Geospace Plume and Its Impact on Dayside Magnetopause Reconnection

The role of cold plasma from a geospace plume in impacting magnetopause reconnection has been debated for a number of years with two contrasting theories proposed. A local control theory suggests that a plume decreases both local and global reconnection rates, whereas the global-control theory argues that the global reconnection rate is controlled by the solar wind rather than local physics. Observationally, point measurements by spacecraft cannot reveal whether a local change affects the global reconnection. A distributed observatory is hence needed to assess the validity of the two theories. We use THEMIS and LANL spacecraft to identify the occurrence of a geospace plume and its contact with the magnetopause. GPS TEC are used to trace global plume evolution and morphoology. We then use SuperDARN to monitor the location and the strength of dayside reconnection. By focusing on steady IMF conditions, our results show that as a plume contacts the magnetopause, the efficiency of reconnection is decreased at the contact longitude, whereas reconnection in the surrounding region is enhanced. The longitude region of suppressed reconnection spreads along the magnetopause with spreading of the plume along the magnetopause, and the region of the enhanced reconnection propagates so that it is always positioned adjacent to the longitude region of contact. Little variation is seen in the cross polar cap potential, implying that the global reconnection rate remains steady. The result is discussed in the context of the local- and global-control theory.