News

New Publication: “Quasi-Parallel Shock Reformation Seen by Magnetospheric Multiscale and Ion-Kinetic Simulations” by Andreas Johlander et al.

A shock wave forms when a supersonic flow encounters an obstacle. Shock waves can even form in the ionized plasma that inhabits most of the seemingly empty space in our solar system, galaxy, and the rest of the universe. One such a shock is found in front of Earth as the fast stream of plasma flowing from the Sun, known as the solar wind, encounters Earth’s magnetic field. Under certain conditions, shock waves can become unsteady and evolve in time. Specifically, it is thought that a new shock can form in front of and replace the old shock in a process known as shock reformation. This process is important for how shock waves heat the plasma and can play a major role in how shocks accelerate particles. In this work, we use data from satellites that fly through Earth’s shock and compare to a computer simulation of the shock wave. We find that a type of magnetic pulsation in front of the shock wave causes it to reform. The method of finding this reformation process presented here can also be used in the future to find shock reformation.

Four-spacecraft observation of the shock transition. (a) and (b) Spacecraft positions relative to the tetrahedron center in the GSE xy and xz planes. The shock orientation and shock normal vector before the shock crossing are shown. (c) B observed by the four spacecraft. (d) Reduced ion distribution as a function of vn observed by MMS1.

Full Article:
Johlander, A. (SHARP), Battarbee, M., Turc, L., Ganse, U., Pfau-Kempf, Y., Grandin, M., et al. (2022). Quasi-parallel shock reformation seen by Magnetospheric Multiscale and ion-kinetic simulations. Geophysical Research Letters, 49, doi: 10.1029/2021GL096335


Imaging X-ray Polarimetry Explorer launched successfully

The SHARP collaboration welcomes the successful launch of the NASA SMEX mission Imaging X-ray Polarimetry Explorer (IXPE) on December 9, 2021. The IXPE mission will measure among others the X-ray polarisation from supernova remnants, which helps to probe magnetic-field turbulence in the vicinity of collisionless shocks of these objects. SHARP members Dr. Jacco Vink and Dmitry Prokhorov are scientific members of the IXPE science team and are involved in the analysis of the first science observation done with IXPE, which started on January 10.

Find out more about IXPE here.

Annual Meeting of the APS Division of Plasma Physics

The 63rd Annual Meeting of the APS Division of Plasma Physics was held from Monday to Friday, November 8–12, 2021 in Pittsburgh, PA. During the meeting two sessions of the Mini-Conference on Collisionless Shocks in Laboratory and Space Plasmas were organized (co-conveners: N. Pogorelov, M. Gedalin (SHARP), D. Schaeffer). Most of the topics of the mini-confererence were directly relevant to the research within SHARP.

The talk CM10.00007: Modeling Solar Wind Interaction with the Local Interstellar Medium using Kinetically-Derived Rankine-Hugoniot Conditions for Pickup Ions (N. Pogorelov, M. Gedalin (SHARP), V. S. Roytershteyn, R. K. Bera, F. Fraternale, W. P. Smith, M. Zhang) includes the results obtained by M. Gedalin within the work on Workpackage 2 and 3.
The talk CM10.00006: Kinetic Simulations of the Behavior of Pickup Ions in the Vicinity of a Collisionless Shock (V. S. Roytershteyn, P. F. Kilian, M. Gedalin (SHARP), N. Pogorelov) is also related to the research within the SHARP project.

SHARP involved in new publication on ultralow frequency wave transmission across collisionless shocks

We address the problem of what happens to upstream ultralow frequency (ULF) waves as they reach shocks and are carried into the downstream region. We do this by analyzing the results of 11 2.5D local hybrid simulations of collisionless shocks. We find that the waves are not simply transmitted into the downstream region but that their identity is largely destroyed, as the downstream fluctuations do not resemble the upstream waves neither in wavelengths nor in appearance. However, some features observed in the Fourier spectra of upstream ULF waves are conserved in the Fourier spectra of compressive downstream fluctuations.

Full article:
Kajdič, P., Pfau-Kempf, Y., Turc, L., Dimmock, A. P., Palmroth, M., Takahashi, K., et al. (2021). ULF wave transmission across collisionless shocks: 2.5D local hybrid simulations. Journal of Geophysical Research: Space Physics, 126, doi: 10.1029/2021JA029283

Dmitry Prokhorov and Emanuele Greco joined the SHARP team this autumn

In September, Dmitry Prokhorov started to work on X-ray polarimetry in the group led by Jacco Vink at the University of Amsterdam (UvA). Dmitry will analyze data from the Imaging X-ray Polarimetry Explorer for performing a polarimetric study of supernova remnants to characterize particle acceleration at their shock fronts.

As of October, Emanuele Greco joined UvA as a member of the SHARP team. He will deal with non-thermal emission due to synchrotron radiation in supernova remnants by analyzing observations collected in the X-ray energy band. In particular, he will look for spectral signatures of jittering radiation in young remnants such as Cassiopeia A, Tycho and SN 1006.

New Publication: “Shock Mach Number Estimates Using Incomplete Measurements” by Michael Gedalin et al.

The Mach number is one of the most important parameters of collisionless shocks. The accuracy of its observational determination is compromised by several complications. Incomplete measurements of plasma parameters significantly contribute to the uncertainty, along with the errors of the normal determination. A set of CLUSTER observed shocks is analyzed using several methods for finding the shock normal and to circumvent the shortcomings of the plasma data. A relation between the maximum magnetic compression and the Alfvénic Mach number is established. It is proposed as a proxy for the Mach number estimate when measurements are incomplete.

Theoretical proxy for the Mach number.

Full article:
Gedalin, M., Russell, C. T., Dimmock, A. P. (2021). Shock Mach number estimates using incomplete measurements. Journal of Geophysical Research: Space Physics, 126, doi: 10.1029/2021JA029519