Download Zharkova & Khabarova, ApJ (2012)

11th European Space Weather Week. Recent Advances in Space Weather Science
Dynamics of particles in the vicinity
of the heliospheric current sheet:
observations versus theory
Olga Khabarova 
Valentina Zharkova

Gang Li
Pushkov Institute of terrestrial
magnetism and radiowave
propagation (IZMIRAN),
University of
Northumbria, Newcastle
Upon Tyne,
CSPAR, University of
Alabama in Huntsville,
Russia
United Kingdom
USA
[email protected]
Olga Khabarova  Valentina Zharkova

Gang Li
• Behaviour of particles in a vicinity of reconnecting
current sheets in the solar wind:
- theoretical points of view; PIC-modelling
- observations
 Theoretical aspects of particle acceleration due to
magnetic island dynamics in the solar wind
• Combination of theoretical ideas. An application of a
new paradigm to explanation of observations.
Siversky, Zharkova, JPP, 2009; Zharkova,Gordovsky, ApJ, 2004; Zharkova,Agapitov, JPP, 2009
(Verboncouer & Gladd, 1995)
Vinflow  0.01 Valfven
Drift electric field
In order to avoid numerical
instabilities in the PIC code
(Verboncoeur et al. 1995), the
following constrains are to be
satisfied
Δt is the time step,
Δξ is the grid step
in any direction
Siversky, Zharkova, JPP, 2009; Zharkova,Gordovsky, ApJ, 2004; Zharkova,Agapitov, JPP, 2009
Trajectories of electrons and protons near the
reconnecting current sheet.
bounced proton
transit proton
Proton trajectories are shown in red, and electron trajectories are shown in blue.
Separation of opposite charged particles around the current sheet
leads to the occurrence of a strong electric field
Siversky, T. V., & Zharkova, V. V. 2009, J.Plasma Phys., 75, 619
HXR and γR imaging
2.223 MeV footpoints (ions)
on opposite sides of the
flaring loop arcade are
displaced from the
corresponding 0.2–0.3 MeV
footpoints (electrons).
Hurford et al., 2006 ApJ
HCS
electrons
protons
A regular structure of the heliospheric current sheet
A 3D reconstructed velocity plot, from the viewpoint of a
remote observer (STEL data).
X
(GSE)
observations
Z (GSE)
Z (GSE)
Y
Z
Y
X (GSE)
(model)
X
Z
Y (GSE)
• 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 10-100 to the both sides from the midplane.
• The background magnetic field is stationary during the whole simulation.
• Plasma particles in the PIC simulations are considered to generate their own electric
and magnetic fields.
Zharkova, Khabarova, Astrophysical Journal, 752, 1, 35 (2012)
10-6
Zharkova, Khabarova, ApJ, 2012; Khabarova, Zastenker, SolPh 2011
340 eV
84 eV
27 eV
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.
Zharkova, Khabarova,
ApJ, 2012
Density=100 cm-3
Bz0=10-8T
Density=10 cm-3
Bz0=10-8T
By=0.1Bz0
Bx=-0.02Bzo
By=0.01Bz0
Bx=-0.02Bzo
Density=100 cm-3
Bz0=10-9T
By=0.01Bz0
Bx=-0.002Bzo
Density=10
cm-3
10 cm-3
Bz0=10-9T
By=0.1Bz0
Bx=-0.02Bzo
Zharkova, Khabarova, ApJ, 2012
The results can solve the problem of mismatches between polarity reversal
signatures in suprathermal electron pitch angle spectrograms and changes
of azimuth angle of the magnetic field.
Kahler, Lin (Geophys. Res. Lett., 1994); Crooker, Kahler, Larson, Lin (J.
Geophys. Res., 2004)
The main idea of the [Zharkova & Khabarova, ApJ (2012)] paper:
small- and medium-scale features of the IMF and plasma characteristics
observed near the HCS may be explained simultaneously only if magnetic
reconnection was assumed to occur simultaneously and re-currently in
many places on the HCS.
Acceleration of particles in current sheets due to magnetic reconnection
(Zelenyi et al., 2013; Drake et al. 2010, 2013; Büchner et al, 2010; Lapenta
2012 etc.).
Energization of particles up to MeV in the Earth’s magnetotail [Zelenyi,
Lominadze & Taktakishvili (1990); Ashour-Abdalla et al. (2011) ], but it is still
disputable for the HCS, because of some lack of observations.
It is furthermore believed that there no particle acceleration in the keVMeV range is associated with the magnetic reconnection exhausts in the
solar wind, i.e. there is no significant local acceleration at the reconnecting
HCS [Gosling et al. (2005)].
Goldstein, Matthaeus & Ambrosiano (1986): the maximum energy
achievable during the magnetic reconnection at the HCS should be ~100
keV.
Zharkova & Khabarova (2012; 2014): the maximum energy achievable
during the magnetic reconnection at the HCS may be ~ MeV.
Theory: tearing instability of current sheets
leads to magnetic island formation
Theory: magnetic island contraction and
merging can accelerate particles
The dominant charged particle
energization processes are
1) the electric field induced by
magnetic island merging,
2) magnetic island contraction.
In both cases, the magnetic island
topology ensures that charged
particles are trapped in regions
where they can experience
repeated interactions with either the
induced electric eld or contracting
magnetic islands.
Zank G.P., le Roux J.A., Webb G.M.,
Dosch A., & O. Khabarova.
Drake et al, 1998, 1999, 2006,
Daughton et al, 2011
Particle acceleration via reconnection
processes in the supersonic solar wind.
Astrophysical Journal, V.797, 2014
Small-scale magnetic island formation
predominantly occurs near the HCS
Particles can be
accelerated at least to
keV energies at the
HCS
and re-accelerated in
dynamically changing
magnetic islands near
the HCS
Cartwright, M. L., and M. B. Moldwin (2010),
Heliospheric evolution of solar wind small-scale
magnetic flux ropes. J. Geophys. Res., 115, A08102
A specific form of the HCS (ripples on
the HCS) is favorable for keeping
magnetic islands and particle
acceleration to high energies
Small-scale magnetic islands in the solar wind and their role in
particle acceleration. Part 1: Dynamics of magnetic islands near
the heliospheric current sheet.
Khabarova, Zank, Li, le Roux, Webb, Dosch, submitted to ApJ
ACE
WIND
ACE and WIND spacecraft
were 150 Re apart.
A clear magnetic field vector
rotation is seen in magnetic
islands, that occurs
simultaneously with energetic
particle flux increases
Khabarova, Zank, Li, le Roux, Webb, Dosch, submitted to ApJ
Particle acceleration associated with islands near the HCS (an after -CME event)
Khabarova, Zank, Li, le Roux, Webb, Dosch, submitted to ApJ
Magnetic reconnection
a) at the leading edge of an ICME;
b) behind the ICME
Particle acceleration associated with islands near the HCS (a pre-CME event)
Khabarova, Zank, Li, le Roux, Webb, Dosch, submitted to ApJ
Particle acceleration associated with islands near the HCS (a pre-CME event)
Khabarova, Zank, Li, le Roux, Webb, Dosch, submitted to ApJ
Olga Khabarova ([email protected])
Valentina Zharkova
Gang Li
•
A magnetic
reconnection is a
re-currently
ongoing process
that takes place at
the heliospheric
current sheet
(HCS) .
•
The separation of
particles of the
opposite sign
during the
magnetic
reconnection at
the HCS leads to
strong particle
acceleration
• The local energetic
particle flux
enhancements might
be explained by
particle energization
occurring near the
HCS during dynamical
evolution of secondary
current sheets and
small-scale magnetic
islands.
• These structures are
supposed to trap and
re-accelerate particles
(initially accelerated at
the HCS) up to
MeV/nucleon.
• Effectiveness of this
process depends on
the topology of the
HCS (ripples) .