JOP138 Decimetric storms and Decametric type III bursts Received 30 January 2001. Lidia van Driel-Gesztelyi(1,2), Louise K. Harra(2), Sarah A. Matthews(2), Robert D. Bentley (2), Robert F. Willson(3), Ludwig Klein(1) (1) Observatoire de Paris, France (2) Mullard Space Science Laboratory, UCL, G.B. (3) Tufts University, Medford, U.S.A. We obtained observing time at the VLA on March 2,4,5 and 8 between 1500-1900 UT each day to study the relationship between decimetric noise storms and decametric bursts and related activity (AW 557 by Willson, van Driel-Gesztelyi, Klein and Bentley). We would like to extend the scope of the radio observations and propose coordinated observations between the VLA, Nancay Radio Observatory SOHO/MDI, EIT and CDS as well as TRACE and Yohkoh/SXT during these periods, extended to cover the observing hours at Nancay. Scientific goals: We intend to study the origin of decimetric radio noise-storms and decametric type III bursts and their relationship with phenomena in the underlying atmosphere Decametric type III bursts are a well-known form of solar activity which need not be associated with flares. Understanding their origin, i.e. the site and eventually the mechanisms where the type III emitting suprathermal electrons are accelerated, is important for two aspects: on the one hand it sheds light on the coronal evolution and on possible sites of energy conversion outside flares. On the other hand, type III bursts at decametric wavelengths seem to be closely related to the injection of low-energy electron beams into interplanetary space. Decametric type III bursts are believed to trace these same electrons closer to their source. Type III bursts, on a statistical basis, may be related to noise storms in the middle corona. Suzuki and Dulk (1985), based on observations obtained at the Culgoora and Clark Lake Radioheliographs proposed that noise storms are due to the injection of suprathermal electrons into closed magnetic structures extending to about one solar radius above the photosphere, e.g. in a streamer-like magnetic configuration, and that decametric type III bursts are generated by electron streams originating from the same source as the noise storms, but are guided along the open magnetic field lines of the same streamer configuration. While this is a plausible scenario, observational tests are lacking. Only a few imaging observations were carried out at decametric wavelengths with the Clark Lake and Culgoora arrays (Gergely and Kundu 1975; Duncan 1981), but no comparative study was undertaken with imaging at shorter wavelengths, where noise storm sources are more often detected. Furthermore, the magnetic configuration of the structures guiding the type III emitting beams was only occasionally inferred from coronagraphic observations, i.e. with a large amount of ambiguity due to projection effects. Using observations taken with the Nancay Radio Heliograph, SOHO/MDI and TRACE we have already found a good correlation between magnetic activity around a large decaying sunspot and noise storms, suggesting that the magnetic changes led to the acceleration of electrons which emit noise storms (Bentley et al, 2000). Interaction between the ``moving magnetic features'' or MMFs of mixed magnetic polarities and the moat boundary around the sunspot appeared to drive magnetic reconnection in the complex magnetic topology associated to the MMFs, which seemed to be at the origin of the observed metric noise-storms. Small jet-like EUV activity (TRACE observations) in the vicinity of minor included polarities around the same sunspot appeared to be related to type III bursts. During this observing run we want to observe a large decaying sunspot with a combination of decametric imaging with the VLA with metre and decimetre wave imaging with the Nancay Radio Heliograph and the VLA, EUV imaging of coronal structures with TRACE and SOHO/EIT and CDS, and magnetic field measurements in the underlying photosphere (SOHO/MDI) to obtain as complete a view as possible on the 3D coronal structure and the magnetic field topology at its base. Identify the source locations of the metric noise storm, compare them with those of the decametric type III bursts. To achieve this, we would like to request that SOHO/MDI, EIT and CDS as well as TRACE and Yohkoh to perform observations co-ordinated with our observing team during the following periods: March 2,4,5 and 8, 2001 between 0800-1900 UT. To be more specific, we would like to have the following observing sequences: SOHO/EIT: 171 A CME Watch SOHO/CDS: EJECT_V3 TRACE: follow the target, mainly 171 A images Yohkoh/SXT: AR tracking, if possible The VLA observations will be perfomed by Robert F. Willson, the Nancay observations by Ludwig Klein. For the coordination with the space observations Louise Harra, Sarah Matthews and Bob Bentley will be responsible. References: Bentley, R.D., Klein, K.-L., van Driel-Gesztelyi, L., Démoulin, P., Trottet, G., Tassetto, P., Marty, G. 2000, Solar Phys. 193, 227. Duncan R.A., 1981, Proc. Astron. Soc. Australia 4, 230 Gergely T., Kundu M.R., 1975, Solar Phys. 41, 163 Lin R.P. 1985, Solar Phys. 100, 537 Suzuki S., Dulk G.A., 1985, in: McLean D.J.,Labrum N.R. (eds.) Solar Radiophysics. Cambridge University Press, Cambridge, p.~289