The jxB Forces Associated With Fast Flows in Earth's Magnetosphere and Magnetosheath

Abstract:

In Earth’s magnetotail the bursty bulk flows (BBFs) are accelerated by the magnetic tension of newly reconnected magnetic field lines. Closer in towards Earth, the tension is balanced by an increasing magnetic pressure gradient (as well as a thermal plasma pressure gradient). These forces can be seen as the result of interaction of the local currents associated with the flow structures and the magnetic field (including both the geomagnetic field, and the currents' self-generated field). This jxB force can be evaluated by a calculation of the current density j, using multi-spacecraft measurements.

We present Cluster multi-point measurements of BBFs showing the systematic behaviour of the jxB force with downtail distance. This provides important clues to the ultimate fate of BBF’s in the inner magnetosphere. We further present new results from MMS multi-point measurements of BBF events found using ExB drift velocity calculations. We report on the properties of the jxB forces of BBF events in the inner magnetosphere and near-Earth flanks.

Recently there has been an increased interest in localized flow velocity increases in the magnetosheath (here called ‘magnetosheath jets’), which have some similarities to BBFs. We present first results of the jxB forces associated with such magnetosheath jets, using MMS data.