The generalized Ohm's law in collisionless magnetic reconnection

The generalized Ohm's law and the force balance near neutral lines in collisionless magnetic reconnection is studied based on two-dimensional full particle simulations in'which the ion-electron mass ratio is set to be 1836. The off-diagonal elements of a plasma pressure tensor are found to be responsible for the breakdown of the frozen-in condition in collisionless reconnection. While the off-diagonal elements of the electron pressure tensor are dominant terms in the generalized Ohm's law near neutral lines, the ion off-diagonal pressure terms are of significant importance when ions are main current carriers. The spatial scale of electron off-diagonal pressure term P-xy((e)) is also found to be proportional to the Dungey length scale, (m(e)E(y)/e beta(2))(1/3), where beta=partial derivative B-z/partial derivative x. (C) 1997 American Institute of Physics.