valentina zharkova 1 and olga khabarova 2 1 - department of mathematics, university of bradford,...
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Valentina ZharkovaValentina Zharkova1 1 andand Olga KhabarovaOlga Khabarova22
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.
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
• 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.
Particle acceleration in a reconnecting current sheet (RCS)
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.
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 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.
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.
Behaviour of the solar wind parameters, measured by WIND MFI and SWE with 3-second resolution.
density
velocity
IMF longitudinal angle
Bx (horizontal) component of the IMF
The interplanetary magnetic field (IMF) strength
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.