Magnetic reconnection at the Earth’s magnetopause is the process that changes the topology of geo-magnetic field lines creating open field lines along which the solar wind energy and momentum can flow into the magnetosphere.
The interplanetary magnetic field orientation (IMF) mainly determines the location and the orientation of the X-line. Moreover, it is found that reconnection is favoured by low values of plasma β in the adjacent magnetosheath.
A possible explanation for this β-dependence invokes the diamagnetic drift of the X-line (Swisdak et al. 2003). This drift occurs when a plasma pressure gradient across the magnetopause and a component of the magnetic field perpendicular to it (guide field) are present. Reconnection should be suppressed if the X-line drift motion exceeds the local Alfvén speed.
In this presentation, we examine a large number of dayside magnetopause observations of Double Star TC-1, which comprise reconnection events that satisfy the Walén relation and non-reconnection events. This dataset comprises also several reconnection events during which TC-1 is probably close to the X-line. Overall, these observations confirm that the diamagnetic drift is probably able to turn off the reconnection at the magnetopause.
Moreover, we used a subset of the reconnection events to study the X-line motion along the magnetopause when reconnection is not suppressed. It is found that generally the X-line drifts along the magnetopause northward or southward according to the sign of By. Furthermore, it seems that the velocity of the adjacent magnetosheath also contributes to the X-line motion.