Coronal IP ShocksNat Gopalswamy NASA/GSFC

Elmau CME Workshop, 2003 February 7 Plenary talk

Sun

Earth

Plan of the talk

• Type II bursts & CMEs• Type II bursts, SEPs &

CMEs• Metric & IP type II bursts

Wind/WAVES & SOHO/LASCO Data

IP: 15 MHz – 20 kHz (3Ro – 1 AU); 15-1MHz DH

Type II Radio Bursts• Discovered by Payne-Scott et al. (1947) at metric

wavelengths (<150 MHz). - Malitson et al. (1973) in the IP medium using spaceborne

radio instruments(see reviews by Cane, Reiner, Gopalswamy in AGU monograph 119)

• Plasma Emission Process is responsible:- [ Fast CMEs drive] MHD shocks- Shock accelerates electrons (~10 keV)- Nonthermal electrons generate Langmuir waves at local

plasma frequency (fp)- Langmuir waves scatter off of ions or combine to produce

radio emission at fp (fundamental) and 2fp (harmonic)

Radio Sky

Interplanetary(bounded by Red lines)

coronal

Nelson & Labrum, 1985)

LASCO CME DH Type II

Type II

SA Event (Type III Bursts)

F

H

CME-driven metric & DH type II

An IP Type II & its CME

Type II

f = 3MHz n = 2.8x104 cm-3

(harmonic emission)

Type II bursts track the CME through the IP medium

Type III

DH Type II burst starts when the CME reaches ~ 2 Ro

• The RAD2 spectral range (14-1 MHz) Wind/WAVES correspond to 2-10 Ro Type II bursts can identify shock-driving CMEs in the near-Sun IP medium.

• Too much delay: due to accelerating CMEs

• CME delay: Disk events

All, FW &DH CMEs

• > 5000 CMEs during 1996-2000• ~150 Fast & Wide (FW) CMEs• ~150 DH Type II bursts• ~ 50 FW frontside western

CMEs• ~ 50 Major SEP events• 1-3% of all CMEs are

important for SEPs• Electron accelerators are also

ion accelerators

• DH type IIs, fast and wide CMEs and major SEP events: similar solar-cycle variation.

• Close correlation implies physical relationship: the same CME-driven shock accelerates electrons that produce DH type II bursts, and SEPs.

• The number of DH type II bursts is the largest because eastern events are also included.

• Minor differences due to other parameters like Alfven speed.

Solar Cycle Variation of Energetic Events

Speeds of CMEs associated with Metric & DH type IIs

Average CME speeds increase in this order:

. General population (G)

. Metric type II related (M)

. DH type II related (D)

Similar tendency for widthand acceleration of CMEs

D

M

G

Lara et al. 2003, GRL, in press

Since DH type II bursts are 100% associated with CMEs, these propertiessuggest that metric type IIs are also due to CMEs, but less energetic

Two Shocks from the same source?

• “Alfven-speed hump” expected based on B, n profiles in the quiet corona (Hollweg, 1978; Krogulec et al, 1994; Mann et al. 1999)

• Include active region: 3 regions of interest (Gopalswamy et al. 2001)

• Easy to drive shocks on either side of the “Alfven-speed hump” Gopalswamy et al. JGR (2001).

• Easier to shock the corona in the transverse direction? (Gopalswamy, Kaiser & Pick, 2000).

• Type IIs occurring to the right of the hump are likely to be strong and indicative of IP shocks.

Metric domain

fp

Example of the metric – DH type II (02/12/22)

Hiraiso – metric type II

WAVES type II

The CME propagatesthru a tenuous medium where Va is expected to be high

Summary• Any short-lived driver with ~ 350 km/s may drive a shock close to

the Sun, but not beyond.• Blast wave: 1. Speed declines with time, 2. Weakens further at the

Alfven speed hump. (No blast waves observed in situ; “driver-less” shocks are due to limb CMEs!)

• CME-driven: 1. CMEs accelerate low in the corona.2. Depending on CME speed and initial height, CME can drive shocks

in the corona & IP medium (cause metric & IP type II)3. CME can drive a shock in the metric corona, lose it around Va peak

and drive again in the IP medium. If it does not drive again (CMEs of moderate speed), situation similar to blast wave.

4. Solar wind works against shock-driving capacity of CMEs in the IP medium

5. SEP release height (Kahler et al., 1994) coincides with Va peak