complete characterization of a cme-driven shock from uv, white light and radio data

““IAGA2”, Cairo – 05/12/09IAGA2”, Cairo – 05/12/09

““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso

Complete characterization of a Complete characterization of a CME-driven shock from UV, white CME-driven shock from UV, white

light and radio datalight and radio data

Complete characterization of a Complete characterization of a CME-driven shock from UV, white CME-driven shock from UV, white

light and radio datalight and radio data

Alessandro Bemporad

& Salvatore MancusoINAF – Turin Astronomical Observatory

Alessandro Bemporad

& Salvatore MancusoINAF – Turin Astronomical Observatory



Outline

• Introduction

• The March 22, 2002 CME

• Shock front: radio, white light and EUV signatures

• Estimate of up-stream plasma parameters

• Rankine-Hugoniot equations for oblique shock: estimate of down-stream plasma parameters

• Conclusions


““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso Coronal Mass Ejections

observed by UVCSCoronal Mass Ejections are sporadic events where 1015-1016g of mass are launched into the Interplanetary Space at velocities ranging between ~ 500-2000 km/s.

ee

epe n

m

neff

2

Fast CMEs drive fastfast shocksshocks that accelerate SEPs and electron beams (~10 keV) able to generate plasma wavesplasma waves at the local plasma frequency fpe that scatter off ions or combine to produce

type II radio emissiontype II radio emission at fpe (fundamental) and 2fpe (harmonic).

Metric type II radio bursts offer clear evidence of coronal shocks but: 1) no spatial resolution: direct imaging of coro-nal shocks remains in fact an outstanding observational challenge; 2) no direct information on physical properties of shocked plasma.

Over the last 14 years observations of coronal shocks by the

UV Coronagraph Spectrometer (UVCS) on SOHO provided

both spatial resolution and unique diagnostics for the physical

processes in coronal shocks.

arc

sec

time

2fpe

freq

uen

cy

fpe



The passage of a shock heats the emitting material and is detected as broad wings mainly in the non neutral ions. In the UVCS spectra the presence of a shock front is more likely dete-cted in the brightest spectral lines such as the O VI doublet and the H I Ly-line, providing a direct diagnostic of the kinetic temperatures behind the shock.

Detections of shocks in UV spectra have already been reported for four CMEs (Raymond et al. 2000; Mancuso et al. 2002; Raouafi et al. 2004; Ciaravella et al. 2005; Mancuso & Avetta 2008).

Broad wings in the O VI doublet (right) as results of a shock passage (left; from Mancuso et al. 2000, A&A ).

CME-driven shocks as seen in UV spectra

shockfront

None of these works made a determination of pre- andpost-shock physical parameters of plasma


““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso The March 22, 2002 event

• CME start time ~ 10:30 UT• Fast CME (vLASCO cat = 1750 km/s)• Associated to: - X-class flare - Strong radio burst• UVCS observationsFOV: slit centered at 4.1 Rʘ, lat = 70°SWTime coverage: 00:55 – 18:29, 200s exposures

11:06 11:30 11:54

LASCO/C2 images

UVCS slit

coronalstreamer


““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso Shock signature in Radio data

Nancay Radioheliograph – 164 MHz

CME source AR

CME

A few minutes after the CME start time a strong arch-shaped radio emission (164 MHz) appears above the limb. The radio emission is located just above the region where the plasma has been evacuated. At the same time interval a type-II signature has been detected from the Potsdam radiospectrometer

EIT 195

22/03/2002, 10:40 UT

→ possible early signature of the CME driven shock.

In the following minutes a type-II radio burst is detected by the WIND spacecraft. As the shock expands, the streamer plasma density decreases with altitude, leading to the observed frequency drift with time.

→ signature of the CME-driven shock


““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso Shock signature in white light

LASCO/C2 base difference images

Shock front

Shock front

Shock front

2002/03/22, 11:06 2002/03/22, 11:30 2002/03/22, 11:54

CoronalstreamerUVCS

slit



Ly 1215Å intensity O VI 1032Å intensity

Shock signature inUVCS spectra

Ly 1215Å: due to radiative excitation alone. Post-shock plasma accelerated & heated → Ly emission decreases (Doppler dimm.)

O VI 1032Å: due to both radiative and collisional excitations.Post-shock plasma compressed and accelerated → OVI radiative component Doppler dimmed, collisional component increased.

11:30

Shock front

Pre-shock coronalstreamer

Shock front

Pre-shock coronalstreamer

Streamer deflection Streamer deflection

Polar angle (°) Polar angle (°)

Tim

e (h

) →

Tim

e (h

) →



Line of sight

post-shock

pre-shock

O VI 1037.6

O VI 1031.9

UVCS O VI line profiles Post-shock plasma:

• Tk ~2 times larger than bgd corona• Tk fades back to

coronal values in ~3h

These are only upper limits to the real Tk:obs. broadening = heating + LOS exp.

• vLOS ~ 120 km/s• vLOS fades in ~3h

Taking into account the shock velocity on the plane of the sky:

• vPOS ~ 1150 km/s• CME ~ 6° toward the observer, mainly on the plane of the skyplane of the sky

backgroundcorona



1

32

These equations have in general up to 3 possible solutions for the compression ratio r = d /u. If we stay in the region of the plane [(vu),(Bu)] where rr the has a unique solution:

1

MHD-Rankine-Hugoniot equations for oblique shock

0

0

012

1

0/

02/

0

0

2

0

022

x

xyyx

x

xyyxy

yxyx

yx

B

BvBv

v

BvBvBpv

BBvv

Bpv

v

Mass fluxX-momentum

Y-momentum

Energy

Maxwell’s eq.

Maxwell’s eq.

r

vnT

vuBu

uuu

,,

,,,

vdBdd

ddu

v

BTB

,,

,,,Rankine-Hugoniot eq.

vuBuu

uuu

v

BnT

,,

,,,

vdBdd

ddd

v

BnT

,,

,,,Rankine-Hugoniot eq.

?

Estimate of Upstream parameters1) Derive TTuu, n, nuu, v, vuu from UVCS data;2) Derive r, r, vuvu from LASCO;3) Assume a value for BuBu

Downstreamparameters



Ly 1215Å intensity

Polar angle (°)

Tim

e (h

) →

Upstream parametersfrom UVCS data

• Assume ne(r), Te(r), vout(r) profiles along the LOS (Cranmer 1999)• Vary densities and temperatures by introducing two costant multiplier (Kn and KT for density and temperature, respectively);• Compute the expected I(Ly) and I(OVI) by iterating over all the possible values of (Kn, KT) pairs and integrating along the LOS;• Find the (Kn, KT) pair that better reproduces the observed intensities.

Results: (Kn, KT) = (4.3, 0.37) → nnuu(POS)(POS) ~ 9×104 cm-3

TTuu(POS)(POS) ~ 2×105 K

Tim

e (h

) →

vshock = 1150 km/s

Shock frontI(Ly)u = 9.2 x108 phot cm-2s-1sr-1

(interplanetary Ly- subtracted)

I(O VI)u = 7.6 x106 phot cm-2s-1sr-1

upstreamplasma

downstreamplasma


““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso Upstream parameters

from LASCO/C2 data

• Measure the pre- and post-shock WL• Assume a thickness L along the LOS for the involved coronal region → L = 0.53 R๏ (sherical shell: thickness d=104km, r=2.5 R๏)• Given L, estimate the fraction k• Estimate the compression ratio rr as

KA

KABr

)1( Result: r r ~ ~ 2.82.8

X (R๏) X (R๏)

Y (

R๏)

Y (

R๏)

vshock

vwind

radial to the Sun

shock front

UVCS slit

R-H equations hold in the frame of reference at rest with the shock front

vshock= 1150 km/s

vwind~300 km/s

vvuu ~~ 1080 km/s 1080 km/s

vuvu~ 15°~ 15°

Bu ║vwind

BuBu~ 70°~ 70°

11:30

L

pre-shockwhite light

LOS

LOS

post-shockwhite light

Compressedplasma

A =

B =

Fraction k

kA =B-A =


““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso Downstream parameters

8.2

15

70

/1080

109

10234

5

r

skmv

cmn

KT

vu

Bu

u

u

u

0.38

0.74

/475

063.0

1046.1

051.07

vd

Bd

d

d

d

u

skmv

GB

KT

GB

Rankine-Hugoniot eq.

(pre) = 0.027 → << 1(post) = 3.52 → > 1

vA(pre) ~ 350 km/s > vwind(pre) → sub alfvènic flow (MMAuAu = 0.85 = 0.85)vA(post) ~ 260 km/s << vwind(post) → super-alfvènic flow (MMAdAd = 2.94 = 2.94)

vshockBu

Bu=70°

Bd=74.0°

Bd

vwind(pre)

vu=70°

vwind(post)

vd=22.4°

vshock

These results hold in the reference frame at rest with the shock surface. Hence, in the referenceframe at rest with respect to the Sun:

vwind(pre) ~ 300 km/s vwind(post) ~ 770 km/s



Summary

• On March 22, 2002 a fast CME occurred, related to X-class flare and type-II radio burst.

• It is possible to identify the transit of the shock front both in the LASCO/C2 and UVCS data.

• From these data we derived an estimate for the upstream plasma parameters, but the magnetic field.

• Given the upstream parameters and the compression ratio r from LASCO data, the R-H equations give the downstream parameters.

• Results: the shock transit corresponds to 1) plasma compression (~2.8), 2) heating (by a factor ~70) and 3) transition from sub- to super-alfvenic flow and 4) from <<1 to >1.



LASCO/C2 wavelet enhanced images

Shock front

Shock front

Shock front

Coronalstreamer

Shock signature in white light



Bemporad & Mancuso (2009)

Magnetic field estimate


““Characterization of a CME-driven shock from UV, Characterization of a CME-driven shock from UV, white light and radio datawhite light and radio data ” – Bemporad & Mancuso” – Bemporad & Mancuso UVCS O VI line profiles

Post-shock profiles are:

• broader than coro-nal profiles (broade-ning fades with time)

• red-shifted (shifting fades with time)

Normalized coronal pre-shock profiles

Normalized post-shock profiles (coronal profile sutracted)



Ciaravella et al. (2005)

Raymond et al. (2000)

Mancuso et al. (2002)

SEP ?

East Limb NO SEP

West Limb SEP

Coronal shocks Coronal shocks detected by detected by UVCS/SOHOUVCS/SOHO

Proxy for SEPsWE



When the shock arrives at the UVCS slit

- H I Lyman alpha intensity drops down

- O VI lines develop broad wings

- Si XII line intensities increase.

June 11, 1998June 11, 1998 (Raymond et al. 2000)(Raymond et al. 2000)



June 28, 2000June 28, 2000 (Ciaravella et al. 2005) (Ciaravella et al. 2005) O VI 1032

18:59 UT

19:05 UT

19:02 UT

O VI 1037



A compression ratio of 1.8 was the only value consistent with both O VI and H I line widths

March 3, 2000March 3, 2000 (Mancuso et al. 2002)(Mancuso et al. 2002)

O VI 1032, 1037

t = 02:21 UT t = 02:24 UT

complete characterization of a cme-driven shock from uv, white light and radio data

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