Sub-keV Electron Signatures Within Pulsating Aurora

The Rocket Observations of Pulsating Aurora (ROPA) sounding rocket was launched on February 12, 2007 at 12:45:04UT from Poker Flat Research Range, AK into a region of pulsating aurora. Previous measurements of electron precipitation associated with pulsating aurora have varied with many showing high energy, tens to hundreds of keV, modulated populations. ROPA ESA data show sub-keV, downward accelerated structures within a region of widespread, diffuse plasma sheet precipitation, suggesting acceleration by parallel electric fields. These observations are consistent with Sato et al. (2002, 2004) who show FAST measurements of sub-keV inverted-V structures collocated with pulsating aurora. Williams et al. 2006 show observations of modulations of sub-keV electrons in phase with auroral pulsations and concluded that the upgoing secondary electrons created by the high energy precipitation are reflected back downward by a local electric field. In the case of ROPA, the sub-keV electrons appear to have been accelerated through a potential at some altitude above the spacecraft. The resulting secondary electron distribution is altitude dependent, which could help estimate the altitude of the acceleration region using the known distribution of the primary electron precipitation and an estimated potential. Important questions that are addressed include: are the sub-keV electrons measured by the ROPA ESA secondary/backscattered electrons resulting from the primary, plasma sheet precipitation? and at what altitude is the acceleration region associated with these electrons? Do the precipitating particle populations interact with each other in a way, such as two stream instability, that causes the development of double layers and, therefore, parallel electric fields?