|
|
 |
|
|
Ann. Geophys., 26, 1559-1566, 2008
www.ann-geophys.net/26/1559/2008/
© European Geosciences Union 2008
Observation of three distinct ion populations at the Kelvin-Helmholtz-unstable magnetopause
M. G. G. T. Taylor1 and B. Lavraud2,*
1ESTEC/European Space Agency, Noordwijk, The Netherlands
2Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
*now at: Centre d'Etude Spatiale des Rayonnements, CNRS, Toulouse, France
Abstract. We report Double Star spacecraft observations of the dusk-flank magnetopause
and its boundary layer under predominantly northward interplanetary magnetic
field (IMF). Under such conditions the flank low-latitude boundary layers
(LLBL) of the magnetosphere are known to broaden. The primary candidate
processes associated with the transport of solar wind plasma into the LLBL
are: (1) local diffusive plasma transport associated with the
Kelvin-Helmholtz instability (KHI), (2) local plasma penetration owing to
magnetic reconnection in the vicinity of the KHI-driven vortices, and (3)
via a pre-existing boundary layer formed through double high-latitude
reconnection on the dayside. Previous studies have shown that a cold
population of solar wind origin is typically mixed with a hot population of
magnetospheric origin in the LLBL. The present observations show the
coexistence of three distinct ion populations in the dusk LLBL, during an
interval when the magnetopause is unstable to the KHI: (1) a typical hot
magnetospheric population, (2) a cold population that shows parallel
temperature anisotropy, and (3) a distinct third cold population that shows
perpendicular temperature anisotropy. Although no unambiguous conclusion may
be drawn from this single event, we discuss the possible mechanisms at work
and the origin of each population by envisaging three likely sources: hot
magnetospheric plasma sheet, cold magnetosheath of solar wind origin, and
cold plasma of ionospheric origin.
Full Article in PDF (1090 KB) |
|
|
