Experimental study of nonlinear interaction of plasma flow with charged thin current sheets: 1. Boundary structure and motion
Other literature type
Marcucci, M. F.
Bogdanova, Y. V.
Décréau, P. M. E.
Rauch, J. L.
Trotignon, J. G.
(issn: 1607-7946, eissn: 1607-7946)
We study plasma transport at a thin magnetopause (MP), described hereafter
as a thin current sheet (TCS), observed by Cluster at the southern cusp on
13 February 2001 around 20:01 UT. The Cluster observations generally agree
with the predictions of the Gas Dynamic Convection Field (GDCF) model in the
magnetosheath (MSH) up to the MSH boundary layer, where significant
differences are seen. We find for the MP a normal roughly along the GSE x-axis,
which implies a clear departure from the local average MP normal, a
~90 km thickness and an outward speed of 35 km/s. Two populations are
identified in the MSH boundary layer: the first one roughly perpendicular to
the MSH magnetic field, which we interpret as the "incident" MSH plasma,
the second one mostly parallel to <b>B</b>. Just after the MP crossing a
velocity jet is observed with a peak speed of 240 km/s, perpendicular to
<b>B</b>, with <i>M<sub>A</sub></i>=3 and β>10 (peak value 23). The magnetic field clock angle rotates by 70°
across the MP. <i>E<sub>x</sub></i> is the main electric field component on both sides
of the MP, displaying a bipolar signature, positive on the MSH side and
negative on the opposite side, corresponding to a ~300 V electric
potential jump across the TCS. The <i>E</i>×<i>B</i> velocity generally
coincides with the perpendicular velocity measured by CIS; however, in the
speed jet a difference between the two is observed, which suggests the need
for an extra flow source. We propose that the MP TCS can act locally as an
obstacle for low-energy ions (<350 eV), being transparent for ions with
larger gyroradius. As a result, the penetration of plasma by finite
gyroradius is considered as a possible source for the jet. The role of
reconnection is briefly discussed. The electrodynamics of the TCS along with
mass and momentum transfer across it are further discussed in the companion
paper by Savin et al. (2006).