Wave-Particle Interactions in Earth's Inner Magnetosphere: Experimental Results from BARREL

In Earth's inner magnetosphere where the plasmasphere, ring current and radiation belts overlap, energy and momentum are exchanged between different plasma populations by plasma waves. Resonant interaction with these waves can lead to rapid loss of radiation belt and ring current electrons to the atmosphere, called precipitation. For example, electromagnetic ion cyclotron (EMIC) waves are thought to scatter ultra-relativistic electrons into the atmosphere on the duskside of the magnetosphere, while whistler-mode chorus causes rapid (~100ms) electron microbursts near dawn. Over the past six years, more than 50 BARREL (Balloon Array for Radiation Belt Electron Losses) balloons have been launched, making observations of energetic (~20 keV - 10 MeV) electron precipitation in both hemispheres [Millan et al., 2013]. The combination of BARREL multi-point balloon measurements with in situ particle and wave measurements from equatorial spacecraft (e.g. Van Allen Probes, Arase, GOES) provides a unique opportunity to study the wave-particle interactions that cause precipitation. Moreover, BARREL and other low altitude measurements of precipitation (e.g., from POES, CSSWE, FIREBIRD, AC-6) can be used to determine the spatial scale of the region over which the wave-particle interactions occur.