SOHO Joint Observing Programme 059 EXAMINATION OF STRUCTURE AND TEMPORAL VARIATION OF CORONAL LOOPS Authors:Robert Walsh and Jack Ireland(St Andrews), Richard Harrison (CDS), Barbara Thompson (EIT), Julia Saba (MDI), Phillipe Lemaire (SUMER), Sarah Matthews (Yohkoh) E-mail Addresses: robert@dcs.st-and.ac.uk,jack@dcs.st-and.ac.uk, harrison@solg2.bhnsc.rl.ac.uk, thompson@eitv3.nascom.nasa.gov, lemaire@sumop1.nascom.nasa.gov, jsaba@solar.stanford.edu, sam@msslac.mssl.ucl.ac.uk Progress: First Draft February 4, 1997 Objective: Our aim is to obtain temperature, density and magnetic field structure and to investigate high cadence temporal variations within the target coronal loop system. Conditions Necessary to Run: Occurrence of a suitably well defined coronal loop system (on either the disk or limb) and involvement of at minimum CDS. Scientific Case: The solar corona is not homogenous and uniform but is a complex and dynamic environment consisting of a large variety of loop structures. These loops are thought to outline the magnetic fieldlines present in the solar atmosphere. Our aim is to describe as fully as possible, the spatial and temporal structuring of temperature, density and magnetic field in typical loop systems. In the first portion of the study (Sub-JOP1), the loop system is treated as a static object, allowing long exposures over a large area to obtain detailed structural information on the temperatures, densities and magnetic fields present. In the second portion (Sub-JOP2, Sub-JOP3) of the study, we use long duration, high cadence CDS observations at specific points in the loop system (for example, over a suspected loop footpoint and/or apex). This is designed to look for evidence of short timescale heating events associated with loop systems - for instance, wave activity, microflares and small scale reconnection events. Thus, the density and temperature diagnostics from CDS are essential, as are coincident MDI magnetograms. SXT will provide coverage in higher temperature lines. EIT will provide information on any significant events that occur exterior to the CDS field of view (for example, a prominence eruption). Basic Method: A pilot study for this JOP was run as the St.Andrews/RAL LOOPS Campaign in mid-November 1996. The JOP should be run as a target of opportunity programme - i.e. listed for a period of about 4 weeks. We should anticipate a minimum of three runs of about 5-10 hours each. This JOP is split into three 'sub-JOP' campaigns, which together form a thorough examination of coronal loops. These are: - Sub-JOP1 - Structure of Loops - Sub-JOP2 - Slow Variations in Loops - Sub-JOP3 - Fast Variations in Loops For each run of the JOP either one sub-JOP or a selection of the sub-JOPs will be used - dependent on the target and the choice of the JOP leaders. The instrumental support for each sub-JOP is given below. As an example, sub-JOP1 may be run on a loop system to provide a large image of a region, to be followed by a run of sub-JOP3 to look at fast variations within one of the loops seen in the sub-JOP1 image. Durations: Sub-JOP1 - 2N hours, where N is the number of runs of CDS' LARGEBP2 Study. Would be nice to have N larger than 1! Sub-JOP2 - A minimum run of 2 hours but strongly recommend much more. Sub-JOP3 - A minimum run of 2 hours but strongly recommend much more. Pointing and Target Selection: Both disk and limb target loop systems will be considered where apparent loop structure is well-defined in CDS, EIT and SXT images. For sub-JOP2 and 3, different positions within the target loop system itself may be appropriate. This will be at the discretion of the JOP leaders.For example, within one run,the CDS slit could be placed on the apex of the loops and then at the footpoint areas. MDI magnetograms will be of immense help in slit positioning assuming that for a simple on-disk bipolar target, the loop apex lies between the areas of opposite polarity while the footpoints are essentially the areas of strong magnetic field. On disk targets would involve all the instruments as indicted below. It would be nice to select region within the MDI high resolution field. Limb targets would be studied using CDS, EIT and SXT only. Operating Details: (i) CDS - Studies to be run for each sub-JOP: Sub-JOP1: LARGEBP2 (CDS Study 10, Variations 25 or 26) NIS, 2x240 slit, 240x240 area, 120 locations Exposure 45s (Var 25) or 20s (Var 26 - if very bright!) Duration 6949s (Var 25) or 6579s (Var 26). Lines: He I 584, O III 599, O V 629, Ca X 557, Mg IX 368, Mg X 625, Si X 346, 356, Fe XII 364, Fe XIII 348, Fe XIV 333, Fe XVI 360, Si XII 520, backgrnd 355, 335. Sub-JOP2: Run EJECT_V3 once followed by a series of LOOPS_2 and a final EJECT_V3. Total duration should be several hours - the longer the better. EJECT_V3 (CDS Study 11, Variation 18) NIS, 4x240 slit, 240x240 area, 60 locations, Exposure 10s, Duration 991s. Lines: He I 584, O V 629, Si X 347, 356, Mg IX 368, Fe XVI 360. LOOPS_2 (CDS Study 12, Variation 7) NIS, 2x240 slit, 10x240 area, 5 locations Exposure 20s. Duration 134 per raster. Lines: He I 584, O V 629, Mg IX 368, Fe XVI 360. Sub-JOP3: Run EJECT_V3 once followed by a series of LOOPS_3 and a final EJECT_V3. Total duration should be several hours - the longer the better. EJECT_V3 - see above. LOOPS_3 (CDS Study 123, Variation 1) NIS, 4x240 slit, 4x120 area, 1 location Exposure 10s - 50 rasters. Duration 707s. Lines: He I 584, O V 639, Mg IX 368, Fe XVI 360. (ii) EIT - Ensure that there are full-Sun images in Fe IX/X, Fe XII within the CDS Study timeframe. Alternatively, select a region centred on CDS' pointing and produce 'fast' images in Fe IX/X and/or Fe XII. Ensure in both cases that there is a He II image near in time for alignment with CDS He I. (iii) MDI - Ensure magnetogram coverage during operation. High resolution images (i.e. high time resolution coverage or/and high spatial resolution) preferable if possible. (iv) SUMER - Sub-JOP1: No participation. Sub-JOP2 and 3: If CDS target loop is passing SUMER field, then run single location exposures with high temporal resolution should be performed over loop. Suitable lines would include at least one also seen by CDS for co-registration and one or two at transition region temperatures and above. (v) Yohkoh (SXT) - Ensure at a minimum SXT synoptic observations during JOP and, if possible, home in on selected region for higher cadence observation.