Jets in the magnetosheath: IMF control of where they occur

Abstract

Abstract. Magnetosheath jets are localized regions of plasma that move faster towards the Earth than the surrounding magnetosheath plasma. Due to their high velocities, they can cause indentations when colliding into the magnetopause and trigger processes such as magnetic reconnection and magnetopause surface waves. We statistically study the occurrence of these jets in the subsolar magnetosheath using measurements from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and OMNI solar wind data from 2008 to 2011. We present the observations in the BIMF–vSW plane and study the spatial distribution of jets during different interplanetary magnetic field (IMF) orientations. Jets occur downstream of the quasi-parallel bow shock approximately 9 times as often as downstream of the quasi-perpendicular shock, suggesting that foreshock processes are responsible for most jets. For an oblique IMF, with 30–60∘ cone angle, the occurrence increases monotonically from the quasi-perpendicular side to the quasi-parallel side. This study offers predictability for the numbers, locations, and magnetopause impact rates of jets observed during different IMF orientations, allowing us to better forecast the formation of these jets and their impact on the magnetosphere.

Classifying Magnetosheath Jets using MMS - Statistical Properties

“…The results of our study show that quasi-parallel jets are considerably more frequent than quasi-perpendicular jets. Specifically, similar to recent results (Vuorinen et al, 2019), they were found to occur ∼ 5−10 times more frequently than quasi-perpendicular jets. On average they have a dynamic pressure around 3.5 nPa, with the majority of them exhibiting both a density and a velocity increase.…”

“…Furthermore, jets can generate a vortical motion in the background magnetosheath plasma, causing a deceleration to the ambient plasma around the jet . It has been recently shown that jets occur roughly 9 times more often downstream of the quasi-parallel bow shock compared to the quasi-perpendicular one (Vuorinen et al, 2019). This is in agreement with the observations showing low solar wind cone angles favoring the creation of subsolar magnetosheath jets, while other solar wind parameter variations have no significant effect (Plaschke et al, 2013).…”

Classifying Magnetosheath Jets Using MMS: Statistical Properties

“…Furthermore, jets can generate a vortical motion in the background magnetosheath plasma, causing a deceleration to the ambient plasma around the jet (Plaschke & Hietala, 2018). It has been recently shown that jets occur roughly 9 times more often downstream of the quasi‐parallel bow shock compared to the quasi‐perpendicular one (Vuorinen et al, 2019). This is in agreement with the observations showing low solar wind cone angles favoring the formation of subsolar magnetosheath jets, while other solar wind parameter variations have no significant effect (Plaschke et al, 2013).…”

Statistical Study of Magnetosheath Jet‐Driven Bow Waves

“…Such magnetosheath jets are characterized by very large dynamic pressure that are comparable to that of the solar wind. Magnetosheath jets are more likely to occur downstream of the quasi-parallel rather than the quasi-perpendicular bow shock (e.g., Plaschke et al, 2013;Vuorinen et al, 2019). One possible reason is that the surface of the quasi-parallel bow shock is rippled (e.g., Gingell et al, 2017;Hao et al, 2017;Karimabadi et al, 2014).…”