JOP-039 Polar Plumes ==================== "Sketch" plan: Compiled-by: Craig DeForest (MDI) 29-Feb-96 Updated: 4-Mar-96 Summary: We plan to track emission from each of several polar plumes, using each of six SoHO instruments during an eight-hour spacecraft off-point. The off-pointing activity is designed to bring MDI's high resolution field of view to the South coronal hole, which is currently canted at a favorable B angle. Steady-state plume behavior is interesting at high altitudes > 1.5 RO, where plumes are observed to be relatively quiescent structures, and where previous models show that the bulk of the acceleration happens. Lower down, non-thermal spectral broadening and time variation are more interesting. It is anticipated that some plume footpoint brightening events will be seen, and that their causes (presmably magnetic recombination) and effects (presumably plume heating and density enhancement, possibly with visible ejecta) can be tracked through the several instruments' fields of view. Because the plume brightening events are unpredictable (but happen at a global rate on the order of a few per hour), this is something of a "fishing expedition", wherein the entire coronal hole will be observed, and "interesting" events picked out post facto. Operational overview: Originally, this was conceived as an 8-hour add-on to the J2 tests (during a "normal" DSN long contact). However, with the J2 delayed till the end of March, it is likely that a longer observing time will be possible during one of the 16-hour intervals originally scheduled for the SoHO J2, probably on March 7. Observations will take place over a complete long DSN pass (specific times TBA March 1). The JOP activities will start just before the off-point, when LASCO will take an exposure of the outer corona through their C3 camera before closing the door for the off-point.[1] EIT will also take and downlink an exposure of the full disk in their Fe IX/X band before the off-point. The EIT image will be used to correct the other instruments' pointing, if necessary, for the rest of the observation. During the off-point, each instrument will view the appropriate part of the plume, as described below. In general, the lower instruments will use higher cadences, with the highest cadence for the instruments watching the footpoint. MDI will take magnetograms and other photospheric images on a one-minute cadence. UVCS, viewing the upper reaches of the plumes from 1.5 R0 to 4 R0, takes 3 hours to complete one radial scan (though time resolution may be enhanced through raster interleaving). Individual observation plans are discussed in more detail below, on a per-instrument basis. [1] (Depending on J2 scheduling, this might happen before or after the off-point, or both). Instruments ----------- MDI (Craig DeForest, cdeforest@solar.stanford.edu) MDI will observe magnetic activity at high temporal and spatial resolution, to constrain magnetic energy input at the bases of the plumes. High-cadence observations of the South pole region will occur over a 500 x 350 arcsec rectangle centered on the N/S line and including the Southern limb. Each minute, a magnetogram and one other data product will be downloaded. This cadence will be maintained for the entire observation period, subject to occasional one-minute interruptions. CDS (Richard Harrison) In support of JOP 39 it is proposed that CDS is used to home in on the base of the plume structures. To attempt to detect the plumes themselves with CDS would involve very long exposures and cadence times. Since SUMER and UVCS will see the plumes, this observation would not be as useful as a thorough scan over short periods of the roots of the plumes. Thus, it is proposed to use the EJECT study. The details of EJECT are given below: Spectrometer - Normal Incidence Raster Area - 4 x 4 arcminutes Slit - 4 x 240 arcsec Locations per raster - 60 Step size - 4 arcsec Exposure time per step - 3 sec Compression Scheme - Sum over wavelength Wavelength Selection: Fe VIX 334.17A Si IX 341.93A He I 584.33A Si IX 349.87A Mg IX 368.06A O V 629.73A (Good T range, well separated lines, some diagnostic capabilities). Total Duration of Each Raster Scan- 6 min 25 sec. Pointing - Sit just inside limb (centre perhaps 1 arcmin inside of the N pole; subject to modification based on EIT Quicklook) SUMER (Rep: Phillipe LeMaire) SUMER can image plumes in individual spectral lines by scanning their spectrometer slit. Several slow scans will be performed, on about a one hour cadence, over a rectangular region above the South Pole limb up to approximately 1.2 RO. Line profiles will be extracted in Ly B and the O VI doublet. EIT (Rep: Joe Gurman) EIT will provide quick-look data to guide site selection in the coronal hole, and high-cadence observations of the footpoints and lower coronal parts of several plumes. Relatively high time resolution (2-3 min) is possible throughout the lower corona, allowing tracking of density variation in the footpoints and lower reaches of individual plumes. By comparing images taken at different wavelengths, it should be possible to directly measure electron density and temperature in the visible structures. EIT will provide several full-field images of the offset Sun prior to the off-point. At the start and end, they will take deep exposures in the Fe IX/X band, to try resolving structures as far out as possible. For most of the observing period, EIT will be generating 800x1200 arcsec subfield images centered over the South coronal hole, on a ~180 sec cadence, in Fe IX/X. Some time will be devoted to higher-cadence images at 304A. UVCS (Rep: Silvano Fineschi) UVCS has the capability to measure electron densities and velocities along plumes in the mid corona where transonic acceleration occurs. This should allow a rough determination of where the bulk of the plume acceleration energy comes from: the footpoint activity; or some acceleration or heat deposition mechanism higher up. In addition, it allows tracking of individual plume structures out to the LASCO C3 field of view for observation beyond the critical point. UVCS will make a minimum of two raster scans, each in both O VI and Ly A, of the entire region over the pole, from R=1.5 to R=4. Each full resolution scan takes ~3 hours to complete; to improve time resolution, some raster interleaving may be done. LASCO LASCO can track plume flow out into the solar wind domain. As the LASCO C1, C2, and C3 doors must remain closed during the off-point, C1, C2, and C3 images will be available only from just before and just after the offset point. This will allow feature tracking and density variation analysis from R=1.1 to R=30. OUTSIDE COLLABORATIONS ---------------------- YOHKOH Yohkoh's SXT will be providing higher-than-normal cadence full-disk images in soft X-rays (at least two during the JOP period), to help constrain temperatures and/or set upper limits on SXR flux from plume footpoints and flux tubes. They may be able to provide higher cadence subfields, as well. Details will be worked out as the week progresses. GROUND-BASED SUPPORT We are contacting the Usual Suspects, including HAO (for images from the Mk II K-Coronagraph) and NSO (for H-Alpha images). Any interested parties, please contact Craig DeForest (cdeforest@solar.stanford.edu) for more detailed coordination.