Large-scale jets in the magnetosheath and plasma penetration across the magnetopause: THEMIS observations

TL;DR

This study uses THEMIS multi-point observations to analyze large-scale plasma jets in the magnetosheath and their role in plasma penetration across the magnetopause, revealing that nearly 60% of jets penetrate and significantly contribute to magnetospheric plasma entry.

Contribution

It provides the first large-scale statistical analysis of magnetosheath plasma jets and quantifies their impact on plasma transfer into the magnetosphere.

Findings

Almost 60% of jets penetrate the magnetopause.

Penetrating jets have velocities >220 km/s and high kinetic energy.

Estimated plasma entry rate is ~10^29 particles per day.

Abstract

THEMIS multi-point observation of the plasma and magnetic fields, conducted simultaneously in the dayside magnetosheath and magnetosphere, were used to collect 646 large-scale magnetosheath plasma jets interacting with the magnetopause. The jets were identified as dense and fast streams of the magnetosheath plasma whose energy density is higher than that of the upstream solar wind. The jet interaction with the magnetopause was revealed from sudden inward motion of the magnetopause and an enhancement in the geomagnetic field. The penetration was determined as appearance of the magnetosheath plasma against the background of the hot magnetospheric particle population. We found that almost 60% of the jets penetrated through the magnetopause. Vast majority of the penetrating jets was characterized by high velocities V > 220 km/s and kinetic bk > 1 that corresponded to a combination of finite Larmor radius effect with a mechanisms of impulsive penetration. The average plasma flux in the penetrating jets was found to be 1.5 times larger than the average plasma flux of the solar wind. The average rate of jet-related penetration of the magnetosheath plasma into the dayside magnetosphere was estimated to be ~10^29 particles per day. The rate varies highly with time and can achieve values of 1.5*10^29 particles per hour that is comparable with estimates of the total amount of plasma entering the dayside magnetosphere.