Submitted by: Barbara Bromage (b.j.i.bromage@uclan.ac.uk) SOHO Joint Operations Programme 102 STRUCTURE OF CORONAL HOLES WITH PLUMES DRAFT 2: 15 April 1999 AUTHORS: Barbara Bromage(CDS) and Giulio Del Zanna(CDS); Craig DeForest(MDI); Philippe Lemaire(SUMER) IN BRIEF: uses CDS to determine angle with radial of the expansion of coronal hole boundary (polar and low-latitude holes); high-time resolution study of low-latitude plume (with GIS); spectroscopic diagnostics of coronal hole, plume and quiet sun boundary; comparison with chromospheric network; comparison with cell-centre 'periodicities' in TRACE/optical data. BACKGROUND A coronal hole is a region of open field. The open field emerges from the chromospheric network structure and opens out above the chromosphere, to maintain pressure equilibrium horizontally. The angle the field lines make with the radial direction depends largely on the angle that the last open field line at the boundary makes with the radial and on the size of the hole. Plumes are believed to lie parallel to the open field lines and hence are seen to emerge in the lower corona at super-radial angles. It is not at this time clear whether the plumes form in magnetic field originating within the network or adjacent to it (or both). In this study we examine and compare these structures (boundary, network, plumes) which make up the coronal hole, to attempt to resolve some of the questions concerning coronal hole structure. Quasi-periodicity in the intensity of plumes has been observed, in EIT data and in CDS data (in one observation). Here we attempt to locate a low-latitude plume on the disc (using a spectroscopic technique) and then study its variability at high time resolution, over a longer time than previously (with CDS). Simultaneous observations with MDI, TRACE and an optical observatory will be used to look for any relationship between plume and chromospheric variability. The base of the plume will be located relative to the network using chromospheric lines and MDI high-res data. OBSERVATIONS With CDS - 4-6 hours NI study on boundary of polar hole at the meridian, any convenient time in the week. - on a low-latitude hole, 4-6 hours NI study, 2 days before meridian crossing and again 2 days after. - on the same hole as it crosses the meridian, begin with 1 hour NI study to locate a plume, followed by about 6 hours NI study on the boundary/hole, and then, when the quick-look data has revealed a plume: 9 hours GI scan across the plume. The NI studies will be selected from UCLAN_N2, UCLAN_N3 and UCLAN_N4; the GIS study is HTGIWE. The series of observations should be accompanied by a short sequence of studies for calibration purposes - 2 hours (total) alternating GI and NI short studies (ARC_CALN and DEM_GIS). (Total CDS run-time for all studies in the JOP about 32 hours.) MDI - high rate observations during study of plume. TRACE - high-time-res studies using chromospheric line ( plus coronal line, preferably just below 10**6 K). SUMER - observations of network (as in JOP22) and plumes (Ne VIII) for doppler shift. EIT - as available. Optical CaII observations at high time resolution will be obtained if available.