Radio Observations of the Onset of an EIT Wave Stephen White & Barbara Thompson Difficult to relate EIT waves to other phenomena due to cadence Observations with higher cadence extremely valuable Radio data (Nobeyama Radioheliograph) achieve high cadence and can see density enhancements

The EIT Wave of 1997 September 24 Classic example of an “eyebrow” event (Thompson et al., SP 193, 161, 2000), or “sharp wave” (Biesecker et al 2002) – EIT wave coincident with Moreton wave

The Flare of 1997 September 24

Optical Context for Nonthermal Emission

Nonthermal Emission: 1 second images Two flare sites: main site at trailing end of active region, also some connection to leading spot 100” away (only seen at 17 GHz); multiple sources with complicated time structure

EIT Wave: Radio Observations Radio images every 5 seconds smoothed to 30 arcsec resolution Peak brightness temperature 103-104 K at 17 GHz: bremsstrahlung from compressed coronal plasma

Radio and EUV Positions of Wave Offset likely to be due to uncertainty in the EIT clock: known to be off by up to 2 minutes. Radio data sensitive to integrated DEM, not a specific temperature.

Speed of the EIT/Radio Wave Position measured due north from main flare site: a fast EIT wave

Radio Observations of an EIT Wave “Sharp” EIT waves can be detected as radio sources in high dynamic range images (competing with nonthermal emission from accelerated electrons) Slow speeds of EIT waves vs Moreton waves likely to be a selection effect: high cadence data can see faster waves EIT waves are not temperature effects In this event, EIT wave onset appears to be at the onset of the impulsive phase – cf CME result EIT wave does not become visible until it has propagated some distance from the flare site: needs to sweep up material?