Jets in the magnetosheath: IMF control of where they occur

Laura Vuorinen,Ferdinand Plaschke,Heli Hietala

doi:10.5194/angeo-37-689-2019

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.

Highlights

The varying solar wind and interplanetary magnetic field (IMF) conditions contribute to the dynamic nature of the Earth’s magnetosphere
For the highest IMF cone angle values [60◦, 90◦] when the subsolar magnetosheath is mostly downstream of the quasiperpendicular shock, the distribution is flat but has higher bins around the edges, within the error bars
We can see that the occurrence rates during oblique IMF almost coincide with high cone angle IMF occurrence in the positive end of the Ygipm axis and meets the quasi-radial IMF occurrence rates in the negative end of the Ygipm axis

Summary

Introduction

The varying solar wind and interplanetary magnetic field (IMF) conditions contribute to the dynamic nature of the Earth’s magnetosphere. Some examples of local variations include foreshock transients (e.g., Schwartz and Burgess, 1991), magnetopause surface waves (e.g., Plaschke et al, 2009), and transient structures in the magnetosheath (e.g., Plaschke et al, 2018). A typical size of these jets perpendicular to their flow direction is around 1 RE, and jets larger than 2 RE in diameter can be considered geoeffective (Plaschke et al, 2016). If these jets hit the magnetopause, they can indent the magnetopause, produce magnetopause waves, and trigger phenomena that may affect the inner magnetosphere. It is fair to say that magnetosheath jets play a role in energy transport in the Earth’s magnetosphere

Results

Discussion

Conclusion