Martin Ulf Lindberg

and 5 more

Key Points: 8 • The change in electron kinetic entropy per particle is calculated for 22 shock cross-9 ings having wide range of shock conditions 10 • The entropy change displays a strong dependence on the electron beta parame-11 ter 12 • The entropy change corresponds to an adiabatic index γ e = 1.595 ± 0.036 13 Corresponding author: Martin Lindberg, mli6@kth.se-1-Abstract 14 We use Magnetospheric Multiscale (MMS) data to study electron kinetic entropy across 15 Earth’s quasi-perpendicular bow shock. We have selected 22 shock crossings covering a 16 wide range of shock conditions. Measured distribution functions are calibrated and cor-17 rected for spacecraft potential, secondary electron contamination, lack of measurements 18 at the lowest energies and electron density measurements based on the plasma frequency 19 measurements. The change in electron kinetic entropy per particle is calculated for 22 20 shock crossings. 20 out of 22 crossings display an increase in the electron kinetic entropy 21 per particle ranging between 0.1-1.4 k B while two crossings display a slight decrease of 22-0.06 k B. We observe that the change in electron kinetic entropy, ∆S e , displays a strong 23 dependence on the change in electron temperature, ∆T e , and the upstream electron plasma 24 beta, β e. Shocks with high ∆T e are found to have high ∆S e. Shocks with low upstream 25 electron plasma betas are associated to higher ∆S e than shocks with large electron plasma 26 beta. We show that the calculated entropy per particle is strictly less than the maximum 27 state of entropy obtained using a Maxwellian distribution function. The resulting change 28 in electron kinetic entropy per particle ∆S e , density ∆n e and temperature ∆T e is used 29 to determine a value for the adiabatic index of electrons. We find that an adiabatic in-30 dex of γ e = 1.595 ± 0.036 describes the observations best.

Rungployphan Kieokaew

and 27 more

Magnetopause Kelvin-Helmholtz (KH) waves are believed to mediate solar wind plasma transport via small-scale mechanisms. Vortex-induced reconnection (VIR) was predicted in simulations and recently observed using NASA’s Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery of KH waves were also predicted in simulations but detailed observations were still lacking. Here we report MMS observations of an FTE-type structure in a KH wave trailing edge during KH activity on 5 May 2017 on the dawnside flank magnetopause. The structure is characterised by (1) bipolar magnetic BY variation with enhanced core field BZ and (2) enhanced total pressure with dominant magnetic pressure. The cross-section size of the FTE is found to be consistent with vortex-induced flux ropes predicted in the simulations. Unexpectedly, we observe an ion jet (VY), electron parallel heating, ion and electron density enhancements, and other signatures that can be interpreted as a reconnection exhaust at the FTE central current sheet. Moreover, pitch angle distributions of suprathermal electrons on either side of the current sheet show different properties, indicating different magnetic connectivities. This FTE-type structure may thus alternatively be interpreted as two interlaced flux tubes with reconnection at the interface as reported by Kacem et al. (2018) and Øieroset et al. (2019). The structure may be the result of interaction between two flux tubes, likely produced by multiple VIR at the KH wave trailing edge, and constitutes a new class of phenomenon induced by KH waves.

Souhail Dahani

and 15 more

Flux Transfer Events (FTEs) are transient magnetic flux ropes typically found at the Earth’s magnetopause on the dayside. While it is known that FTEs are generated by magnetic reconnection, it remains unclear how the details of magnetic reconnection controls their properties. A recent study showed that the helicity sign of FTEs positively correlates with the east-west (By) component of the Interplanetary Magnetic Field (IMF). With data from the Cluster and Magnetospheric Multiscale missions, we performed a statistical study of 166 quasi force-free FTEs. We focus on their helicity sign and possible association with upstream solar wind conditions and local magnetic reconnection properties. Using both in situ data and magnetic shear modeling, we find that FTEs whose helicity sign corresponds to the IMF By are associated with moderate magnetic shears while those that does not correspond to the IMF By are associated with higher magnetic shears. While uncertainty in IMF propagation to the magnetopause may lead to randomness in the determination of the flux rope core field and helicity, we rather propose that for small IMF By, which corresponds to high shear and low guide field, the Hall pattern of magnetic reconnection determines the FTE core field and helicity sign. In that context we explain how the temporal sequence of multiple X-line formation and the reconnection rate are important in determining the flux rope helicity sign. This work highlights a fundamental connection between kinetic processes at work in magnetic reconnection and the macroscale structure of FTEs.

Katariina Nykyri

and 19 more

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 Magnetosphere Multi-Scale (MMS) mission at the dawn-side high-latitude dayside boundary layer on 25th of February, 2016 between 18:55-20:05 UT. During this interval MMS encountered both inner and outer boundary layer with quasi-periodic 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 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. Wave intervals also showed high energy populations of O+ ions, likely of ionospheric or ring current origin. The counter-streaming electron intervals were associated with a large-magnitude field-aligned Poynting fluxes. Burst mode data at the large Alfven 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 Alfven waves but their contribution to parallel electron heating was not sufficient to explain the > 100 eV electrons, and rapid non-adiabatic heating of the boundary layer as determined by the characteristic heating frequency, derived here for the first time.