MMS observations of strong plasma enhancements at the dawn terminator

On March 7, 2016, the MMS constellation traveled from the nightside to the dayside of the inner magnetosphere. At the dawn terminator ( 6 am MLT) the four MMS spacecraft detected several significant plasma enhancements accompanied by strong plasma acceleration. The strongest event was captured by MMS in burst mode (30 ms for electron and 150 ms for ions). The number density abruptly increased from typical magnetospheric background values, 1 cm-3, up to 50-60 cm-3. The solar wind parameters corresponding to these enhancements are quite stable without any sharp changes. Specifically, the plasma dynamic pressure is steady close to nominal at 2.5-3 nPa and the IMF BZ component is stable and slightly negative -2 to -3 nT indicating that the more obvious solar wind drivers are absent for such an extreme event. The estimated distance from the nominal magnetopause to the spacecraft was 3 RE (from the Shue model), and the data does not show characteristics of multiple magnetopause crossings. Looking more broadly however, it appears that these events occurred during the recovery phase of quite strong magnetic storm as confirmed by the DST profile on March7, 2016. For this presentation, we combine the MMS observations with results of global MHD simulations to understand which one of several possible scenarios might explain MMS observations: either set of the Flux Transfer Events (FTE) resulting from the dayside reconnection or earthward-propagating dipolarization fronts caused by the tail reconnection.