Transcript Collisional Shocks: in situ studies of astrophysical

Scales at High Mach Number
Quasiperpendicular Shocks and
Problem of Electron Heating
Vladimir
KRASNOSELSKIKH
LPC2E / CNRSUniversity of Orleans
S.J. Schwartz,
D. Sundqvist, F. Mozer
Electron Heating Scale at High Mach Number
Quasiperpendicular Shocks
Plan
Introduction
1. Shock front structure
2. Small scale structure of the electric
and magnetic fields
3. Scale of electron heating
4. Conclusions
Collisionless shocks : Critical questions
Quasiperpendicular shock
Thermalisation Variability
scales
electrostatic
potential
ion reflection
species
partition
fine structure
Particle Acceleration
structure
(ripples ?)
response to
upstream
conditions
nonstationarity
ion
acceleration
electron
acceleration
Collisionless shocks : new results from Cluster
Earth’s bow shock
Tsurutani and Rodriguez, 1981
Magnetospheric regions studied by Cluster
Bow shock
Polar cusp
Auroral zone
Solar wind
Plasmasphere
Magnetopause
Initial idea of the shock front structure: dispersion versus nonlinearity in
the presence of the weak dissipation
Precursors in sub-critical shocks and early models (Sagdeev, 1961, 1964)
The structure is formed as a result of counter-balance between
nonlinearity and dispersion in the presence of the weak dissipation
Quasiperp Shock profile
(heritage of ISEE)
As supposed for subcritical shocks
ISEE and simulations: supercritical quasi-perpendicular shocks:
the dissipation is due to reflected ions
How does it change the role of the dispersion and nonlinearity?
If shock structure is similar to dispersive nonlinear waves then
Phase velocity
dependence of
oblique fast
magnetosonic
(whistler) waves upon
the wavenumber
Galeev et al., 1988 a,b,c; Krasnoselskikh et al. 2002
Gradient catastrophe of nonlinear upstream whistler
Above whistler critical Mach number whistler precursor becomes nonlinear
Nonlinear whistler critical Mach number
M nw
| cos  Bn |

(2me / mi )1/ 2
Above Mnw shock nonlinear steepening of waves can not be
stopped anymore by dispersion and/or dissipation and
becomes non-stationary
Appeal to experimental data of multi-point
measurements: Cluster
What are the right questions to answer making
use of the data?
• Does the front steepen with the growth of the Mach number till
the scales comparable with electron inertial length?
• What are the characteristic scales of fine structure of the shock
front?
• What are the sources of waves observed upstream of the
ramp?
• Can we observe direct manifestations of the overturning and
reformation?
The answer can be found analysing scales and energy fluxes.
What is the scale of the major transition?
Is the region of strongest gradient
determined by the dispersion –
nonlinearity effects?
Dispersive model:
precursor and ramp transition
are determined by dispersionnonlinearity and scales as
several c/ωpe
(electron inertial length)
Magnetic field ramp thickness (Hobara et al, 2010)
Magnetic field ramp grasient (Hobara et al.,
2010)
Magnetic ramp thickness statistics (Mazelle et al., 2010)
PRL, 2012
2012
PRL, 2012
Electron heating (Schwartz et al., 2011)
Electron heating (Schwartz et al., 2011)
Electron heating (Schwartz et al., 2011)
Electric field on the interval 22:15:30-22:15:40
More details 22:15:33-22:15:34
Sundkvist et al., AGU 2012
• The heating can be super-adiabatic as
well as sub-adiabatic
• Parallel and perpendicular
temperatures grow on the same time
scale
• The process is determined by the
presence of the small scale electric
field bursts
Small scale jumps of the electric field
• Thank you for your attention
• More details on seminar in September