Thermodynamic and Spectral Properties of the Dfb/Bubble Plasma Population in the Near-Earth Magnetotail

Abstract:

Numerous studies involving space-born and ground-based observations as well as
simulations have suggested that a few Earth's radii-wide narrow 
channels of fast plasma flow carrying a dipolarized magnetic field play the
key role in the magnetic flux, plasma, and energy transport in the magnetotail
and toward the inner magnetosphere. These structures were theoretically described as ``plasma bubbles''. Recently, the
term ``dipolairizing flux bundle'' (DFB) has been introduced to describe the
plasma bubble-like structure on the basis of local spacecraft measurements. 
We present statistical analysis of DFB observations by THEMIS probes during
2008 and 2009 tail-science seasons. The goal of this study is to understand how
the DFB plasma is energized and how its thermodynamic (density, temperature,
specific entropy, and bulk velocity) and spectral properties depend on the
geocentric distance. To achieve this goal, 271 events observed at radial
distances from ~7 to 25 RE downtail were selected. We compare i) the
thermodynamic parameters and energy spectra inside DFBs with those in the
ambient plasma sheet and ii) the thermodynamic parameters and the spectra
inside DFBs observed at different geocentric distances.