Transcript contribution

Valentina Zharkova1
and
Olga Khabarova2
1 - Department of Mathematics, University of Bradford, Bradford BD7 1DP, UK ([email protected] )
2 - Heliophysical Laboratory, IZMIRAN, Troitsk, Moscow reg., 142190 Russia ([email protected])
Problem formulation:
Many observational results of charge and velocity distributions of the solar
wind in the heliosphere reveal some very peculiar shapes which did not
have neither proper theoretical explanations nor compliances with many
numerical simulations. Many authors notices large magnetic field inversions
at sector boundaries (Kahler et al., 1996l Crooker et al. 1996, 2004) assuming
a presence of magnetic reconnection in the solar wind. However, the
conditions and scenarios of this reconnection were very poorly investigated.
The goal of this study is to find a model of magnetic interaction and particle
acceleration in the solar wind including the plasma feedback to a presence of
accelerated particles which is able to explain the observed behaviour of the
solar wind plasma parameters around the current sheets.
Behaviour of the solar wind parameters ( n - density; |B| - the IMF
averaged magnitude; V – velocity) and Kp – geomagnetic activity
index
(a–c) for 1300 events from January, 1964 to April, 2010 from the
SBC list by Leif Svalgaard,
(d–f) for 149 events of one-day sector boundaries crossings from
the ISTP Solar Wind Catalogue of Candidate Events for the period
1994–2000. Day zero corresponds to the day of sector boundary
crossing.
The strange asymmetric profiles of the solar wind
velocity V obtained from one day before to one day after
the sector boundaries crossings, revealed by Svalgaard
(1976) and recently confirmed by Khabarova and Zastenker
(2011) [2], remain unexplained.
Behaviour of the solar wind parameters, measured by WIND MFI
and SWE with 3-second resolution.
The interplanetary
magnetic field (IMF)
strength
Bx (horizontal) component of the IMF
IMF longitudinal angle
velocity
density
The solar wind velocity V
profiles around the current
sheets are determined by
the polarization electric
field E, induced by the
plasma feedback to
separation of accelerated
particles across the current
sheet caused by the
guiding field (Zharkova and
Gordovskyy, 2004).
• The acceleration of
protons and electrons in a
RCS is simulated with a
particle-in-cell (PIC) 2D3V
(two-dimensional in space
and three-dimensional in
velocity space) code for the
proton-to-electron mass
ratio of 100 and the
ambient density of 104 cm-3
(Siversky and Zharkova,
2009).
• The time scale of particle
acceleration is much
smaller than the typical
MHD time scales.
• The background
magnetic field which forms
an RCS does not evolve
during the particle
acceleration time.
The precise solar wind density Np
profile is asymmetric with rather
sharp edges occurring around the
main peak at the current sheet.
The simulation of a charge
density across the current sheet
shows the same profile, resulting
from a magnetic reconnection.
Particle acceleration in a reconnecting current sheet (RCS)
During magnetic
reconnection particles
are accelerated by a
drifted (reconnection)
electric field Ey and
are separated into
opposite halves from
the RCS midplane.
These separated
particles induce the
polarisation electric (E)
and magnetic (B) fields
in the directions x and
z.
B is much smaller than
the background field ,
but E is by order of
magnitude higher than
Ey.
• The similarity between the measured and simulated results can be explained by a non-stop (continuous) magnetic reconnection
process occurring at the heliospheric current sheet along all its length.
• The reconnection process with given magnetic topology is able to accelerate ambient particles of the opposite charges into the
opposite semiplanes from the RCS midplane creating the polarisation electric field. This field produces an asymmetric electron
current across the current sheet spatially defined by the reconnecting field topology.
• Further investigation is required into fitting specific measurements by the relevant model simulations.
1. Siverskyi T.V. and Zharkova V.V.: "The effect of magnetic topology on particle acceleration in a 3D reconnecting current sheet. I. PIC
approach", 2009, Journal of Plasma Physics, 75 (5): 619-636, Cambridge University Press, Cambridge, UK.
2. O.Khabarova, G.Zastenker. Sharp changes in solar wind ion flux and density within and out of current sheets. Sol. Phys., 2011, DOI:
10.1007/s11207-011-9719-4 http://arxiv.org/ftp/arxiv/papers/1006/1006.2487.pdf