JOP140 Origin of Type I radio noise storms Received: 12 March 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 18 (18-24 UT), 23 (17:22 UT) and 24 (20:24 UT) for a study of the relationship between Type I noise storms and related activity (AW 556 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. Scientific goals: We intend to study the origin of Type I radio noise-storms and their relationship with phenomena in the underlying atmosphere. Radio observations in the decimetre-to-meter wavelengths are the most sensitive diagnostic of supratermal electrons in the middle corona. Their most frequently observed signature come from electron populations confined in large-scale coronal loops where they radiate noise storms, consisting of broadband continuum emission with duration between ~ 1hr and several days, and bursts lasting < 1 s with much smaller bandwidth. Noise storms require persisting electron acceleration, presumably with energies ranging from a few keV to a few tens of keV, during the whole lifetime of the radio emission. Noise storms have long been known to be related especially to large spot groups, preferentially with some degree of complexity (cf. review by Elgaroy, 1977, Ch. 1.3), and with the establishment of large loop systems in the middle corona (Stewart, Brueckner and Dere, 1986; Krucker et al., 1995; references in Klein, 1998). Their onset is often related to distinct changes in the overlying corona (Kerdraon et al, 1983) and to flare-like energy release in the underlying active region (Lantos et al, 1981; Raulin et al, 1991; Raulin and Klein, 1994; Crosby et al, 1996) and their evolution is accompanied by changes of source position indicating sudden evolution of the coronal structure or of the site of electron acceleration (Malik and Mercier, 1996). This suggest that, like flares, noise storms as a signature of time-extended acceleration of electrons, are related with the discontinuous evolution of coronal magnetic fields. The energy requirements of noise stroms are probably below those of coronal heating in active regions (c.f. Klein, 1998). The question is then how the energy is converted to create the suprathermal electron populations whose radio emission we observe. Two frequently cited models rely on the interaction of newly emerging flux with the ambient corona, either in the course of magnetic reconnection (Benz and Wentzel, 1981) or through the generation of lower hybrid waves at the interface of rapidly expanding flux in the ambient corona (Spicer, Benz and Huba, 1981). The best targets to investigate the circumstances under which noise storms occur are non-flaring active regions. Conditions for discontinuous coronal evolution can also be created during the decay of the active regions - a quieter and longer-lasting evolutionary phase than the relatively short periods of flux emergence. 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. We would like to test the above result again. During this observing run we intend to observe a large decaying sunspot with a combination of 20 cm and 90 cm 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 in order to identify the source locations of the metric noise storm. 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: on March 18 between 18:00-24:00 UT, on March 23 between 17:00-22:00 UT and on March 24 between 20:00-24:00 UT. To be more specific, we would like to have the following observing sequences: SOHO/EIT: partial frame images of the target region in 171 A 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 Lidia van Driel will be responsible.