Magnetosheath Jet Formation Influenced by Parameters in Solar Wind Structures

Magnetosheath jets are dynamic pressure enhancements observed in the terrestrial magnetosheath. Their generation mechanisms are currently debated but the majority of jets can be linked to foreshock processes. Recent results showed that jets are less numerous when coronal mass ejections (CMEs) cross the magnetosheath and more numerous when stream interaction regions (SIRs) cross it. Here, we show for the first time how the pronounced substructures of CMEs and SIRs are related to jet production. We distinguish between compression and magnetic ejecta (ME) regions for the CME as well as compression region associated with the stream interface and high-speed streams (HSSs) for the SIR. Based on THEMIS and OMNI data covering 2008–2021, we show the 2D probability distribution of jet occurrence using the cone angle and Alfvén Mach number. We compare this distribution with the values within each solar wind (SW) structure. We find that both high cone angles and low Alfvén Mach numbers within CME-MEs are unfavorable for jet production as they may inhibit a well-defined foreshock region. 1D histograms of all parameters show, which SW parameters govern jet occurrence in each SW structure. In terms of the considered parameters the most favorable conditions for jet generation are found for HSSs due to their associated low cone angles, low densities, and low magnetic field strengths.

Key Points
We show how plasma parameters in solar wind structures are related with jet occurrence
High cone angles and low Alfvén Mach numbers associated with the magnetic ejecta of coronal mass ejections presumably reduce the generation of jets
We found that plasma parameters in high-speed streams represent the most favorable physical condition for jet generation

Plain Language Summary
The Sun produces a constant outflow of particles and magnetic field called the solar wind (SW). The Earth's magnetic field diverts that flow and protects us from these particles. A shock wave is built up between the Earth's magnetic field and the SW. This leads to a turbulent region called the Earth's magnetosheath. Within the magnetosheath, we regularly find faster or denser flows of particles, which we call jets. The formation of these jets is an active area of research. In this work we look at times where the Sun bursts out huge particle clouds (coronal mass ejections [CMEs]) and times when the SW is faster and piles up plasma like a snowplow. We look at how the particle clouds and the fast SW affect the jet generation. We compare conditions in the SW with CMEs and fast SW flow. We also examine the SW conditions during jet generation. CMEs decrease jet generation due to their strong magnetic fields and their magnetic field angles. This leads to changes in the properties of the bow shock unfavorable for jet generation mechanisms. The conditions in fast SW are more favorable, leading to more jet generation.