Bursty Bulk Flow Braking and the Role of Turbulence

Tuesday, 16 December 2014
Julia E Stawarz, Robert Ergun and Katherine Goodrich, University of Colorado at Boulder, Boulder, CO, United States
Bursty Bulk Flows (BBFs) play an important role in the transfer of mass and energy from distances of roughly 20 RE or greater into the near earth plasma sheet. The braking region at around 10 RE where the flows are slowed and/or deflected is an important region in understanding the energy transfer in the magnetotail. From the BBF braking region energy can be transferred out of the region through Alfvén waves that propagate along the field lines to the aurora and deflected flow around the Earth and/or be dissipated by processes within the region itself and adiabatic heating of particles. Observational evidence is presented from the THEMIS spacecraft showing that BBF braking events are associated with enhanced electric field activity, which can reach up to ~500 mV/m. The Electric field activity is shown to contain nonlinear structures that are suggestive of the presence of field-aligned currents. Magnetic field activity is also found that appears to be Alfvénic in nature and have Poynting fluxes up to 1 mW/m2. A theory is considered in which turbulence in the BBF braking leads to the development of field-aligned currents that can destabilize into the observed nonlinear structures and thus provides a mechanism for the dissipation of BBF energy. The role of turbulence in facilitating the excitation of Alfven waves in the BBF braking region that can propagate out of the region and lead to Alfvénic aurora is also examined.