JOP146 Fine Temperature and Density Structure of Coronal Loops in a Bipolar Active Region Authors: J. Cirtain; C. Kankelborg, P. Martens Objective: Observe coronal loops on the west limb with multiple instruments. These loop(s) must originate from one bipolar region or a region of minimum magnetic complexity. Necessary conditions for Operation: A relatively simple region consisting of a bipolar surface origin is requisite for co-operation of all instruments. Scientific Justification: Currently, several diagnostic approaches for the determination of the temperature stratification along loops exist, dependent upon the observing instrument. These determinations give widely differing results for the nature of the plasma within a coronal loop. Aschwanden et al (ApJ 550,1036; ApJ, 550,1059; etc.) has shown in multiple papers the nearly isothermal results obtained through filter ratios derived from EIT and TRACE data. J. Schmelz and others (ApJ, 556,896) have produced multi-thermal results through the analysis of spectra obtained from CDS observations while Acton and Priest (ApJ, 539,1002) have developed a uniform heating model from SXT data. These separate studies have shown that results vary depending on the instrument and subsequent method of analysis. It is therefore of great necessity to perform a co-operative study with all these instruments further constraining the actual thermal gradient of coronal loops. There have been many joint observing programs with similar goals. However, these have yet to provide a data set that both has a minimum of magnetic complexity, required to distinguish a unique structure by the CDS spectrograph, and co-observation by SXT, TRACE, CDS and EIT of a simple structure on the limb. Recently, JOP 145 was run with SCT< CDS, TRACE and EIT. This JOP offered all of the necessary criteria for the study except it changed target before the structure made it to the west limb. Unfortunately, there are many data sets but none offer that which is here stipulated as necessary to accomplish the scientific study suggested. J. Schmelz has developed a Differential Emission Measure technique applied to spectral intensity numbers from CDS observations. This method can be modified to evaluate both the spectra from CDS and the filter output from TRACE and SXT. By comparing the spectral intensities from CDS with the 171 A, 195 A, and 284 A filters from TRACE and the AlMg and Al filters from SXT, a high resolution composite of the loop can be created that has spectral data for the structure to further constrain the actual nature of the plasma in both temperature stratification along the loop and fine structure detail of the loop. This analysis method may provide the unique ability to determine the real temperatures of plasma within these structures as well as perform a diagnostic cross calibration of the three instruments. Pointing: This program is to be executed at the solar limb thereby minimizing projection effects and preferably targeting a region that has been under observation as it rotates across the disk. Operation Details: The JOP is to be performed in the following manner on a per instrument basis: CDS: target of opportunity with as many sequences as possible. TRACE: observations to overlap with other instruments when target approaches west limb. Previous observations as loop rotates across disk are preferred. SXT: target of opportunity only with regard to the PFI images. The entire study will be on a target of opportunity basis for the month of September or as instrument schedules dictate. CDS: Three sequences to be run: O_LOOP1 and O_LOOP2. O_LOOP1 creates a 160 x 240 arc second raster in six wavelength bands. These bands are He 1 584.33 A, O III 599.66 A, O V 629.73 A, Ne XI 562 A, Mg IX 368.06 A and Fe XVI 360.76 A. It steps in 4 arc second increments. The exposure time at each position is 10 seconds resulting in a cadence of about ten minutes. This should be the initial program for the CDS observation. O_LOOP2 has an almost identical raster but it creates a raster with thirteen wavelength bands over approximately forty minutes. The wavelengths for this program include the six wavelengths for the O_LOOP1 run with the addition of Si XII 520.665 A, Si X 347.40 A, Al XI 562.77 A, Fe XIV 353.92 A, Si IX 345.220 A, Si X 356.0 A and Mg X 624.817 A. This sequence is intended to supplement the O_LOOP1 program and should only be run after the O_LOOP1 program has completed several runs. These sequences must be run simultaneously with TRACE and SXT. Multiple runs sequentially are preferred. TRACE: Through the use of currently available observing programs, specifically mostly171.utim and mostly195.utim, coverage of an active region will be possible in 171A, 195A and 284A. These filters correspond to spectral lines available with CDS and provide approximate temperatures that overlap the temperatures available in CDS and SXT. Also intermittent C IV 1550 A. runs would be required to supplement the temperature analysis method to be subsequently employed. The .utims that are suggested for use in this study offer a sustainable cadence of around 40 seconds. The mostly171.utim offers the 171 filter for the main wavelength with 195, 284, 1550, 1700 and WL every eight cycles. The mostly195.utim functions the same way but has 171 in context instead of 195. EIT: Cadence to be determined as allowed by the operations team. Partial frame images would significantly increase the cross calibration ability of the observer, especially in 171A, 195A and 284A. However, full disk observations in 171 or 195 would be beneficial for co-alignment. SXT: This instrument uniquely provides the higher temperature analysis of these structures. The standard FFI table would be appropriate. If the active region is not so active as to overexpose the CCD on SXT a PFI table could be developed that would visit the limb and briefly point at an appropriate target. This could be accomplished by using the multi-OR capability of SXT. If the loop region is large a 128x128 OR at full-resolution will be sufficient. This should use sequential exposures in Al.1, AlMg, and Al12 with automatic exposure control. If the multi_OR is required the region must be observed long enough for the AEC to settle. PFI images could follow the same basic procedure with a 64x64 OR at full resolution. It is important to note that although the structure may not be visible in the SXT images, this to is an important null result.