EIT/CDS/SUMER Loop Fine Structure Observing Program G. Peres, R. Rosner, A. Poland, Purpose: To observe isolated loop structures in coronal holes or on the limb with SUMER, CDS and EIT to determine temperature and density both along and across the loop structure (i.e. along and across the dominating magneting field), as well as the velocity field, as a function of time. Observations made with SOHO coronal instruments have clearly shown the presence of isolated loops in coronal (polar and non-polar) coronal holes. Since they are isolated there is virtually no risk of confusion with other nearby loops and no risk of superimposing plasma along the same line of sight but from different loops. Therefore such loops offer a unique opportunity to observe and analyze the physics of loops, believed to be the building block of the confined corona. An important aspect of this program is to observe in the light of many emission lines simultaneously so as to study the coronal plasma conditions over a wide range of temperatures, from chromospheric to coronal ones. This feature, among other things, allows to determine whether any difference in morphology seen in the light of the various lines, as well as time variability, is due to density or temperature effects. This observing program will help determining if the velocity flows predicted by extant siphon flow or, alternatively, microflaring loop models occur in real loops. The capability of SUMER to achieve sub-arcsec angular resolution along with very fine spectral resolution will help to study the fine structure and, in particular, how plasma conditions change across the loop structure. Therefore it is important to target loops observable with such an instrument. Observing Program: 1. In EIT: Use synoptic observations to identify promising loops, e.g. the ones isolated and evident against a dark background, for instance inside coronal holes or at the limb. Once the observing program begins, EIT takes small images of the loops at the fastest cadence possible in all four bands. 2. In SUMER: if the loop fall in a place of the solar disk accessible to SUMER move the slit on it and use the 0.3"x120" slit, The line selection should cover a range from the chromosphere to the corona. Here we propose the following (redundant) list, arranged in order of increasing temperature of most efficient formation: C III 1335, C III 1175.7, C III 977.02, N III 989/991, S V 796, N IV 765.14, N V 1238, O V 629.73, O V 1218, O VI 1032/1037, N VII 770, Ne VII 895, Si VIII 1475, Mg X 625, S X 1213, S X 1196, Fe XII 1242, Si XII 520. The selection as well as the exposure times should comply with the requirements by SUMER, which may demand last minute selection. Such an aspect is particularly true for lines too bright or which fall in the wings of Ly_a. 3. In CDS: Use the 2x240" slit, and cover an area 2'x4', make 100 sec of individual exposures for a total duration of 1h 30m. If the loop is too large to fit into a single exposure, move the image so the field of view is just above or just on the side of the previous one so as to cover the entire loop, and make another image, and so on until the entire loop is covered. Most loops, however, should be covered with a single image. This will give us a good overall view of the loop over a wide temperature range. Use the following lines in CDS: He I 584, He II (2nd) 607., O III 599.59, O IV 554, O V 629, Ne VI 562, Ca X 557, Mg IX 368, Mg X 624, Fe XII 364, Si IX 342/349, Si X 347.5/356, Fe XIV 334.2/353.8, Si XII 520 ---- Coordination with the other instruments on SOHO: UVCS - nearby outer coronal observations would be very useful if large coronal loops are studied at the solar limb. Observations in the O VI channel, in particular would allow to expand in the higher corona the O VI observations made on disk.