Cool loops, transequatorial loops and coronal waves

An MSSL compilation (Louise Harra, Sarah Matthews, Lidia van Driel-Gesztelyi) with help (Cristina Mandrini, Alphonse Sterling)

Cool loops in active regions

• First seen with Skylab, routinely observed by CDS• Temperature range 2x104 – 106 K• Both complete and partial loops are seen• Contrast generally high and behaviour is dynamic (e.g.

Kjeldseth-Moe & Brekke, 1998, Harra-Murnion et al., 1999)• Conflicting reports about the relationship between hot and

cool plasma Are they cooling /structures? Heating? What is the role of

e.g. siphon flows

Observations

• 3 AR on the limb were studied with CDS, SXT and MDI• O v and SXT intensity revealed variability (EJECT_V3)• O v velocities show flows• MDI data was used to determine magnetic field direction Parallel/anti-parallel flows in both legs => siphon flows Oppositely directed flows in each leg => heating or cooling

Flare 1 ~ 18:30Flare 2 ~ 22:30

O v with SXT contours O v with SXT contours

Magnetic field model for interconnectingloop on 23 Feb 98. Arrow shows direction of B.

Velocity maps in O v. Contours – SXT data. Black – red-shifted,White – blue-shifted.

Conclusions

• Complete cool loops are hard to find!• Two main types of TR emission in ARs:

– Bright footpoints: seen at the flare site– Cooling loops: occur when a small flare occurs and can

either be contained within the AR or linking them

Transequatorial loops

• Important component of the Babcock model – clues to the dynamo

• CME association (e.g. Khan & Hudson, 2000, Glover et al. 2003)

• Predicted to be formed by reconnection

Reconnection?

• We saw an increase in intensity along with a cusp feature in SXR with (apparently) open field lines visible in EUV followed be a CME – consistent with the ‘standard’ LDE scenario.

• First observation of a TEL at < 1 MK, velocities show mostly downflows (cooling).

Properties of coronal waves

• From a study of 21 waves, 19 were associated with type II radio emission (Klassen et al., 2000).

• Seen in the EUV and soft X-ray • Typical speed ~200-350 km/s (EUV), 600km/s (SXR).• Frequently associated with flares.• Often associated with CMEs (Biesecker et al., 2002).• Bright front followed by a large region of dimming.

13:28 14:00 14:12

14:21 14:35 14:53

• Fast mode shock wave related to a flare (e.g Uchida’s work)?• Shock wave caused by a fast CME?• Opening of field lines related to a CME (e.g. Delannee and

Aulanier)?

☼ Synoptic CDS observation observed the dark region behind a wave front. Blue shifted velocities were observed (Harra & Sterling, 2001)

First Spectroscopic Observation of DimmingFirst Spectroscopic Observation of Dimming

TRACE difference images

Two wave fronts are seen

No motion from either wave front is seen in CDSThe dimming region does not enter the CDS FOV!Filament eruption seen

Filament eruption associated with wave

This figure shows images at a 300 km/s blue shift. This

feature is not obvious in the images alone.

O v difference

Low v component High v component

Explanation?• Chen et al. (2002) carried out 2D

simulation of a piston-driven shock.

• Our bright wave front could be their ‘EIT wave front’.

• Our dimming region the density rareified region with strong expansion velocities.

• They suggest that the ‘EIT’ wave result from opening of field lines associated with a filament eruption.