Imprints of impulse-excited hydromagnetic waves on electrons in the Van Allen radiation belts

Author
Keywords
Abstract
Ultralow frequency electromagnetic oscillations, interpreted as standing hydromagnetic waves in the magnetosphere, are a major energy source that accelerates electrons to relativistic energies in the Van Allen radiation belt. Electrons can rapidly gain energy from the waves when they resonate via a process called drift resonance, which is observationally characterized by energy-dependent phase differences between electron flux and electromagnetic oscillations. Such dependence has been recently observed and interpreted as spacecraft identifications of drift resonance electron acceleration. Here we show that in the initial wave cycles, the observed phase relationship differs from that characteristic of well-developed drift resonance. We further examine the differences and find that they are imprints of impulse-excited, coupled fast-Alfv\ en waves before they transform into more typical standing waves. Our identification of such imprints provides a new understanding of how energy couples in the inner magnetosphere, and a new diagnostic for the generation and growth of magnetospheric hydromagnetic pulsations.
Year of Publication
2015
Journal
Geophysical Research Letters
Volume
42
Number of Pages
6199-6204
Date Published
08/2015
URL
http://doi.wiley.com/10.1002/grl.v42.15http://doi.wiley.com/10.1002/2015GL064988
DOI
10.1002/grl.v42.1510.1002/2015GL064988