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Title: "Observations of a Global Coherence Scale Modulation of Radiation Belt Electron Loss Resulting from Plasmaspheric Hiss"
Abstract: Over 40 years ago it was suggested that electron loss in the region of the radiation belts that overlaps with the region of high density called the plasmasphere, typically inside radial distances of 4-5 Earth radii is largely due to interaction with an electromagnetic plasma wave called plasmaspheric hiss. Observations to date have found that the long-term electron loss rate is consistent with theory but failed to directly verify temporal and spatial dynamics of the loss process. Here we report on simultaneous measurements of structured radiation belt electron losses and the hiss phenomenon that causes the losses. Losses were observed in the form of bremsstrahlung X-rays generated within Earth's atmosphere by hiss-scattered electrons colliding with atmospheric neutrals after removal from the radiation belts. Our results show that significant (up to order of magnitude) changes in the dynamics of electron loss due to hiss occur on timescales as short as 1-20 min, in association with modulations in density and magnetic field. Furthermore, these loss dynamics are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere, a result that has not been previously observed or predicted in theories of radiation belt electron loss. This brings to the forefront questions about magnetosphere-ionosphere coupling which have not been fully considered. Radiation belt electron loss is often modeled as a continuous drizzle, averaged across large spatial regions. Strong loss modulation and large-scale coherence may significantly impact the loss rate of radiation belt electrons during short-term active periods and lead to modulated ionization in the ionosphere D region.
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