Magnetosheath Jets Over Solar Cycle 24: An Empirical Model

• Published in: Journal of geophysical research. Space physics 2023-08, Vol.128 (8), p.e2023JA031493-n/a
• Main Authors: Vuorinen, Laura, LaMoury, Adrian T., Hietala, Heli, Koller, Florian
• Format: Article
• Language: English
• Subjects: Computational Geophysics; Dynamic pressure; Electromagnetics; Empirical models; Fifteen Years of THEMIS Mission; Fourier Analysis; Informatics; Interplanetary magnetic field; Ionosphere; Ionospheric Propagation; Jets; Magnetic fields; Magnetopause; Magnetosheath; Magnetospheric Physics; Mathematical Geophysics; Natural Hazards; Nonlinear Geophysics; Nonlinear Waves, Shock Waves, Solitons; Oceanography: General; Radio Science; Remote Sensing and Electromagnetic Processes; Sampling; Saturn; Shock Waves; Solar cycle; Solar cycle-solar wind relationships; Solar wind; Solar wind parameters; Solar Wind/Magnetosphere Interactions; Solitons and Solitary Waves; Space Plasma Physics; Spacecraft; Spacecraft orbits; Spatial Analysis; Spatial Analysis and Representation; Spatial Modeling; Spectral Analysis; Wave Propagation; Wavelet Transform
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2023JA031493

Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft have been sampling the subsolar magnetosheath since the first dayside science phase in 2008, and we finally have observations over a solar cycle. However, we show that the solar wind coverage during these magnetosheath intervals is not always consistent with the solar wind conditions throughout the same year. This has implications for studying phenomena whose occurrence depends strongly on solar wind parameters. We demonstrate this with magnetosheath jets—flows of enhanced earthward dynamic pressure in the magnetosheath. Jets emerge from the bow shock, and some of them can go on and collide into the magnetopause. Their occurrence is highly linked to solar wind conditions, particularly the orientation of the interplanetary magnetic field, as jets are mostly observed downstream of the quasi‐parallel shock. We study the yearly occurrence rates of jets recorded by THEMIS over solar cycle 24 (2008–2019) and find that they are biased due to differences in spacecraft orbits and uneven sampling of solar wind conditions during the different years. Thus, we instead use the THEMIS observations and their corresponding solar wind conditions to develop a model of how jet occurrence varies as a function of solar wind conditions. We then use OMNI data of the whole solar cycle to estimate the unbiased yearly jet occurrence rates. For comparison, we also estimate jet occurrence rates during solar cycle 23 (1996–2008). Our results suggest that there is no strong solar cycle dependency in jet formation. Key Points Observed jet occurrence rates can be biased due to spacecraft orbits and uneven solar wind sampling We created a statistical model of jet occurrence using interplanetary magnetic field cone angle, magnitude, solar wind speed, and density There is no strong solar cycle dependency in jet occurrence, but there may be a ∼10%–20% decrease around solar maximum