Scaling of the Rate of Asymmetric Magnetic Reconnection with Diamagnetic Effects

When asymmetric magnetic reconnection has an in-plane gas pressure gradient and an out-of-plane (guide) magnetic field, it is prone to diamagnetic effects in the plane of reconnection. This can make the X-line convect in the outflow direction, and reduce the reconnection rate or even suppress it completely. Evidence for the complete suppression of reconnection by this effect has been observed in the solar wind and Earth's magnetopause, and it has also been discussed as being important in the outer heliosphere, the magnetospheres of Jupiter, Saturn, and Mercury, and in magnetically confined fusion devices. It has also been shown that diamagnetic effects in asymmetric reconnection can act differently when set up by a density gradient compared to being set up by a temperature gradient. While it is known that reconnection that isn't suppressed can be slowed down by diamagnetic effects and that density and temperature gradients act differently, there is no quantitative prediction for the reconnection rate as a function of arbitrary upstream conditions. This work describes efforts towards that goal. We discuss a plausible model for the scaling of the reconnection rate when diamagnetic effects are included and compare predictions to particle-in-cell simulations. This study will be important in many settings, including reconnection in the solar wind and reconnection at planetary magnetospheres in reference to solar wind-magnetospheric coupling and the location of magnetic reconnection at the dayside magnetopause. It will also be useful for gaining perspective and making comparisons to Magnetospheric Multiscale (MMS) observations at the dayside.