Numerical simulation of the interaction of the plasma sheet with the lobes of the Earth's magnetotail

Abstract

Codes involving one and two spatial dimensions and three velocity dimensions are used to model the earth's magnetotail. It is shown that the magnetotail can become inflated as a consequence of low‐energy plasma convection toward the neutral plane. The two‐dimensional code shows the development of small‐scale turbulence. However, the growth of the turbulence appears limited and does not lead to substantial dissipation. A one‐dimensional model was used to simulate a particle population consisting of plasma sheet ions and cold lobe plasma. An applied convection electric field causes plasma sheet thinning and later expansion, consistent with observed substorm morphology. During the course of a simulated substorm the cold particles are heated and merge with the plasma sheet population. The magnetic field energy shows a slight increase, followed by a more rapid decrease as all of the cold particles are swept into the magnetotail. The code exhibits a conversion of both magnetic field energy and energy supplied by the convection electric field into particle energy. The simulations suggest that much of the magnetotail substorm morphology may be a simple consequence of an increase, followed by a decrease, in the convection electric field, without the requirement of any magnetospheric size scale plasma instability or other disruptive processes. It is also concluded that the presence of the convection electric field and a continuing replenishment of low‐energy particles in the magnetotail lobes are both necessary for maintenance of the magnetotail.

Ion tearing mode simulations with open boundary conditions

“…The open simulation model used here is an outgrowth of a periodic magnetostatic model used by Swift [1982Swift [ , 1983 Neumann conditions on Ay are therefore imposed at x = -x• and Lx + xb in order that the solution will continuously match the asymptotic field. This also implies that the magnetic field is normal to the x boundaries and that there can be no Poynting flux crossing these boundaries.…”

Ohm's Law for a current sheet

“…Numerical studies of the geomagnetic tail have not been solely restricted to MHD calculations, which require the use of an Ohm's law. In particular, Swift [1982Swift [ , 1983 investigated tail dynamics by simulating single-particle motion in the magnetic field obtained self-consistently from the particle motion. This approach gives j directly from the particle motion, and no Ohm's law need be assumed.…”