The driving of the plasma sheet by the solar wind

TLDR

The plasma sheet is likened to a high‑Reynolds‑number fluid wake. The study statistically couples the plasma sheet to the solar wind by comparing simultaneous measurements from satellite pairs in the solar wind and in the magnetotail or near‑Earth plasma sheet. The plasma sheet’s density, temperature, pressure, and magnetic field components are strongly correlated with corresponding solar‑wind parameters, with time lags of 2–15 h, and mass transport is suggested to occur rapidly up the tail via the boundary layer followed by poloidal convection or eddy diffusion, while removing solar‑wind effects diminishes geomagnetic activity correlations.

Abstract

The coupling of the plasma sheet to the solar wind is studied statistically using measurements from various satellite pairs: one satellite in the solar wind and one in either the magnetotail central plasma sheet or the near‐Earth plasma sheet. It is found that the properties of the plasma sheet are highly correlated with the properties of the solar wind: specifically that (1) the density of the plasma sheet is strongly correlated with the density of the solar wind, (2) the temperature of the plasma sheet is strongly correlated with the velocity of the solar wind, (3) the particle pressure and total pressure of the plasma sheet are strongly correlated with the ram pressure of the solar wind, (4) B y in the plasma sheet is strongly correlated with the B y in the solar wind, (5) B z in the plasma sheet is weakly correlated with the B z in the solar wind, (6) E y in the plasma sheet is weakly correlated with the E y in the solar wind, and (7) plasma sheet earthward‐tailward flow velocity is weakly anticorrelated with the solar wind velocity. After removing these solar wind dependencies, the dependencies of the properties of the plasma sheet on geomagnetic activity are reduced and changed. The time lags between the solar wind density and the plasma sheet density are investigated statistically and on a case‐by‐case basis; it is found that solar wind material reaches the midtail plasma sheet in ∼2 hours, reaches the near‐Earth nightside plasma sheet in ∼4 hours, and reaches the dayside plasma sheet in ∼15 hours. The pathway for mass transport into the plasma sheet is explored; it is suggested that solar wind material is transported rapidly up the tail to the near‐Earth region via the plasma sheet boundary layer, followed by poloidal transport via convection in the near‐Earth (low β) plasma sheet or followed by eddy diffusion in the not‐too‐distant (high β) plasma sheet. Analogies are drawn between the high Reynolds number plasma sheet and a high Reynolds number fluid wake.