First Direct Experimental Evidence of Loss Cone Scattering of Energetic Electrons by Plasmaspheric Hiss

Aaron W Breneman1, Dr. Alexa Jean Halford, PhD.2, Robyn M Millan3, John R Wygant4, Cynthia A Cattell4, Leslie A Woodger5, George B Hospodarsky6, Joseph Fennell7, John Glen Sample8, Craig Kletzing9, William S Kurth10, Aleksandr Y Ukhorskiy11, Jerry Goldstein12 and John W Bonnell13, (1)The University of Minnesota, Minneapolis, United States, (2)NASA Goddard Space Flight Center, Greenbelt, United States, (3)Dartmouth College, Department of Physics and Astronomy, Hanover, NH, United States, (4)University of Minnesota Twin Cities, Minneapolis, MN, United States, (5)Dartmouth College, Physics & Astronomy, Hanover, NH, United States, (6)University of Iowa, Physics and Astronomy, Iowa City, IA, United States, (7)Aerospace Corporation Los Angeles, Los Angeles, CA, United States, (8)Montana State University, Bozeman, United States, (9)University of Iowa, Physics and Astronomy, Iowa City, United States, (10)University of Iowa, Iowa City, IA, United States, (11)JHU/APL, Laurel, United States, (12)Southwest Research Institute, San Antonio, United States, (13)University of California Berkeley, Berkeley, CA, United States
Abstract:
A number of physical mechanisms have been identified as potentially important for causing Van Allen radiation belt electron loss. Over 40 years ago it was suggested that loss caused by electron interaction with an electromagnetic plasma wave called plasmaspheric hiss dominates electron loss in the outer portion of the radiation belt that overlaps with a high density region called the plasmasphere. Motivated by the difficulty of observing this loss process with particle detectors on satellites, the Balloon Array for Radiation Belt Relativistic Electron Losses (BARREL) campaign was designed to observe bremsstrahlung x-rays generated by electrons colliding with atmospheric neutrals after removal from the radiation belts. By comparison of x-ray counts to magnetically conjugate plasmaspheric hiss observed on the Van Allen Probes we provide the first direct experimental verification that hiss removes electrons from the radiation belts. X-ray counts and hiss amplitude show similar variation on timescales ranging from minutes to hours. A surprising result is that 1–20 min period fluctuations of x-rays and hiss are coherent on scales comparable to the size of the plasmasphere, far exceeding the few km scale on which wave-particle interactions operate, and establishing that the loss process has global effects on the radiation belts.
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