Cold and Dense Plasma Sheet Caused by Solar Wind Entry: Direct Evidence

Abstract

We present a coordinated observation with the Magnetospheric Multiscale (MMS) mission, located in the Earth’s magnetotail plasma sheet, and the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) mission, located in the solar wind, in order to understand the formation mechanism of the cold and dense plasma sheet (CDPS). MMS detected two CDPSs composed of two ion populations with different energies, where the energy of the cold ion population is the same as that of the solar wind measured by ARTEMIS. This feature directly indicates that the CDPSs are caused by the solar wind entry. In addition, He+ was observed in the CDPSs. The plasma density in these two CDPSs are ~1.8 cm−3 and ~10 cm−3, respectively, roughly 4–30 times the average value of a plasma sheet. We performed a cross-correlation analysis on the ion density of the CDPS and the solar wind, and we found that it takes 3.7–5.9 h for the solar wind to enter the plasma sheet. Such a coordinated observation confirms the previous speculation based on single-spacecraft measurements.

Dipolarization Fronts in Cold‐Dense and Hot‐Tenuous Plasma Sheet Conditions: A Comparative Study

“…Across the DF, weak change of electron/ion temperature (Figures 2c and 2d) and electron/ion energy spectrum (Figures 2e and 2f) was observed, note that the normal of DF was directed earthward; the weak change may be responded to the spatial effect (Runov et al., 2013). According to our previous study, the cold particles inside the DF and ambient CDPS may originate from the solar wind, because their energy range (Figures 3b and 3c in Yu et al., 2020) were consistent with the solar wind particle properties.…”

Magnetic Field Gradient Across the Flank Magnetopause

“…This cold and dense plasma sheet occurs after several hours of northward IMF and is observed predominantly along the flanks and at high magnetic latitudes (e.g., Fujimoto et al, 1998) as a result of double cusp or lobe reconnection at the dayside (e.g., Song and Russell, 1992;Sandholt et al, 1999;Lavraud et al, 2006) or enters from the flanks through Kelvin-Helmholtz instability (Sorathia et al, 2019). According to Yu et al (2020), the cold and dense plasma sheet probably contributes to the production of stormtime energetic particles (Borovsky et al, 1997) and can result in stronger ring currents during the main phase of storms (e.g., Lavraud et al, 2006) and can also lead to the mass loading of the magnetotail. Therefore, it may have effects on substorms (e.g., Fu et al, 2012) and reduction of the reconnection rate (e.g., Toledo-Redondo et al, 2016).…”