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 a significant fraction 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 (THEMIS) spacecraft from 2008–2018, 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 nearly 12 times more likely to
reach and potentially impact the magnetopause when the interplanetary
magnetic field (IMF) is at a low cone angle, and approximately 5 times
more likely during fast solar wind. Low IMF magnitude, high Alfvén Mach
number, and low density approximately double the number of jets at the
magnetopause, while plasma beta 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 space
weather effects of magnetosheath jets, as it allows for predictions of
jet impact rates based on measurements of the upstream solar wind.