Impacts of Magnetosheath High‐Speed Jets on the Magnetosphere and Ionosphere Measured by Optical Imaging and Satellite Observations

Abstract

Magnetosheath high-speed jets (HSJs) are dayside upstream transient disturbances with enhanced flow velocity and dynamic pressure. They are associated with significant magnetopause perturbations, ultralow frequency waves in the dayside magnetosphere, and localized flow enhancements in the ionosphere. However, whether HSJs have corresponding dayside aurora signatures is still an open question. If auroral signatures are found, 2-D structure and evolution of HSJ effects on the magnetosphere can be imaged in a much higher precision than possible by other means. In this study, eight HSJ events are identified by the THEMIS satellites located within ±1 MLT of the center of the field-of-view of the South Pole station all-sky imager. In all of those cases, the HSJs are observed to have a nearly one-to-one relationship with individual localized discrete/diffuse auroral brightenings. The azimuthal size of HSJ-related diffuse aurora signatures is~800 km at 230-km altitude in the ionosphere and~3.7 Re in the magnetosphere, which is slightly larger but of the order of the cross-sectional diameter of HSJs (~1 Re). Furthermore, most of those aurora signatures have azimuthal motion, whose magnitude and direction agree with magnetosheath background flows. This study for the first time shows high-resolution, two-dimensional observations of localized structure and fast propagation of precipitation due to magnetosheath HSJs. We conclude that magnetosheath HSJs can have substantial impacts on the coupled magnetosphere-ionosphere system, causing localized magnetospheric compression and aurora brightening, in a similar manner to responses during interplanetary shocks except with a smaller scale size. Recent papers show that HSJs tend to occur when the IMF cone angle is low, especially less than 40°( Plaschke et al., 2013). Hietala et al. (2009) suggested that HSJs are probably generated due to the ripples of the quasi-parallel bow shock, and a quantitative study shows that 97% of the observed HSJs can be

Classifying Magnetosheath Jets using MMS - Statistical Properties

“…To summarize, our results suggest that the quasi-parallel and the boundary jets are the classes connected to jet-related phenomena, such as the throat aurora (Han et al, 2017;Wang et al, 2018), magnetopause reconnection (Hietala et al, 2018) and possibly the radiation belts (Turner et al, 2012;Xiang et al, 2016). Finally, both Qpar and boundary jets exhibit high earthward velocities and duration, making them important to investigate magnetosphere coupling phenomena and geoeffective properties.…”

“…Furthermore, they can affect the radiation belts through the loss of outer belt electrons, (Turner et al, 2012;Xiang et al, 2016). Additionally, jets can affect the aurora via the mechanism of "dayside throat aurora" which has been connected to magnetosheath particle precipitation (Han et al, 2017;Wang et al, 2018). The link between jets and energy transfer through the magnetosphere was also observed recently when surface eigenmodes were found to be excited through a collision between a jet and the magnetopause (Archer et al, 2019).…”

Jets in the magnetosheath: IMF control of where they occur

“…For example, Hietala et al (2018) published observational evidence of a jet triggering magnetic reconnection at the dayside magnetopause. Wang et al (2018) showed direct correspondence between magnetosheath jets and diffuse and discrete auroral brightenings. The newly observed magnetopause surface eigenmodes (standing waves) were also excited by a jet colliding into the magnetopause (Archer et al, 2019).…”

Electron Acceleration by Magnetosheath Jet‐Driven Bow Waves

“…Such compression can also excite eigenmodes of the magnetopause surface (Archer et al, 2019). The perturbation on the magnetopause surface can then result in compressional low-frequency waves within the magnetosphere, ionospheric flow enhancements, and auroral brightening (e.g., Archer et al, 2013;Hietala et al, 2012;Wang et al, 2018).…”