INITIATION EVOLUTION CORONAL SHOCK WAVESoh.geof.unizg.hr/SOLSTEL/images/dissemination/conferences/oral/2… · INITIATION AND EVOLUTION OF CORONAL SHOCK WAVES ... EUV, SXR, HeI, coronograph,

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

Wave evolution (2D)

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

Thank you

for for

your attention