Investigation of the homogeneity of the energy conversion processes
atdipolarization fronts observed by MMSΑ
Abstract
In the present work, we consider four dipolarization front (DF) events
detected byMMS spacecraft in the Earth’s magnetotail during a substorm
on 23rd of July 2017between 16:05 and 17:19 UT. From their ion scale
properties, we show that thesefour DF events embedded in fast Earthward
plasma flows have classical signatureswith increases of Bz, velocity and
temperature and a decrease of density across theDF. We compute and
compare current densities obtained from magnetic and
particlemeasurements and analyse the Ohm’s law. We investigate the
energy conversionprocesses in the spacecraft frame via J.E calculations
averaged over the 4 spacecraft(s/c). We found both positive (loading)
and negative (generator) values +0.023nW/m3 at DF crossing, -0.043 nW/m3
after DF respectively. In ion and electronframes, the energy conversion
given by (J.(E+vexB)) or (J.(E+vixB)) values indicatesthat 4 s/c average
values are mostly negative whereas individual s/c values can bepositive
or negative. It suggests that the energy conversion is not homogeneous
atthe scale of the tetrahedron (electron scale). Finally we discuss the
origin of the nonhomogeneity of the energy conversion process by
computing the standard deviation(SD) of E and J (obtained from particle
measurement) normalized by their error bars.Larger SD for E than for J
suggest that the non homogeneity comes from the electricfield
fluctuations at the electron scale.