Modeling Kelvin‐Helmholtz Instability at the High‐Latitude Boundary Layer in a Global Magnetosphere Simulation. Issue 19 (7th October 2021)

• Record Type: Journal Article
• Authors: Michael, A. T.; Sorathia, K. A.; Merkin, V. G.; Nykyri, K.; Burkholder, B.; Ma, X.; Ukhorskiy, A. Y.; Garretson, J.
• Is Part Of: Geophysical research letters. Volume 48:Issue 19(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-07
• Subjects: Kelvin‐Helmholtz instability -- geospace modeling -- high‐latitude boundary layer; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL094002
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The Kelvin‐Helmholtz instability at the magnetospheric boundary plays a crucial role in solar wind‐magnetosphere‐ionosphere coupling, particle entry, and energization. The full extent of its impact has remained an open question due, in part, to global models without sufficient resolution to capture waves at higher latitudes. Using global magnetohydrodynamic simulations, we investigate an event when the Magnetospheric Multiscale (MMS) mission observed periodic low‐frequency waves at the dawn‐flank, high‐latitude boundary layer. We show the layer to be unstable, even though the slow solar wind with the draped interplanetary magnetic field is seemingly unfavorable for wave generation. The simulated velocity shear at the boundary is thin ( ∼ 0.65 R E ) and requires commensurately high spatial resolution. These results, together with MMS observations, confirm for the first time in fully three‐dimensional global geometry that KH waves can grow in this region and thus can be an important process for energetic particle acceleration, dynamics, and transport. Plain Language Summary: The boundary separating magnetospheric plasma and the solar wind can become unstable due to the Kelvin‐Helmholtz instability, forming waves that can facilitate mass, momentum, and energy transfer into the magnetosphere. How prevalent Kelvin‐Helmholtz waves are along the magnetopause is therefore a fundamental question to understanding the magnetospheric response to the solar wind. Determining when and where these waves occur on the boundary has remained a challenge. The lower latitudes have been extensively studied while the Cluster mission has provided observations of KH at high‐latitudes. No global models have been capable of resolving the high‐latitude boundary layer, preventing numerical studies of waves within this region. We present a simulation that captures Kelvin‐Helmholtz waves at the high‐latitude boundary for the first time. The instability formed despite the magnetosphere being immersed in pristine slow wind, which reduced the velocity drop across the shear layer at the equator. The simulated period took advantage of an opportunity when the Magnetospheric Multiscale mission was located at the high‐latitude boundary and observed boundary oscillations. Together with the observations, we confirm that Kelvin‐Helmholtz waves can grow at high‐latitudes and thus be able to contribute to particle entry and energization in this region. Key Points: Global magnetohydrodynamic simulation of the magnetosphere captures unstable Kelvin‐Helmholtz waves at the high‐latitude boundary layer for the first time The growth of the surface waves occurs despite the stabilizing slow solar wind and draped magnetic field near the high‐latitude cusp The fastest growing wave mode resolved by the simulation is consistent with Magnetospheric Multiscale mission observations of the same event