Monitoring the Spatio-temporal Evolution of a Reconnection X-line in Space

Inherently, magnetic reconnection - the process responsible for stellar flares and magnetospheric substorms - is very dynamic in space, owing to magnetic fluctuations and unsteady inflows. However, this process was always explained as a static picture in spacecraft measurements, neglecting the temporal evolution. This picture is not correct. Here we provide the first dynamic picture of magnetic reconnection in space, by monitoring the spatio-temporal evolution of a reconnection X-line at the magnetopause. Surprisingly, we find that the angle of a reconnection X-line can change from 44.°8 to 24.°9 during tens of milliseconds, which is significantly smaller than the characteristic timescale of the reconnection process (t = d i /V A ∼ 410 ms). Meanwhile, the spacecraft moves from the inflow region to the outflow region (spatial evolution). This result demonstrates that the magnetic reconnection in space can develop rapidly during tens of milliseconds, and thus that the concept of dynamic reconnection should be invoked instead of a static diagram.