ICS-13 Abstract View


Forces acting on the bursty bulk flow plasma - Cluster and MMS results
Karlsson, T., tomas.karlsson@ee.kth.se (1)
Lindqvist, P.-A., per-arne.lindqvist@ee.kth.se (1)
Kullen, A., anita.kullen@ee.kth.se (1)
The fate of bursty bulk flows (BBFs) as they reach the inner magnetosphere is unclear. To understand the BBF dynamics in the inner tail, we need to know what forces act on the BBF plasma. The relation between the magnetic (jxB) and thermal plasma pressure forces (-grad p) determines if that plasma is accelerated or braked. With Cluster multi-point measurement the magnetic force was determined for 67 BBF events. It was shown that the magnetic tension force was consistently directed towards Earth, whereas the magnetic pressure gradient force increased in magnitude closer in to Earth, and was all the time directed tailwards. This resulted in a net acceleration for X_GSE < -14 R_E, while the magnetic force braked the plasma closer to Earth. Since the magnetic pressure gradient could not be determined locally, this result was a step towards understanding the dynamics, but an incomplete result. With the high-quality MMS particle data it is possible to determine the local plasma pressure gradient, and add an important piece of the puzzle. We will present examples of the full force balance between pressure and magnetic forces on a number of BBF events in the inner magnetosphere. A third factor may also important in determining the BBF dynamics: radiation losses from plasma wave emissions. We will show some preliminary estimates of the importance of this effect.
(1) Space and Plasma Physics, School of Electrical Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden