Filamentary Currents and Alfvénic Vortices in the Inner Magnetosphere

Abstract

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.

Flow Channels and the Generation of Alfvénic Turbulence Along Storm‐Time Inner Magnetospheric Field‐Lines

“…As an example, Figure 1 shows storm‐time measurements from the Van Allen Probes at $$L$$ = 5–6 pre‐midnight near the equatorial plane reported by Chaston et al. (2020). Figures 1a–1g encompass the main phase of the storm and show continuous broadband electromagnetic wave activity (Figures 1a and 1b).…”

The Role of O+ and He+ in the Propagation of Kinetic Alfvén Waves in the Earth’s Inner Magnetosphere

“…It is important to emphasize that in the inner magnetosphere, KAWs have been predominantly observed during geomagnedisturbed time intervals, either during substorms, in association with particle injections from the magnetospheric tail (Wygant et al 2002), or during geomagnetic storms (Chaston et al 2014(Chaston et al , 2015a(Chaston et al , 2015bMoya et al 2015;Chaston et al 2020), over roughly the same period of time in which the abundance of heavy ions increases (Jahn et al 2017). This is consistent with our own findings, which suggest that in the inner magnetosphere, the conditions necessary for the occurrence of KAWs in multispecies plasmas are those that can also be found during geomagnetic storms.…”

Fluid‐Kinetic Variations in the Storm‐Time Inner Magnetosphere

“…The lack of a distinct direction of propagation in the plane perpendicular to $${\boldsymbol{B}}_{\boldsymbol{o}}$$ and the broad distributions of $$\overline{{g}_{i}}\left({k}_{\perp }{\rho }_{i},{\theta }_{k},{\phi }_{k}\,\right)$$ for the Alfvénic mode may be understood by considering the morphology of the fluctuations. Figure 4n shows the “filamentation” of the field variations in the perpendicular plane based on the relationship between the corresponding magnetic field components (Chaston, Bonnell, Wygant, et al., 2020). For planar features consistent with a single plane wave at each $${f}_{SC}$$ and $$t,$$ the value of the filamentation should approach zero.…”