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Zusammenfassung:
Magnetosheath jets are dynamic pressure enhancements that frequently emerge from the Earth's bow shock. Earthward propagating jets can traverse the magnetosheath and eventually impact the subsolar magnetopause. The occurrence of jets is strongly influenced by solar wind and interplanetary magnetic field (IMF) conditions. Most importantly, jets are known to occur significantly more often downstream of the quasi-parallel shock than the quasi-perpendicular shock. However, as the quasi-perpendicular configuration is more common at the Earth's bow shock, quasi-perpendicular jets can represent a significant fraction of jets. To better understand the solar wind influence on jet formation in these two different shock regimes, we use Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft magnetosheath observations and OMNI solar wind measurements to study jets in the subsolar magnetosheath separately during low and high IMF cone angles. We find that during low IMF cone angles (downstream of the quasi-parallel shock) jet occurrence near the bow shock is not sensitive to other solar wind parameters. However, during high IMF cone angles (downstream of the quasi-perpendicular shock) jet occurrence is higher during low IMF strength, low density, high beta, and high Alfvén Mach number conditions. This suggests that quasi-perpendicular shock dynamics amplified by higher beta and Alfvén Mach number can lead to formation of jets. As solar wind conditions vary throughout the solar cycle, we also present a statistical model of jet occurrence as a function of solar wind conditions and use it to estimate the yearly jet occurrence rates throughout solar cycle 24.
