The generalized Ohm’s law in collisionless magnetic reconnection

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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 Pxy(e) is also found to be proportional to the Dungey length scale, (meEy/eβ2)1/3, where β=∂Bz/∂x.