More Like this

1. Magnetohydrodynamic Turbulence in the Earth’s Magnetotail From Observations and Global MHD Simulations

   https://doi.org/10.3389/fspas.2021.620519  

   El-Alaoui, Mostafa ; Walker, Raymond J. ; Weygand, James M. ; Lapenta, Giovanni ; Goldstein, Melvyn L. ( March 2021 , Frontiers in Astronomy and Space Sciences)

   null (Ed.)

   Magnetohydrodynamic (MHD) turbulent flows are found in the solar wind, the magnetosheath and the magnetotail plasma sheet. In this paper, we review both observational and theoretical evidence for turbulent flow in the magnetotail. MHD simulations of the global magnetosphere for southward interplanetary magnetic field (IMF) exhibit nested vortices in the earthward outflow from magnetic reconnection that are consistent with turbulence. Similar simulations for northward IMF also exhibit enhanced vorticity consistent with turbulence. These result from Kelvin-Helmholtz (KH) instabilities. However, the turbulent flows association with reconnection fill much of the magnetotail while the turbulent flows associated with the KH instability are limited to a smaller region near the magnetopause. Analyzing turbulent flows in the magnetotail is difficult because of the limited extent of the tail and because the flows there are usually sub-magnetosonic. Observational analysis of turbulent flows in the magnetotail usually assume that the Taylor frozen-in-flow hypothesis is valid and compare power spectral density vs. frequency with spectral indices derived for fluid turbulence by Kolmogorov in 1941. Global simulations carried out for actual magnetospheric substorms in the tail enable the results of the simulations to be compared directly with observed power spectra. The agreement between the two techniques provides confidence that the plasma sheet plasma is actually turbulent. The MHD results also allow us to calculate the power vs. wave number; results that also support the idea that the tail is turbulent. 

   more » « less
2. Ion Dynamics in the Meso-scale 3-D Kelvin–Helmholtz Instability: Perspectives From Test Particle Simulations

   https://doi.org/10.3389/fspas.2021.758442  

   Ma, Xuanye ; Delamere, Peter ; Nykyri, Katariina ; Burkholder, Brandon ; Eriksson, Stefan ; Liou, Yu-Lun ( November 2021 , Frontiers in Astronomy and Space Sciences)

   Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the cross-scale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different test particle approaches and cross validates the different results against one another to investigate the behavior of different ion species (i.e., H+ and O+), which include particle distributions, mixing and heating. It shows that the ion transport rate is about 10 25  particles/s, and mixing diffusion coefficient is about 10 10  m 2  s −1 regardless of the ion species. Magnetic field lines change their topology via the magnetic reconnection process driven by the three-dimensional KH instability, connecting two flux tubes with different temperature, which eventually causes anisotropic temperature in the newly reconnected flux. 

   more » « less
3. Characteristics of Kelvin–Helmholtz Waves as Observed by the MMS From September 2015 to March 2020

   https://doi.org/10.1029/2021JA029685  

   Rice, Rachel C. ; Nykyri, Katariina ; Ma, Xuanye ; Burkholder, Brandon L. ( March 2022 , Journal of Geophysical Research: Space Physics)

   The Magnetospheric Multiscale (MMS) mission has presented a new opportunity to study the fine scale structures and phenomena of the Earth’s magnetosphere, including cross scale processes associated with the Kelvin–Helmholtz Instability (KHI), but such studies of the KHI and its secondary processes will require a database of MMS encounters with Kelvin–Helmholtz (KH) waves. Here, we present an overview of 45 MMS observations of the KHI from September 2015 to March 2020. Growth rates and unstable solid angles for each of the 45 events were calculated using a new technique to automatically detect plasma regions on either side of the magnetopause boundary. There was no apparent correlation between solar wind conditions during the KHI and its growth rate and unstable solid angle, which is not surprising as KH waves were observed downstream of their source region. We note all KHI were observed for solar wind flow speeds between 295 and 610 km/s, possibly due to a filtering effect of the instability onset criteria and plasma compressibility. Two‐dimensional Magnetohydrodynamic (2D MHD) simulations were compared with two of the observed MMS events. Comparison of the observations with the 2D MHD simulations indicates that the new region sorting method is reliable and robust. The ability to automatically detect separate plasma regions on either side of a moving boundary and determine the KHI growth rate may prove useful for future work identifying and studying secondary processes associated with the KHI.

    

   more » « less
4. MMS Observations of the Multiscale Wave Structures and Parallel Electron Heating in the Vicinity of the Southern Exterior Cusp

   https://doi.org/10.1029/2019JA027698  

   Nykyri, K. ; Ma, X. ; Burkholder, B. ; Rice, R. ; Johnson, J. R. ; Kim, E‐K. ; Delamere, P. ; Michael, A. ; Sorathia, K. ; Lin, D. ; et al ( March 2021 , Journal of Geophysical Research: Space Physics)

   Understanding the physical mechanisms responsible for the cross‐scale energy transport and plasma heating from solar wind into the Earth's magnetosphere is of fundamental importance for magnetospheric physics and for understanding these processes in other places in the universe with comparable plasma parameter ranges. This paper presents observations from the Magnetosphere Multiscale (MMS) mission at the dawn‐side high‐latitude dayside boundary layer on February 25, 2016 between 18:55 and 20:05 UT. During this interval, MMS encountered both the inner and outer boundary layers with quasiperiodic low frequency fluctuations in all plasma and field parameters. The frequency analysis and growth rate calculations are consistent with the Kelvin‐Helmholtz instability (KHI). The intervals within the low frequency wave structures contained several counter‐streaming, low‐ (0–200 eV) and mid‐energy (200 eV–2 keV) electrons in the loss cone and trapped energetic (70–600 keV) electrons in alternate intervals. The counter‐streaming electron intervals were associated with large‐magnitude field‐aligned Poynting fluxes. Burst mode data at the large Alfvén velocity gradient revealed a strong correlation between counter streaming electrons, enhanced parallel electron temperatures, strong anti‐field aligned wave Poynting fluxes, and wave activity from sub‐proton cyclotron frequencies extending to electron cyclotron frequency. Waves were identified as Kinetic Alfvén waves but their contribution to parallel electron heating was not sufficient to explain the >100 eV electrons.

    

   more » « less
5. Diffusive Plasma Transport by the Magnetopause Kelvin-Helmholtz Instability During Southward IMF

   https://doi.org/10.3389/fspas.2021.809045  

   Nakamura, T. K. ; Blasl, K. A. ; Liu, Y. -H. ; Peery, S. A. ( January 2022 , Frontiers in Astronomy and Space Sciences)

   At the Earth’s low-latitude magnetopause, the Kelvin-Helmholtz (KH) waves, which are driven by the super-Alfvénic velocity shear across the magnetopause, have been frequently observed during periods of northward interplanetary-magnetic-field (IMF) and believed to contribute to efficiently transporting the solar wind plasmas into the magnetosphere. On the other hand, during southward IMF periods, the signatures of the KH waves are much less frequently observed and how the KH waves contribute to the solar wind transport has not been well explored. Recently, the Magnetospheric Multiscale (MMS) mission successfully detected signatures of the KH waves near the dusk-flank of the magnetopause during southward IMF. In this study, we analyzed a series of two- and three-dimensional fully kinetic simulations modeling this MMS event. The results show that a turbulent evolution of the lower-hybrid drift instability (LHDI) near the low-density (magnetospheric) side of the edge layer of the KH waves rapidly disturbs the structure of the layer and causes an effective transport of plasmas across the layer. The obtained transport rate is comparable to or even larger than that predicted for the northward IMF. These results indicate that the diffusive solar wind transport induced by the KH waves may be active at the flank-to-tail magnetopause during southward IMF. 

   more » « less