Ion temperature anisotropy across a magnetotail reconnection jet

A significant fraction of the energy released by magnetotail reconnection appears to go into ion heating, but this heating is generally anisotropic. We examine ARTEMIS dual‐spacecraft observations of a long‐duration magnetotail exhaust generated by antiparallel reconnection in conjunction with particle‐in‐cell simulations, showing spatial variations in the anisotropy across the outflow far (>100d (i)) downstream of the X line. A consistent pattern is found in both the spacecraft data and the simulations: While the total temperature across the exhaust is rather constant, near the boundaries T (i,||) dominates. The plasma is well above the firehose threshold within patchy spatial regions at |B (X)|∈[0.1,0.5]B (0), suggesting that the drive for the instability is strong and the instability is too weak to relax the anisotropy. At the midplane ( [Formula: see text]), T (i,⊥)>T (i,||) and ions undergo Speiser‐like motion despite the large distance from the X line.