1. Olga Khabarova 1, valentina zharkova 2 & vladimir kuznetsov 1
The solar wind plasma dynamics in the vicinity of the heliospheric current sheet
as observed at different heliocentric distances 2) 1)
Olga Khabarova 1, valentina zharkova 2 & vladimir kuznetsov 1
Problems of the results interpretation
secondary
main
Why?
1. Very often we observe several secondary density picks around the main peak at the sector boundary – Why?
2. Suprathermal electrons usually change their direction before the HCS indicted by magnetic field changes – Why?
3. The IMF, density and beta parameter are symmetrical regarding to the SBC, but the solar wind speed is not – Why?
The results of a superposed epoch analysis for the solar wind parameters
in the +/- 4 days vicinity around the SBC
(1322 cases according to the SBC list by Dr. Leif Svalgaard for January May 2011). OMNI2 daily solar wind data at 1 AU are used: a) IMF magnitude (B); b) solar wind density; c) beta plasma parameter; d) solar wind flow speed.
How to recognize a current sheet:
Bz~ -5nT
Azimuthal angle
The IMF magnitude
Bx=0
Speed
Density
Beta
The IMF magnitude falls down.
The in-ecliptic component of the IMF (Bx, GSE) = 0nT;
The azimuthal angle of the IMF (φB) changes by 180;
The solar wind speed slightly increases just at the moment of crossing the structure
Density increases significantly
Beta increases significantly
N < 4 1/cm3
Bz~ -3nT
Crossing of a thin sector boundary, the 3-second Wind SWE 3DP data:
a) IMF magnitude;
b) the in-ecliptic component of the IMF (Bx, GSE);
c) azimuthal angle of the IMF (φB);
d-f) spectrograms of the electron flux at the energies of
370 eV, 84 eV and 27 eV, respectively, as a function of pitch angle.
340 eV
84 eV
27 eV
Problems of the HCS indication
1 AU
Mismatches between sector boundaries identified in suprathermal electron pitch angle spectrograms and in magnetic field data alone.
Multiple sector boundary crossings (sometimes it lasts up to 6 days!)
Duration of sector boundary crossings at 1 AU for the period 1994 –2000 according to the ISTP Solar Wind Catalogue Candidate Events.
O. Khabarova, G. Zastenker, 2011, Solar Physics, 270, 311
N < 8 1/cm3
V> 600km/s Z Y X
(GSE)
(model)
Physical model for PIC
observations
Zharkova, V. V. & Agapitov, O. V. 2009, Journal of Plasma Physics, 75, 159
The HCS is suggested to undergo a continuous reconnection process.
The current sheet thickness is about a size of the proton gyroradius. The simulation region is made larger by a factor of to the both sides from the midplane.
Plasma particles in the PIC simulations are considered to generate their own electric and magnetic fields.
The background magnetic field is stationary during the whole simulation.
secondary
main
Density picks around the sector boundary
Suprathermal electorns’ behaviour
Electric field and velocity behaviour
bounced electrons
Peculiarities of the solar wind plasma behaviour around sector boundaries at 1 AU are most possibly resulted from the repeating, quasi-permanent magnetic reconnection at the HCS.
(Zharkova, Khabarova, ApJ, 2012).
The model of particle acceleration in the reconnecting heliospheric current sheet allows us:
to explain the observed asymmetric profiles of the solar wind velocity around the HCS by the proton motion along the polarisation electric field induced across the HCS by the separation of accelerated protons and electrons;
to reproduce the measured multi-peak distributions of plasma density across the HCS: a larger peak centered at the midplane being caused by the ’transit’ protons and the smaller ones being caused by the ’bounced’ protons;
to explain the observed changes in electron pitch-angle spectrograms at some distance from the HCS midplane by ’bounced’ electrons, forming the electron cloud in a form of a ’horse shoe’ (for the higher magnetic field ambient density) or of a ’locket’ (for the lower ones).
to interpret quantitatively the dependence on the guiding field magnitudes of the distances D between the location of a single SBC and the point where electrons change pitch angles by 180◦ by the acceleration of bounced electrons, which become more magnetized with the increase of the guiding magnetic field component.
V.Zharkova, O. Khabarova, Particle Acceleration in the Reconnecting Heliospheric Current Sheet: Solar Wind Data Versus 3D PIC Simulations, Astrophysical Journal, 2012, V.752, 1, 35
1. Primary density peak is a result of transit protons motion about the sector boundary. Secondary density peaks are due to bounce proton gyration.
2. Bounced electrons form a cloud near the current sheet.
3. The solar wind velocity profile is a result of the polarization electric field.
Ulysses
STEREO
1.5 AU
1.08 AU
0.96 AU
What happens at other distances?
Wind
ACE Re
Messenger – STEREO B - WIND – ACE –STEREO A - Ulysses
01-18 July 2007
Messenger
0.7 AU
STEREO
0.96 AU
1.08 AU
STEREO
WIND
ACE
1 AU
1 AU
It seems that the magnetic reconnection at the HCS occurs in a quasi-recurrent way.
The HCS structure becomes more and more complex not only with heliocentric distance, but also with time.
The same HCS, observed at very close distances, but at different longitudes, looks differ.