initiation evolution coronal shock...
TRANSCRIPT
INITIATION AND EVOLUTIONOF
CORONAL SHOCK WAVES
B. Vršnak, T. Žic, S. Lulić(Hvar Obs.)
N. Muhr, A. Veronig, M. Temmer, I. Kienreich(Uni.-Graz)
This work has been supported in part by Croatian Scientific Foundation
under the project 6212 „Solar and Stellar Variability“ (SOLSTEL).
Observational signatures
� Type II radio bursts(Wild & McCready 1950, Aust.J.Phys. 3, 387)
� Moreton waves(Moreton & Ramsey 1960, PASP 72, 357)
KSO
EUV, SXR, He I, coronograph, radio,...
EIT/SoHO
Yohkoh
NRH
270
290
310
330
350
45 50 55 60 65 70 75 80
151 MHz
164 MHz
237 MHz
327 MHz
Ha/EIT
t (min after 09:00 UT)
F
CME
b)
EIT/SoHOMLSO
Domain / Signature
Corona- radio type II- WL fronts, streamers
IP(radio, WL)
in situ
Low Corona(EUV)
Upper Chromosphere & TR(Hα, HeI, …)Moreton, disturbed filaments, …
timing, kinematics, intensity, spectral, morphology, …
Terminology
bowshock
pistonshock
blas
t-sho
ck
shoc
k
bow
-sho
ck
piston piston
< <> >Vp V0 Vp V
0
Vp > V0
Vsh >Vp
Vsh =Vp
Vsh >Vp
projectile
Large-amplitude wave (shock)
� impulsive plasma motion perpendicular to the magnetic field ("strong" acceleration)
� large amplitude wavefront is created� shock forms after certain time/distance due to the
nonlinear evolution of the perturbation (signal velocity
0
0.1
0.2
0.3
0.4
0 1 2 3 4X-X0
U
nonlinear evolution of the perturbation (signal velocity depends on the amplitude!)
w(t) = w0 + k u(t)
k=4/3, w0=cs0 at β >> 1k=3/2, w0=vA0 at β << 1
u wu
w
vA0
xxf
0)( 23
0 =∂∂++
∂∂
x
uuv
t
u
Piston Mechanism (simulations)
0.0
0.5
1.0
1.5
2.0
0 0.1 0.2 0.3
v
t- amplitude growth + steepening � shock formation
- after t~0.15 ~const. amplitude/velocity
1D - planar
0
0.1
0.2
0.3
0.4
0.5
0 0.1 0.2 0.3
x
t
wave
piston
2D - cylindrical
- amplitude growth + steepening � shock formation
- lower amplitude, formation of rarefaction region
- after t~0.08 decreasing amplitude/velocity
0
0.1
0.2
0.3
0.4
0.5
0 0.1 0.2 0.3
x
t
dip
-0.2
0.2
0.6
1
1.4
0 0.1 0.2 0.3
v
t
2.5-D MHD simulation
BφBz By
+
β = 00.1
1
10
100
1000
10000
100000
1000000
10000000
0 0.2 0.4
rho(
y)
y
Ch
TR
Co
0.00.20.40.60.81.0
0 0.1 0.2 0.3
Bφφφφ
Bz
MHD simulation: Corona (horizonatal)
- steepening + ampl. increase � shock
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.1 0.2 0.3 0.4
x
t
0.2
0.1 0.080.1
0.2
0.3
0 0.05 0.1
x
t
piston
wave
- steepening + ampl. increase � shock
- deceleration; ampl. decrease
- corona/Moreton offset
- corona/Moreton delay
t
0.00.51.01.52.02.53.03.54.04.5
0 0.1 0.2 0.3 0.4
w
t
0.2 0.10.08
piston
y = 0.012x - 0.098
0
0.1
0.2
0.3
0.4
0.5
0.6
0 20 40 60
Vm
ax/V
A
B/B0
MHD simulation: Corona (above)
streamer (current sheet)
(reconnection outflow jet)
contactsurface
“standing” shock
fast-mode
standing shock
MHD simulation: Moreton wave
1000
1200
1400
1600
1800
2000
H (
km)
H analyt (X0=1.9)H num(B0=10)H analyt (X0=3.5)H num(B0=20)
-35
-30
-25
-20
-15
-10
-5
v(k
m/s
)
V analyt (X0=1.9)V num(B0=10)V analyt (X0=3.5)V num(B0=20)
comparison with
analytical:
ρv2 w = const.;
cs = 10 km/s = const.
-35
-30
-25
-20
-15
-10
-5
00 20 40 60 80 100 120
v(k
m/s
)
t (s)
V analyt (X0=1.9)V num(B0=10)V analyt (X0=3.5)V num(B0=20)
600
800
0 20 40 60 80 100 120t (s)
-5
0100012001400160018002000
H (km)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
100012001400160018002000
X =
rho
/rho
0
H (km)
X (X0=1.9)X (X0=3.5)
Conclusion
� upward (type II burst) = driven bow/piston shock
� lateral (EUV, HeI, Hα) = temporary piston (“CME
overexpansion”)
� the time/distance of the shock formation and its
amplitude/speed depend strongly on the impulsiveness
of the pistonof the piston
� Moreton wave appears only if shock is sufficiently strong
(fast); only the upper chromosphere is affected
� downward propagating chromospheric disturbance is
quasi-longitudinal fast-mode shock that can be well
approximated by a sound shock
� Moreton wave lags behind the coronal wave due to
chromospheric inertia