On the gradient of electron pressure (stress) tensors in magnetotail reconnection

The reconnection electric field is an essential part in magnetic reconnection. In 2D symmetric magnetotail reconnection, the balance of this electric field is analyzed from the generalized Ohm’s law or the electron momentum equation, showing that electron off-diagonal pressure term plays an important role in the electron diffusion region in which electrons break the frozen-in condition. Previous studies have attributed this off-diagonal pressure term to agyrotropic meandering electrons. Here, we examine the gradient of electron pressure (stress) tensor term from the Vlasov equation, enabling a direction evaluation from electron distributions. Our results show that meandering electrons and inflow electrons can both contribute to the electron off-diagonal pressure (stress) term. Before inflow electrons reach to the central current sheet and become pitch angle mixed, they can be gradually demagnetized and decelerated, so the electron pressure (stress) gradient appears between the edge and central electron current sheet.