The driving of the plasma sheet by the solar wind

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) By in the plasma sheet is strongly correlated with the By in the solar wind, (5) Bz in the plasma sheet is weakly correlated with the Bz in the solar wind, (6) Ey in the plasma sheet is weakly correlated with the Ey 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.