ON THE ROLE OF FLOW BURSTS IN THE ENERGY AND PARTICLE TRANSPORT IN THE MAGNETOTAIL

Abstract:

Recent observations have suggested that spatially localized flows of high temperature, low density plasma carrying a dipolarized magnetic field (dipolarizing flux bundles, DFB) play a key role in energy and plasma transport in the magnetotail. This study investigates how do thermodynamic parameters (such as density, temperature, pressure, specific entropy) and spectral properties of the DFB population depend on ambient plasma sheet properties and geocentric distance. By statistical analysis of 271 DFB events detected by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during the 2008-2009 tail seasons, we find that on average, plasma inside DFBs is a factor of 0.6 less dense and a factor of 1.5 to 2 hotter than ambient tail plasma. The radial profiles of average thermodynamic parameters inside and outside DFBs are similar; when fitted by the kappa-function, their energy spectra have similar kappa-exponents, but a factor of 2 larger peak energies
inside DFBs. Our analysis suggests that average DFB plasma properties are closely linked to those of the ambient plasma sheet population. Estimations show that on average, adiabatic heating of the ambient plasma in the increased magnetic field is the major factor in DFB plasma heating. These results suggest that the main role of fast-flow bursts accompanied the transient magnetic field dipolarizations (DFBs) is to introduce VxB electric field pulses that pick-up and energize ambient particles and transport energetic plasma towards the larger magnetic field.