Abstract:

Isolated proton auroras (IPAs) are spot-like proton auroras observed simultaneously with Pc1 geomagnetic pulsations at subauroral latitudes. They have been considered to be generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. Thus, the IPA indicates spatial scale and temporal variation of wave-particle interaction region in the magnetosphere. In this study, we report the first simultaneous ground and magnetospheric satellite observations of an IPA using an all-sky imager at Athabasca, Canada, and the Van Allen Probes at ~0532 UT on March 16, 2015. An isolated EMIC wave with a frequency of ~1 Hz was observed by the Van Allen Probes (Probe A) at L~5.0 when the footprint of the satellite crossed over the IPA. This suggests that the IPA was caused by the localized EMIC wave. The proton flux of 5 eV -20 keV increased locally corresponding to the EMIC wave appearance. The temperature anisotropy of the energetic proton was estimated as 1.5-2.5 over a wide L-value range of 3.0-5.2. The electron flux at energies below ~500 eV also increased. The electron density decreased from L=3.5 to L=5.4 with fluctuation. This suggests that the EMIC wave at L~5.0 was occurred near the plasmapause. From these observations, we conclude that the localized IPA and the associated EMIC wave took place due to a localized enhancement of energetic proton flux and a local depletion of plasma density near the plasmapause. The electric and magnetic fields observed by the satellite did not show characteristic DC variations during the wave observation, indicating that the IPA is not accompanied by discernible field-aligned current and plasma flow shear. This is different from the electron aurora in the oval.