Electromagnetic viscosity supported anomalous electric field in the electron diffusion region of collisionless magnetic reconnection.

Kinetic-scale electromagnetic fluctuations are frequently observed in the reconnection electron diffusion region. However, their potential to accelerate magnetic reconnection through anomalous effects remains a topic of debate, with a lack of direct in-situ observational evidence. Using the unprecedented high-resolution data from Magnetospheric Multiscale mission, we directly and systematically calculate the secular field-particle energy exchange rate and anomalous electric fields associated with electromagnetic fluctuations within 13 electron diffusion regions observed in Earth's magnetotail. Our findings reveal that the electromagnetic anomalous viscosity is the primary contributor to the anomalous electric field induced by electromagnetic fluctuations within the electron diffusion region. The maximum contribution of the anomalous viscosity can account for up to ~ 20% of the fast reconnection electric field, though it is typically less than 5% in most cases. We further find that locally growing electromagnetic fluctuations tend to accelerate reconnection, while locally damping electromagnetic fluctuations inhibit it. These results offer insights into the coupling between kinetic-scale electromagnetic fluctuations and magnetic reconnection in collisionless plasmas.