New Results Concerning Solar Wind Entry Into the Magnetosphere

A new book describes recent results defining the many pathways and foreshock, bow shock, magnetosheath, and magnetopause phenomena connecting the solar wind to the dayside magnetosphere.

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

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.

Origin of temperature anisotropies in the cold plasma sheet: Geotail observations around the Kelvin-Helmholtz vortices

To further our understanding of the solar wind entry across the magnetopause under northward IMF, we perform a case study of a duskside Kelvin-Helmholtz (KH) vortex event on 24 March 1995. We have found that the protons consist of two separate (cold and hot) components in the magnetosphere-like region inside the KH vortical structure. The cold proton component occasionally consisted of counter-streaming beams near the current layer in the KH vortical structure. Low-energy bidirectional electron beams or flat-topped electron distribution functions in the direction along the local magnetic field were apparent on the magnetosphere side of the current layer. We discuss that the bidirectionality of the electrons and the cold proton component implies magnetic reconnection inside the KH vortical structure. In addition, we suggest selective heating of electrons inside the vortical structure via wave-particle interactions. Comparing temperatures in the magnetosphere-like region inside the vortical structure with those in the cold plasma sheet, we show that further heating of both the electrons and the cold proton component is taking place in the cold plasma sheet or on the way from the vortices to the cold plasma sheet.