High-cadence Radio Observations of an EIT Wave S. M. White and B. J. Thompson2005, ApJ, 620, L63OKAMOTO Joten/Takenori (D1)

AbstractRadio observations of the 1997 September 24 EIT waveThe radio spectrum is consistent with optically thin coronal emission.No deceleration is observed during the 4 minutes from the flare onset

EIT waveEIT stands for EUV Imaging Telescope.

In 1997, a flare-associated wave was Observed with SOHO/EIT.

Associated with -- Moreton waves in Ha -- Coronal mass ejections (CME) -- Type II radio bursts

Fe XII 195 Plasma at 1.5 MKgreen/original monochromatic/running difference

Uchida modelchromosphere Moreton wave(a shock wave depresses solar chromosphere)

corona ??? EIT wave ?(what is a coronal Moreton wave ?)In 1968, Uchida proposed fast-mode MHD shock-wavemodel to explain Moreton waves.coronamodelchromosphere

EIT wave (& the other waves)EIT waveThe wave is launched by the impulsive phase of the flareIt arises in association with CME following the flareWhat is an EIT wave?Fast-mode shock wavePropagating fronts in soft X-ray images (e.g. Narukage et al. 2002)Dark features in He I 10830A (e.g. Gilbert et al. 2004)Coronal Moreton wave or not (e.g. Thompson et al. 2000, Eto et al. 2002)Deceleration of wave front over time (e.g. Warmuth et al. 2001)

EIT wave on 1997 September 24

(Thompson et al. 2000)sharp frontflare siteSOHO/EIT2:33 UT2:49 UT3:03 UT

Moreton wave on 1997 September 24 (Thompson et al. 2000)02:45 UT02:47 UT02:49 UT02:50 UT(EIT)(Ha)(Ha)(Ha)HaEIT454750493:033:23Moreton wave: 500 km/sEIT wave: 300 km/s

Radio waveDifficult to detectTwo events reportedA radio feature moving in the same direction as an EIT wave, but not coincident with it (Aurass et al. 2002)A feature moving with a Moreton wave, but no EIT data (Warmuth et al. 2004)

Radio wave event (1999 September 24)No wave100Brightness temperature5000 K -> 1000KThe evolution is verysimilar to that seenin Ha.The exact time of EITis uncertain. (2 min)At 02:51:00 UT-> identical in position, shapeIf so, estimate EM andtemperature.

Radio waveThe radio wave speed is 835 km/s.The onset time of the flare is 02:47 UT,later than 02:43 UT made by Thompson et al. (2000)on the basis of Ha. (but, Ha: 30 s, 40 uncertainty)

Discussion 1Production of radio emissionthermal free-free emissionEmission region (spectra: 17 GHz and 34 GHz)optically thin coronal emission (flat spectrum)optically thick chromospheric emission (I ^2)Density enhancements, not temperature effectsTemperature increase -> radio flux decrease (if density is not changed)

Discussion 2The EIT wave shows no deceleration over the almost 5 minutes.

Moreton wave -> (deceleration) -> EIT wave ? All Moreton waves appear to decrease in velocity (Warmuth et al. 2004)

800 km/s in radio for up to 300 s from the flare onset: 02:49 ~02:53 UT500 km/s Moreton wave between 02:47 and 02:50 UTerror of order 3 minutes (Ha) would be needed if the radio wave is colocated with the Moreton wave.

ConclusionRadio observations of 1997 September 24 EIT wave 830 km/s (> EIT wave speed: 300 km/s)we cannot measure fast EIT-wave speed because of the short cadence: 12 minRadio wave appeared at some distance from the flare site.Since radio data are sensitive to density enhancements rather than temperature changes, the wave phenomenon observed by EIT is not a temperature effect.No deceleration is observed while it is visible in the radio images.The issue is critical since it is required to explain why EIT waves have much slower than the Moreton waves, if they are the same disturbance.