We show that broadband low-frequency Alfvénic field variations observed in the inner-magnetosphere from the Van Allen Probes during geomagnetically disturbed intervals are composed of multiscale current sheets, current filaments, flow shears, and vortices. These observations pertain to spacecraft frame frequencies (fsc) over the range 0.1 < fsc < 10 Hz and correspond to structure advected over the spacecraft on scales (λ) over the range 0.1 ≲ λ/ρi ≲ 10. where ρi is the average ion gyroradius. The topology of the current and flow is derived via time domain and spectral approaches adapted for the interpretation of advected structure. The results reveal the action of magnetic and convective nonlinearities in the generation of broadband Alfvénic fluctuations prevalent in the inner magnetosphere during active times. The observed current filamentation and rotational vorticity is suggestive of how broadband Alfvénic field variations on kinetic scales are driven and support geophysically significant particle acceleration in the inner magnetosphere.
Bibliographical noteFunding Information:
This research was supported by the NASA Grants NNX15AF57G, NNX16AG69G, NNX17AD36G, and NNX17AI55G and Van Allen Probes (RBSP) funding provided under NASA prime contract NAS5-01072; including the EFW and EMFISIS investigations under JHU/APL Contract 921647, RBSP-ECT under JHU/APL Contract 967399. Van Allen Probes measurements used in this study can be obtained from the following data repositories: EFW (http://www.space.umn.edu/rbspefw-data/); EMFISIS (http://emfisis.physics.uiowa.edu/data/index; HOPE/MAGEIS/REPT https://www.rbsp-ect.lanl.gov/science/DataDirectories.php); RBSPICE (http://rbspice.ftecs.com/Data.html); and/or by directly contacting the first author.
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- Alfven waves
- geomagnetic stormsVan Allen Probes
- radiation belts
- ring current