INITIATION AND EVOLUTION
OF
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,...
Yohkoh
EIT/SoHO
MLSO
NRH
350
151 MHz
164 MHz
330
237 MHz
327 MHz
Ha/EIT
310
CME
290
F
b)
270
45
50
55
60
65
70
t (min after 09:00 UT)
75
80
Domain / Signature
in situ
Corona
- radio type II
- WL fronts, streamers
IP
(radio, WL)
Low Corona
(EUV)
Upper Chromosphere & TR
(Ha, HeI, …)
Moreton, disturbed filaments, …
timing, kinematics, intensity, spectral, morphology, …
Terminology
piston
shock
k
oc
-sh
Vsh >Vp
bo
w
Vsh >Vp
sho
ck
bla
st-
sho
ck
bow
shock
Vsh =Vp
>V
Vp <
piston
>V
Vp <
0
piston
0
projectile Vp > V
0
Large-amplitude
wave (shock)
U
0.4
0.3
0.2
0.1
0
0
1
2
3
X-X0
4
 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
depends on the amplitude!)
u
u
3
t
 (v0  2 u )
x
 0
w
u
u
w
w(t) = w0 + k u(t)
vA0
xf
x
k=4/3, w0=cs0 at b >> 1
k=3/2, w0=vA0 at b << 1
Piston Mechanism (simulations)
1D - planar
x
0.5
0.4
0.3
0.2
0.1
0
2.0
v
wave
1.5
piston
1.0
0.5
0.0
0
0.1
0.2
0.3
0
0.1
0.2
0.3
t
t
- amplitude growth + steepening  shock formation
- after t~0.15 ~const. amplitude/velocity
0.5
2D - cylindrical
x
1.4
0.4
v
0.3
0.6
dip
0.2
1
0.1
0.2
0
-0.2
0
0.1
0.2
0.3
t
0
0.1
0.2
0.3
t
- amplitude growth + steepening  shock formation
- lower amplitude, formation of rarefaction region
- after t~0.08 decreasing amplitude/velocity
Wave evolution (2D)
2.5-D MHD simulation
10000000
1000000
100000
+
Ch
10000
Bf
rho(y)
1000
TR
100
10
Co
1
0.1
0
0.2
y
0.4
1.0
0.8
0.6
0.4
0.2
0.0
Bz
By
Bf
Bz
0
0.1
b=0
0.2
0.3
MHD simulation: Corona (horizonatal)
wave
0.2
0.2
0.1
piston
0.08
0.1
0
0
w
0.3
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.1
0.2
0.2
0.1
0.3
0.4
t
0.08
piston
0
0.1
0.2
0.3
t
0.4
0.05
t
0.1
- steepening + ampl. increase  shock
- deceleration; ampl. decrease
- corona/Moreton offset
- corona/Moreton delay
Vmax/VA
x
x
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.6
0.5
0.4
0.3
0.2
0.1
0
y = 0.012x - 0.098
0
20
B/B0
40
60
MHD simulation:
Corona (above)
streamer (current sheet)
(reconnection outflow jet)
fast-mode
standing shock
contact
surface
“standing”
shock
comparison with
analytical:
v2 w = const.;
cs = 10 km/s = const.
MHD simulation:
Moreton wave
V analyt (X0=1.9)
V num(B0=10)
V analyt (X0=3.5)
V num(B0=20)
-30
v (km/s)
-25
-20
-15
2000
1600
1400
1200
-10
1000
-5
800
0
2000
1800
1600
1400
1200
600
1000
0
H (km)
4.0
X (X0=1.9)
X (X0=3.5)
40
60
t (s)
80
100
120
-25
3.0
2.5
2.0
1.5
V analyt (X0=1.9)
V num(B0=10)
V analyt (X0=3.5)
V num(B0=20)
-30
v (km/s)
X = rho/rho0
20
-35
3.5
1.0
2000
H analyt (X0=1.9)
H num(B0=10)
H analyt (X0=3.5)
H num(B0=20)
1800
H (km)
-35
-20
-15
-10
-5
1800
1600
1400
H (km)
1200
1000
0
0
20
40
60
t (s)
80
100
120
Conclusion
 upward (type II burst) = driven bow/piston shock
 lateral (EUV, HeI, Ha) = temporary piston (“CME
overexpansion”)
 the time/distance of the shock formation and its
amplitude/speed depend strongly on the impulsiveness
of 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
Thank you
for
your attention