Statistical Differences of Magnetic Field Kinks Observed by PSP and WIND

<p>Parker Solar Probe’s (PSP) observations near the sun show the extensive presence of magnetic field kinks (switchback for large kinks) in the slow solar wind. These kinks are usually accompanied by the enhancement of radial solar wind velocity and ion temperature, increasing or decreasing of number density. The magnetic field kinks have also been observed by WIND and Ulysses to exist near and beyond 1 AU, respectively. In this study, we statistically analyze the property difference of magnetic field kinks observed by PSP and WIND. We obtain the following four points of results. (1) Inside the PSP-kinks, the radial velocity and protons’ temperature increase while density shows enhancement or descent. However, inside the WIND-kinks, besides the slight enhancement of radial velocity, the density and temperature show no obvious change compared with the outside plasma. (2) By employing the Walen-test of kinks, we find that, R components of some PSP-kinks but not all satisfy the rotational discontinuity (RD) features, while the three components of most WIND-kinks well match the RD features. (3) The correlation between magnetic field and velocity inside the PSP-kinks and WIND-kinks does not show significant differences. (4) Both the PSP-kinks and WIND-kinks can be divided into two groups based on the histograms of θ<sub>Bn</sub>, where B is the background magnetic field, and n is the normal direction of kink. The first group (group-I) has θ<sub>Bn</sub> concentrating around 20° for PSP-kinks and 30° for WIND-kinks, indicating that the satellites were crossing the same kinked interplanetary magnetic field (IMF) from the upstream to the downstream. The second group (group-II) has θ<sub>Bn</sub> concentrating around 90° for PSP-kinks and WIND-kinks, suggesting that the satellites were crossing an interface between the unkinked and kinked IMF regions. Our findings help better understanding the nature of kinks and provide the observational basis for testifying models about radial propagation and evolution of magnetic field kinks.</p>

Properties of the whistler precursor upstream of the foreshock bubble shock: MMS observations

<p>Foreshock bubbles (FBs) are kinetic phenomena that can form when a rotational discontinuity or a tangential discontinuity interacts with backstreaming ions in the Earth’s foreshock region. The scale of FBs can be up to 10 R<sub>E</sub> and the expansion speeds can be more than 100 km/s. The expansion of the hot ions contributes to the formation of a new shock on the trailing edge of an FB. Using MMS data, we analyze properties of the FB shock and the whistler precursor upstream of it. For the twelve FBs we analyzed, the FB shock normal has a strong X component in GSE coordinates and the quasi-parallel FB shocks are in favor of the generation of the whistler precursor. When the Mach number is larger than 3.5, the whistler precursor disappears. The wave forms are not phase standing since the angle of the wave vector and shock normal is larger than 9 degrees. They have frequencies near <em>f<sub>LH </sub></em>and right-hand polarization with respect to the ambient magnetic field (in the spacecraft frame). The properties of the whistler precursor upstream of the FB shock are similar to those at interplanetary shocks.</p>

Energy conversion by electron beam-driven waves in a compressed reconnection separatrix

<p>We investigate magnetic compression near the reconnection separatrix observed by Magnetospheric MultiScale (MMS) on July 11<sup>th</sup> 2017. A clear transition between inflow and outflow in both ions and electrons is observed across an ion gyro-scale region of enhanced magnetic field. Multispacecraft techniques for magnetic curvature and local gradients along with timing of highly-correlated wave packets are used to determine the spatial configuration of the compressed region. Structure of the system is found to be inherently three dimensional; electron beam-driven modes propagating parallel to the magnetic field are observed concurrent with perpendicular-propagating lower hybrid waves. Larger scale surface waves are also present behind the compression front. Transforming to a deHoffmann-Teller frame across the boundary results in a distinctly non-rotational discontinuity with structure similar to a quasi-2D, Petschek-like slow shock. However, MHD jump conditions are not satisfied, indicating kinetic dissipation may occur within the thin layer. The largest amplitude measurements of $\mathbf{J}\cdot\mathbf{E}$ energy conversion are associated with an inflowing electron beam and parallel electric fields near the magnetic peak. Spikes in $\mathbf{J}\cdot\mathbf{E}$ are predominantly negative, suggesting electron-scale mixing between the reconnection inflow and outflow is partially responsible for the observed magnetic compression.</p>