High resolution simulations of the inner heliosphere in search of the Kelvin-Helmholtz waves

Abstract:

The solar wind consists of streams with different velocities, and the boundary layers between the streams can potentially lead to the generation of the Kelvin-Helmholtz (KH) instability. We use the Grid Agnostic MHD for Extended Research Applications (GAMERA) MHD model driven by the Wang-Sheeley-Arge (WSA) model of the corona (which was, in turn, driven by photospheric magnetograms) to simulate the Carrington rotation 2210 corresponding to the first Parker solar probe (PSP) perihelion at unprecedented resolution. We compare the GAMERA simulation results with the PSP observations. The simulation is the highest resolution of the global MHD models available to us today and can resolve the heliospheric plasma and magnetic structure to within 0.2 solar radius (150,000 km). We demonstrate the radial velocity shears as well as intense off-radial velocity shears to study the stability of the KH instability in the inner heliosphere with our simulation. Radial shears are stabilized by the compressibility and off-radial shears have a narrow window, depending on the Alfven speed and sound speed, for the KH instability to grow until the interplanetary magnetic field turns azimuthal to stabilize the fastest growing mode. The current resolution has barely entered the inertial range of the solar wind turbulence. Simulations at even higher resolution would extend well into the inertial range, and we suggest that they can be leveraged either to finally demonstrate the in situ generation of KH instability in the solar wind or, on the contrary, to refute the hypothesis of its existence. Such a simulation would bridge the gap between state-of-the-art turbulence simulations in limited domains and global inner heliosphere simulations.