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On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm
Author(s) -
Olifer L.,
Mann I. R.,
Ozeke L. G.,
Rae I. J.,
Morley S. K.
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja026348
Subject(s) - geomagnetic storm , storm , geophysics , magnetosheath , diffusion , physics , earth's magnetic field , computational physics , population , electric field , magnetosphere , magnetic field , magnetopause , meteorology , demography , quantum mechanics , sociology , thermodynamics
In this paper, we study electron radial diffusion coefficients derived from Pc4‐Pc5 ultralow frequency (ULF) wave power during the intense geomagnetic storm on 17–18 March 2015. During this storm the population of highly relativistic electrons was depleted within 2 hr of the storm commencement. This radial diffusion, depending upon the availability of source populations, can cause outward radial diffusion of particles and their loss to the magnetosheath, or inward transport and acceleration. Analysis of electromagnetic field measurements from Geostationary Operational Environment Satellite (GOES), Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite, and ground‐based magnetometers shows that the main phase storm‐specific radial diffusion coefficients do not correspond to statistical estimates. Specifically, during the main phase, the electric diffusion ( D L L E ) is reduced, and the magnetic diffusion ( D L L B ) is increased, compared to empirical models based on K p . Contrary to prior results, the main phase magnetic radial diffusion cannot be neglected. The largest discrepancies, and periods of dominance ofD L L BoverD L L E , occur during intervals of strongly southward IMF. However, during storm recovery, both magnetic and electric diffusion rates are consistent with empirical estimates. We further verify observationally, for the first time, an energy coherence for bothD L L BandD L L Ewhere diffusion coefficients do not depend on energy. We show that, at least for this storm, properly characterizing main phase radial diffusion, potentially associated with enhanced ULF wave magnetopause shadowing losses, cannot be done with standard empirical models. Modifications, associated especially with southward IMF, which enhance the effects ofD L L Band introduce larger main phase outward transport losses, are needed.