Substructure of a Kelvin‐Helmholtz Vortex Accompanied by Plasma Transport Under the Northward Interplanetary Magnetic Field

• Published in: Journal of geophysical research. Space physics Vol. 127; no. 2
• Main Authors: Yan, G. Q., Mozer, F. S., Parks, G. K., Cai, C. L., Chen, T., Goldstein, M. L., Ren, Y.
• Format: Journal Article
• Language: English
• Published: 01-02-2022
• Subjects: electrostatic field; Kelvin‐Helmholtz Vortex; plasma transport; Rayleigh‐Taylor instablity; secondary process; substructure
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2021JA029735

Within a Kelvin‐Helmholtz (K‐H) vortex at the duskside magnetopause, a substructure characterized by two flux enhancements of cold magnetosheath plasma in a background of hot magnetosphere plasma is observed. The substructure is accompanied by plasma transport across the magnetopause, and the transport region is found to split into two parts: the double peaks in both ion and electron densities, corresponding to the two flux enhancements in spectrograms. There are two decreases in the ion temperature while the electron temperature remains constantly low, suggesting that the substructure is caused by a secondary process within the vortex rather than the secondary crossings of the vortex or the boundary oscillations. A transverse motion of cold plasma is observed in the pitch‐angle distribution, demonstrating an example of transverse driving and ongoing plasma transport across the magnetopause. With the convective electric field removed, the perturbed electric field E1, which is sinusoidal and perpendicular to B, matches the theoretical prediction of the Rayleigh‐Taylor (R‐T) instability. Such a perturbed electric field is expected to be the electrostatic field that accompanies the R‐T instability producing the substructure and drives the plasma transport by E1×B ${\boldsymbol{E}}_{1}\times \boldsymbol{B}$ drift. The observations suggest that this secondary R‐T instability within the K‐H vortex can drive plasma transport across the magnetopause.
Plain Language Summary
The Earth's intrinsic magnetic field creates a bubble called the magnetosphere which protects the planet from direct bombardment by the solar wind. The outer edge of the magnetosphere, the magnetopause, prevents the direct incursion of solar wind plasma into the magnetosphere. Sometimes, the solar wind can penetrate into the magnetosphere by changing the topology of the magnetopause via a process known as magnetic reconnection. In addition, transport can proceed via the Kelvin‐Helmholtz (K‐H) instability which creates vortices, the ripples on the flanks of the magnetopause, as shown in some numerical simulations (Matsumoto & Hoshino, 2004, 2006; https://doi.org/10.1029/2003gl018195, https://doi.org/10.1029/2004ja010988). Here, based on spacecraft observations thousands of miles away, we show a secondary structure of the plasma transport across the magnetopause within a K‐H vortex. The observations of both plasma and electric fields have revealed detailed microphysics of plasma transfer within the ripples at the magnetopause.
Key Points
A substructure of a parent K‐H vortex is identified in THEMIS observations at the duskside magnetopause
The perturbed electric field, which accompanies the formation of the substructure by the secondary R‐T instability, is detected
Transverse motion of cold plasmas is observed in the substructure, indicating the occurrence of the plasma transport driven by E1×B ${\boldsymbol{E}}_{1}\times \boldsymbol{B}$ drift