Abstract

Magnetic reconnection converts magnetic energy into particle energy, with ion outflows being a prominent manifestation, particularly in geospace. Hall fields are indicators of rapid energy conversion in collisionless magnetic reconnection, yet the associated ion processes and signatures are not fully understood. Here, we analyze in-situ data and simulations to identify a distinct signature in the off-diagonal component of the ion pressure tensor. This signature displays a bipolar reversal that correlates with ion outflows across the reconnection X-line. The bipolar signal arises from a distorted velocity distribution during ion acceleration. Initially, Hall electric fields induce dawnward ion motion, which is followed by enhanced ion acceleration due to reconnection electric fields during cyclotron motion around the reconnected magnetic field. This interaction distorts the velocity distribution, producing the observed bipolar signals. The off-diagonal component of the ion pressure tensor reflects increased ion acceleration and energy conversion due to Hall electric fields.