Tailward stretching of geomagnetic field lines in the presence of an enhanced ionospheric convection electric field

When the interplanetary magnetic field turns southward, dayside reconnection leads to an increase of open magnetic flux and an increase of the electric potential drop across the polar cap. The enhanced electrostatic field in the ionosphere can be mapped to the closed field region of magnetotail, contributing to a dawn-to-dusk electrostatic component of electric field in the plasma sheet. In the presence of this driving electric field, an adiabatic evolution of the plasma sheet is formulated in A-space, where A is the magnetic flux function. It is found that the adiabatic evolution leads to the observed enhancement of the entropy content in the near-earth plasma sheet and to a tailward stretching of geomagnetic field lines. As a result, the cross-tail current in the near-earth plasma sheet is strongly enhanced.