Solar Wind Control of Magnetosheath Jet Formation and Propagation to the Magnetopause

Abstract

Magnetosheath jets are localized high‐dynamic pressure pulses originating at Earth's bow shock and propagating earthward through the magnetosheath. Jets can influence magnetospheric dynamics upon impacting the magnetopause; however, many jets dissipate before reaching it. In this study we present a database of 13,096 jets observed by the Time History of Events and Macroscale Interactions during Substorms spacecraft from 2008 to 2018, spanning a solar cycle. Each jet is associated with upstream solar wind conditions from OMNI. We statistically examine how solar wind conditions control the likelihood of jets forming at the shock, and the conditions favorable for jets to propagate through the magnetosheath and reach the magnetopause. We see that, for each solar wind quantity, these two effects are separate, but when combined, we find that jets are over 17 times more likely to reach and potentially impact the magnetopause when the interplanetary magnetic field (IMF) orientation is at a low cone angle, and approximately 8 times more likely during high speed solar wind. Low IMF magnitude, high Alfvén Mach number, and low density approximately double the number of jets at the magnetopause, while β and dynamic pressure display no net effect. Due to the strong dependence on wind speed, we infer that jet impact rates may be solar cycle dependent as well as vary during solar wind transients. This is an important step towards forecasting the magnetospheric effects of magnetosheath jets, as it allows for predictions of jet impact rates based on measurements of the upstream solar wind.

Magnetosheath Jet Occurrence Rate in Relation to CMEs and SIRs

“…A fast SW appears to be somewhat correlated to a higher numbers of jets according to LaMoury et al. ( 2021 ). Specifically, LaMoury et al.…”

“…This could cause the spacecraft to temporarily change the position within the magnetosheath regarding the distance to the bow shock. Because jets are more frequently observed in the close proximity to the bow shock, this plays a role in studying jet statistics (LaMoury et al., 2021 ; Plaschke et al., 2013 ; Vuorinen et al., 2019 ). There are three possible outcomes of this compression regarding the relative position of the spacecraft: First, the spacecraft is positioned within the magnetosheath and the distance to the bow shock shrinks during compression.…”

“…The detection of magnetosheath jets is strongly dependent on the imposed definition and thresholds. Several studies have detected jets by using dynamic pressure thresholds based on the SW (LaMoury et al., 2021 ; Plaschke et al., 2013 ; Vuorinen et al., 2019 ). As we analyze the occurrence of jets during SW disturbances, SW parameters (and subsequently the jet detection thresholds) can rapidly change during these times.…”

“…There have been recent efforts to analyze the general favorable conditions for jet production using statistics of numerous jets (Archer & Horbury, 2013 ; Karlsson et al., 2015 ; LaMoury et al., 2021 ; Plaschke et al., 2013 ). In particular, LaMoury et al.…”

“…In particular, LaMoury et al. ( 2021 ) concluded that favorable conditions for jet formation include low IMF cone angles, both slow and fast SW speeds, low magnetic field strength, high plasma‐ β , low dynamic pressure, high Alfvén Mach number, and low density. They found that jets are more likely to survive the propagation through the magnetosheath with SW conditions showing low IMF cone angle, high SW speed, high IMF magnitude, low plasma‐ β , and high dynamic pressure.…”