SOHO JOP048 COMPREHENSIVE POLAR PLUME OBSERVATIONS Proposal and preliminary observing plan --------------------------------------- Craig DeForest (MDI) 16-July-96 Introduction and Overview: -------------------------- While the results from JOP 039, the south pole observation campaign that was run in March of 1996, have not yet been completely analysed, they have already generated very interesting results: Plumes appear to have very strong unipolar magnetic footpoints, with fields as strong as several hundred gauss (compared to the average field of 1 gauss throughout the hole); many transient heating events were observed, some of which appear to have no strong transient magnetic signature; plume geometry is being tracked from the photosphere out to 30 R0 (with LASCO); and plume outflow speeds have been directly measured (by UVCS via doppler dimming) to be ~200 km/sec at 1.8 R0. Questions raised by these preliminary analyses, and experience gained from JOP-39, motivate another comprehensive plume observation campaign. The proposed campaign will involve a full day of intensively coordinated observations on the part of most SoHO instruments; and several days' semi-independent activity on the part of some instruments. Scheduling Constraints: ----------------------- The most favorable B-angle for N pole observation occurs in late summer / early fall. Ground-based coordination is better in early to mid August. I suggest running this JOP either in mid August (when weather is likely to be better at the ground based observatories) or in early September (when the B angle is slightly more favorable). Science goals: -------------- Several specific science goals have arisen from preliminary analysis of the JOP-039 data. Many of these goals could be satisfied by another one-day-long coordinated observation.: * EIT has observed several interesting impulsive events that may be related to plume birth. It would be great to catch several more in a relatively high time resolution study (a few minutes to tens of minutes) with EIT, and compare with magnetic and chromospheric signatures on the surface. It may be possible to track the ejecta from these events with the LASCO cameras. [Contact: Joe Gurman, EIT] * Several plumes have been tracked out through the various imaging instruments' fields of view in JOP-039. Alignment and correspondence are good between features observed by MDI, EIT, the HAO Mk III Coronagraph, and LASCO C2, suggesting that XUV plumes are white-light rays, and that a necessary (but not sufficient) condition for their existence is a strong, unipolar magnetic footpoint. With the experience from JOP-39, we can generate an even clearer, cleaner data set that will allow tighter constraints on plume models. * Plume outflow velocities have been directly measured by UVCS at a small number of altitudes. UVCS also measured the time variability of plumes during JOP-39, and determined that, at altitudes >1.5 R0, they do not vary significantly (more than 10%) in brightness over periods of a few dozen minutes; this allows us to use longer exposures and accumulate better photon statistics with UVCS and SUMER. [Contact: Silvano Fineschi, UVCS] * We have yet to observe (reproducibly) the birth or death of a plume -- though there are several candidate events in the EIT movies. The nature of plume birth and death play an important role in choosing a model for these hard-to-heat features. A class of "air/fuel/spark"-type models (in which several ingredients, plus an "ignition" event, are required to make a plume) will be either strongly suggested or weakly ruled out by the nature of plume birth. * It's not clear, from the EIT and MDI observations alone, whether plume footpoints occur within network cells or on their boundaries. This, and other relevant questions having to do with footpoint activity, conductive heat loss, and time variability, could be answered by a more complete, concurrent of imaged footpoint spectra from CDS. In light of these, and other, developments, I'd like to see another coordinated plume observation with: * More time-resolved spectra of the chromosphere from CDS, to get a closer look both at plume footpoints and at strongly magnetic non-plume regions; * less time resolution, more spatial coverage, and better photon statistics from SUMER and UVCS; * EIT exposure sequences with more than one wavelength at a time; * More time resolution in the LASCO C2 and C3 cameras than was possible during JOP 39 (due to the doors being closed then); and * More magnetic sensitivity and image stability in MDI than was possible during JOP 39 (due to the JOP-39 offpoint). Operational overview -------------------- Fully joint, high cadence observations will take place over one complete 8-hour DSN pass, with some instruments (eg UVCS) collecting relevant data over a longer interval. It is hoped that relevant but lower cadence observations from, eg, MDI, EIT and LASCO will be collected over a longer period, to provide more insight into the life cycle of individual plumes. Unlike JOP-39, there will be no S/C off-point; this means that MDI's magnetograms of the pole will be "full-disk" rather than "high resolution": pixel resolution will be 1.8 arcsec. It also means that the magnetograms will be more sensitive to low flux regions, because MDI's stabilization system only works without a S/C off-point. During the coordinated observations, MDI, CDS, and EIT will view the lower reaches of the plume structures with the highest cadence, to track impulsive events that may mark the birth of plumes. SUMER will scan over approx. 5-10 arcmin E-W just over the limb of the Sun; LASCO will generate polarization brightness images of the outer corona with C2 and C3, and Grotrian image pairs with C1; UVCS will observe line profiles and doppler dimming at several radii between 1.5 & 2.2 R0, over the 24 hour period surrounding the JOP. SOHO Instrument Plans --------------------- MDI (Craig DeForest, cdeforest@solar.stanford.edu) MDI will observe magnetic activity and photospheric motion at high temporal resolution, to constrain magnetic energy and mass flux input at the bases of the plumes. To identify network structure and motion, MDI will also collect intensity data (probably continuum; perhaps Ni line depth). High-cadence observations will occur over the full disk. Each minute, a magnetogram and an intensitygram or dopplergram will be downlinked. This cadence will be maintained for the entire 8-hour observation period, subject to occasional one-minute interruptions. CDS (Andrzej Fludra) [ NB: this is copied from Jop 39; More complete details will follow] 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 (Reps: Phillipe LeMaire, Don Hassler) 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. The cadence will be slow enough to ensure good photon statistics. EIT (Reps: Joe Gurman, Barbara Thompson) 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. The nature of EIT participartion depends greatly on the pending LASCO software upload, and on careful coordination with LASCO; more details will follow once EIT's capabilities are better known. LASCO (Reps: Simon Plunkett, Chris St. Cyr) LASCO can track plume flow out into the solar wind domain. Because there is not as much of a time constraint as during JOP-039, deep C3 exposures can be taken, as well as Grotrian image pairs in C1. Polarization brightness or white-light images, on a cadence of 1-3 hours, should be sufficient to track steady plume profiles. LASCO's capabilities depend strongly on the pending software upload, and should be carefully coordinated with EIT. More details will follow. UVCS (Reps: Silvano Fineschi, Gianinna Poletto) 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 C2 field of view for observation beyond the critical point. Gianinna Poletto has designed a long observation sequence to mesh with this JOP, with a compromise between spectral and temporal resolution. More details will follow. Non-SOHO Collaborations: ------------------------ YOHKOH We will contact Yohkoh scientists, prob. Nariaki Nitta and/or Loren Acton, regarding Yohkoh collaboration BBSO Hal Zirin has expressed an interest in a campaign similar to this one; detailed coordination will follow. [Others: high resolution magnetograms, poss. from KPNO; vector magnetograms]