August 11, 1999 Eclipse

SOHO & TRACE
Ground-Based Expedition
Support Requests


Ground-Based Expeditions Requesting SOHO & TRACE Support


ESA SPACE SCIENCE DEPARTMENT
MULTI-SITE EUROPEAN CAMPAIGN

CONTACT PERSONS:

Salvatore Orlando (orlando@so.estec.esa.nl )
Bernard H. Foing (bfoing@estec.esa.nl)

INSTITUTIONS:

Solar System Division, ESA Space Science Dept., ESTEC

LOCATION:

Szombathely (Hungary)

ECLIPSE TIMES:

Totality at Szombathely (Hungary), 10:46:23 - 10:48:45 UT;
Multi-site observing campaign from UK (10:10 UT) to Romania (11:10 UT)

GOAL OF OBSERVATIONS:

  1. Determination of equivalent coronal densities and temperature in coronal plumes and streamers
  2. High resolution coronal observations in stereo with SOHO
  3. Measure of extended cool material distribution in the corona in H alpha

TYPES OF OBSERVATIONS:

SOHO OBSERVATIONS REQUIRED BEFORE ECLIPSE:

FULL DESCRIPTION:

The Space Science Department (SSD) of ESA is organizing a multi-site observing campaign (UK, France, Germany, Austria, Hungary, Romania) to be coordinated with SOHO. A multi-site eclipse campaign will provide a longer sequence of coronal observations (from 10:10 UT to 11:10 UT). Some of the eclipse images will be transmitted for live internet distribution.

The core SSD science experiments will be set in Szombathely (Hungary), where the totality is expected from 10:46:23 to 10:48:45 UT on August 11, 1999. The main objectives of the expedition are to study temperature and density structure and dynamics in the corona, and to search for cool material in the very hot corona. These eclipse results will be analyzed with SOHO data. More specifically, the scientific objectives of the SOHO-coordinated Eclipse campaign are:

  1. Determination of equivalent coronal densities and temperature in coronal plumes and streamers in coordination with LASCO and MDI on SOHO;
  2. High resolution coronal observations in stereo with SOHO;
  3. Measure of extended cool material distribution in the corona in H alpha in coordination with EIT and CDS on board SOHO.

For the experiment A, LASCO C2 and C3 will support the expedition with synoptic observations in white-light over the range 2-30 solar radii, completing the ground-based eclipse observations in white-light over the range 1-2 solar radii. During the totality in Szombathely (10:47 UT +/- 15 mn), LASCO C1 will provide observations in the green corona line of Fe XIV (at 5303 A) over a 1.1-3 solar radii field of view, giving information on the inner corona plasma at 2e6 K. The synoptic observations from MDI will provide a map of the surface magnetic field to be compared with 3-D coronal structures.

For the experiment C, the main purpose is to analyze the presence of cool material distribution in the corona. An important aspect of this program is the search for cool material in the very hot corona of active regions. The program we propose aims to identify an active region and/or loops evident against the dark background at the solar limb during the totality in Szombathely (10:47 UT +/- 15 mn). Then we propose to coordinate the ground-based eclipse observations of the active region (loop) selected with the observations from SOHO in the light of many emission lines simultaneously so as to study the coronal plasma conditions over a wide range of temperatures, from chromospheric to coronal ones. For this program, the request for SOHO observations is the following:

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WILLIAMS COLLEGE EXPEDITION

CONTACT PERSONS:

Jay Pasachoff (jmp@williams.edu )

INSTITUTIONS:

Williams College

GOAL OF OBSERVATIONS:

To provide CCD green-line observations of the middle corona to extend the EIT observations to higher coronal levels and to bridge the gap between the EIT and the LASCO C2 images. The images will be reduced in radial-filter mode to show the magnetic-field structure over 3 solar radii, and how it links with the disk structures observed with EIT. The similar 1998 eclipse observations could also be used to assess the scattered light in LASCO C1, a comparison we are scheduled to make in the fall. Williams College Expedition is planning to observe at or near the 5303 line with a field of view matching the C1 LASCO coronagraph, in formal liaison with EIT. We hope for an EIT sequence as close as possible to eclipse time at the peak of the eclipse in Ramnicu Valcea, Romania, UT 11:02-11:04.

Our image taken at the 1998 eclipse matching the C1 observations and merged with an EIT image, and a color image (with a simulated radial filter) merged with an EIT temperature ratio map are posted at http://www.williams.edu/Astronomy/eclipse98.

TYPES OF EQUIPMENT:

  1. A specially made camera with a 2" 300-mm focal-length coated lens feeding a DayStar 3-A-passband 5303-A green-line [Fe XIV] filter and a Photometrics 512x512 CCD. The field of view is about 3 degrees. This CCD image from the 1998 eclipse appears low down on the URL www.williams.edu/Astronomy/eclipse99, both with an EIT center and, later, as color isophotes.
  2. A high-resolution green-line [Fe XIV] 5303 A image taken at 10 Hz cadence of a quarter of the corona using a 3-A-passband DayStar filter and a Princeton Instruments CCD with a 300x150 pixel image read out with 2 arcsec pixels.
  3. Film cameras showing the whole corona from which radial-filter-equivalent images will be displayed such as that heading www.williams.edu/Astronomy/eclipse99 and www.williams.edu/Astornomy/eclipse99/composite, the latter of which shows our radial-filter-equivalent both with and without the EIT image.

LOCATION:

Ramnicu-Valcea, Romania 24 deg 22'E 45 deg 06'N

SOHO OBSERVATIONS REQUESTED:

A set of EIT observations at each wavelength as close to UT 11:02-11:04 as possible, as well as LASCO C2 and C3 observations also as close as possible. These times are the peak of the eclipse.

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SOLAR ECLIPSE CORONAL IMAGING SYSTEM
(SECIS) EXPEDITION

CONTACT PERSONS:

Ken Phillips, Principal Investigator ( K.J.H.Phillips@rlac.uk )
Peter Gallagher ( P.Gallagher@qub.ac.uk )

INSTITUTIONS:

Rutherford Appleton Laboratory (RAL)

GOAL OF OBSERVATIONS:

To search for fast changes and possible periodicities in the green-line coronal emission. This may be used to identify the source of the heating of the solar corona in the form of either travelling waves or short-lived phenomena that might be related to nano-flares. Refer to SECIS WWW site for more details.

TYPES OF EQUIPMENT:

A tracking mirror or heliostat directs sunlight into the horizontally mounted telescope. A beam splitter along the optical path directs light into two CCD cameras, one with a 530.3 nm (green line) filter, the other with a broad-band (10 nm) filter at about 550 nm. The instrument will image the solar corona during eclipse totality with a spatial resolution of about 1.75 arcsecs over a sky area of approximately 0.5x0.5 solar radii. A specific region will be chosen from inspection of Yohkoh and SOHO images immediately before the eclipse. Refer to SECIS WWW site for more details.

SOHO OBSERVATIONS REQUIRED BEFORE ECLIPSE:

- CDS: Full Sun Scans

SOHO OBSERVATIONS DURING THE ECLIPSE:

- CDS: Scans on selected 4x4 arcmin region across the eclipse timeframe

SOHO OBSERVATIONS AFTER ECLIPSE:

- CDS: Full Sun Scans

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Royal Observatory of Belgium and JOSO TECONet Expedition

CONTACT PERSONS:

Frederic Clette (fred@oma.be )

INSTITUTIONS:

Royal Observatory of Belgium (ROB)
Joint Organisation for Solar Observations (JOSO)

LOCATION:

TECONet (Trans-European Coronal Observing Network): France to India
Reference stations :
- Niederbronn-les-Bains, France > Long: -07d39m, Lat: +48d58m, Alt: 250m
- Rimnicu-Vilcea, Romania > Long: -24d22m, Lat: +45d06m, Alt: 100m

ECLIPSE TIMES:

START : 10h20m UT
END : 11h40m UT for European segment, 12h35m UT for India
Reference stations :
- Niederbronn-les-Bains, France > Mid-totality : 10h31m UT
- Rimnicu-Vilcea, Romania > Mid-totality : 11h03m UT

GOAL OF OBSERVATIONS:

SOHO JOINT OBSERVATIONS:

TYPES OF OBSERVATIONS:

SOHO OBSERVATIONS REQUIRED:

For more details, see the JOSO TECONet page

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Expedition of French Institutes to Iran

CONTACT PERSONS / INSTITUTIONS:

Institut d'Astrophysique de Paris- CNRS/ leading Organization:
Dr. S. Koutchmy; J. Mouette; P-A. Grorod

Institut d'Astrophysique Spatiale- CNRS, Univ. Paris XI & Obs. de Paris:
Dr. F. Baudin; Dr. K. Bocchialini

Laboratoire d'Astronomie Spatiale- Marseille (CNRS): Dr. Ph. Lamy

Societe Astronomique de France (SAF):
Mr R. Leguet; Mr. C. LeRoux; Mr. G. Mahoux; Dr. R. Robley in collaboration with a team from the Tabriz University (Iran): Dr. A. Adjabshirizadeh et al.

GOAL OF OBSERVATIONS:

Observations to be performed from a mountain site in Iran, near Ispahan- 100 km toward NWW. Probability of having a clear sky is 95%; altitude 2200 m; totality will occur at U.T. 12:03. The corona is expected to have the shape of a pre-maximum corona close to the polatity reversal at the N-pole but not at all in the S-pole region. Prominences and active regions at the limb should be observed, as well as streamers in projection over the N-pole.

SOHO OBSERVATIONS REQUIRED BEFORE ECLIPSE:

  1. The priority is to make 1 full frame of EIT image with the 304 filter exactly (+/_ 1 mn) at the time of the totality of the selected site in Iran: 12:03 UT !!! Repeating the shot just before and after (+/- 3 mn) could be a good idea but it is not a priority.
  2. Take full frames of CORONAL EIT images (195/171/284) before and after (+/- 30 mn or less) 12:00 UT
  3. Take Lasco-C2 and C3 frames before and after (+/- 6 hours at a 30 mn minimum cadence) 12:00 UT.

MAIN EXPERIMENTS:

  • Coronal imaging ---

    We concentrate on the INTERMEDIATE W-L corona (between the very inner corona, where loops and jets dominate, and the outer corona, where the outward flow dominates) which cannot be measured from space due to the vignetting by occulting systems.

    We do an absolute photometry using simultaneously imaged stars in the same field of view. A precise polarimetry is planned as well as the use of a radial gradient filter of 150 mm diameter. These data are required to complement spaceborne observations regarding the precise measurements of plasma densities in the main part of the corona. They will be compared to the values recently obtained during the solar minimum. High spatial resolution imaging is an other advantage of the method.

    We also plan to do some deep imaging to look at the so-called cool corona around the occulting Moon, in Halpha, KCaII lines and narrow-band continuum. For that, we use both radial filters of 50 mm diameter and narrow band interference filters with small telescopes. Both photographic film and CCD camera are used.

    The hot topic considered with this last set up is the analysis of the recently discovered solar PROLATENESS (ovalization) at the high chromospheric level (e.g. AA:1998, 336, L57); we want to go further out in the low corona. Until now, the prolateness was measured only up to 6 to 7000 km heights, using EIT(SoHO)-HeII emissions and, of course, at lower levels in Halpha, KCaII, etc. In Halpha the prolateness is well seen up to the 'top' of spicules and could be a fundamental indicator of the mechanism converting the magnetic turbulence energy into convecting plasma flow near separatrix layers.

  • Spectroscopic experiments ---

    We prepared spectrogaphs for both i) HIGH dispersion to look at the profile of the FeXIV coronal emission line for different radial distances and different position angles, and ii) LOW dispersion analysis to simultaneously look at several lines and deduce the temperature inhomogeneities of the whole corona.

    High sensitive film and CCD DV-cameras are selected as detectors.

    High dispersion is used to look at the properties of propagating waves in the intermediate corona, thanks to the measurement of the Doppler effects, including the Doppler widths, and the determination of the so-called non-thermal velocities as a function of radial distances and latitudes. We plan to get data up to 2 solar radii from the sun's center, based on previous experiences (Chili 94 and Guadeloupe 98).

    Low dispersion is used to simultaneously measure several forbidden lines and look at the temperature inhomogeneities at large scale (+/- 3 solar radii) from the analysis of the distribution of the emission measures. Electron temperatures will also tentatively be studied, using the Grotrian's method over the bMgI and DNaI lines.
    The use of new-technology fast CCD cameras should be relatively efficient at eclipses. We hope to significantly improve what has been done in the past with plates and films, although new fine-grain films are also available. Further, the coordinated effort (with ESA, NASA and ISAS) to perform well defined and selected observations using the spaceborne facilities, especially the CDS, SUMER, EIT and the LASCO exp-ts of the SoHO mission, the SXT of YOHKOH and possibly, the TRACE mission, makes our observations more effective than it was in the past. We have now an excellent coverage of coronal phenomena occuring before and after the eclipse which makes eclipse results more reliable and more effective to process and to interpret.
    During the total eclipse, a large amount of photons is available (the corona is as bright as a full Moon) such that it is more easy and evidently cheaper to conduct sophisticated investigations, especially at high resolution and dispersion. Of course, this is possible during just the short time (a few min) of the totality! Only spaceborne observations and long duration missions permit a survey of coronal and solar phenomena.

  • SELECTED RESULTS OF PRECEDING ECLIPSE OBSERVATIONS

    The results of our 1991 observations are published in a series of papers in Astron.Astrophys., Astr.Rep. and ApJ. We discovered very fine W-L structures at the base of the intermediate corona (down to the 300 km scales); some of them have short lifetime (like 40 sec). During more than 200 sec at high cadence we got what we believe is a coronal plasmoid (small cloud of 2000 km diameter with changing shape, moving at 100 km/s speed) which travelled across more radial coronal structures (a spectacular movie was assembled), showing interactions leading to a splitting of its core, etc.

    The dynamics of the corona at small scales was found surprisingly large; the so-called turbulence seen on coronal line profiles (20 to 30 km/s) is resolved in the inner corona at scales under 1". To give a good idea of what was seen in 1991, let us mention that the dynamics is already evidenced watching the original W-L video movie of a narrow fov (80" size), without introducing any acceleration. These CFHT data confirm our earlier observations of plasmoids and jets (spike) obtained since 1973.

    From our large scale images taken in 1991 (active corona) with a radial filter from 2 different locations (Hawaii and Brazil) with a 1H 40 mn separation in time, we compared the position of SHARP EDGES of streamers and we succeeded in using the effect of the so-called rigid rotation of the corona to look at the 3-D structure (stereo-effect) /results published in Nature 1992, 360, 717 in collaboration with russian scientists/.

    Results tell us that the coronal plasma at large scale is well confined in sheets and the topology of those sheets is a new very interesting topic we are trying to consider using numerical simulations (paper in press in collaboration with IZMIRAN).

    We intend to repeat this exp-t in collaboration with the team from Kiev; however, the Lasco/SoHO coronagraphs accumulated a large number of W-L images of the more external corona and we can now look at these images and improve our eclipse results.

    From our 1994 spectroscopic exp-t, using a long slit, we got the line profiles of the green line of FeXIV in several locations, with the following main conclusions:

    Over one polar region, the profiles are broader but intensities are really low, although well measurable up to 0.2 solar radii (coronal hole boundaries; plumes, etc.) from the limb. They tell us that small regions with 2 millions kelvin ionic temperature definitely exist over the poles. These regions could be related to the locations where X-ray polar jetlets (Yohkoh observations, see AA, 1997, 320, L33) are observed and where magnetic reconnections are occuring.

    Over the equatorial regions, we measured line profiles of large intensity, in streamers, and even some small but significant (#10 km/s) line shifts at radial distances of 0.5 and more from the limb. We think that a large part of the broadening could be due to ubiquitous propagating waves which could explain the acceleration of the slow wind. Those propagating magneto-acoustic waves were quite recently seen using chromospheric lines formed in the network (AA:1995, 299, 893; AA:1996, 314, L9). However, it is not yet clear what is the best diagnostic to reveal reconnections (temperature effects; plasmoids..) and/or propagating waves (Doppler effects) and their dissipation, taking into account the brievity e.g. limitations of eclipse observations. More works is needed at the forthcoming eclipses of the next Millennium !!!

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    HAO EXPERIMENT

    CONTACT PERSONS:

    Bruce Lites , David Elmore, Philip Judge

    INSTITUTIONS: HAO, NCAR

    LOCATION: Austria

    OUTLINE:

    We request observations from SOHO-EIT and TRACE in support of an experiment based in Austria. Following the successful experiment ran from Curacao on Feb 26 1998 (Lites et al., Solar Physics to be submitted), we will field an experiment designed to 0.5 second cadence, 1 arc-second pixel size, broadband red light images of the corona just above the solar limb with a field of about 10 by 8 arc minutes.

    One of the goals of the 1999 eclipse expedition is to verify the presence of very small amplitude perturbations of the broad-band visible light corona in the region of polar plumes, as revealed by the 1998 Curacao observations. Rapid cadence, high precision and rather high angular resolution observations are required by the ground based instrument. The fortuitous occurrence of an EUV jet during totality of the 1998 eclipse emphasized the value of EUV simultaneous EUV observations. Therefore we request a similar time series of EUV observations from both TRACE and SOHO/EIT for the time around totality in Austria (details will be provided if the EUV observations are approved). The EUV observations, together with the visible light observations that are sensitive to coronal electron density only, one may tightly constrain the density and temperature fluctuations of the observed dynamical events.

    Based upon the present state of the corona, the target most likely is the north polar region.

    REQUESTED SUPPORT:

    The requested support ideally consists of two parts:

    1. For a 20 minute period centered on the time of totality in Austria, high cadence observations are requested with both EIT and TRACE, in the 171 and 195 bandpasses. TRACE is required to make the best possible cadence match to the ground based data. With the TRACE team we would seek to develop a suitable sequence, for instance 10 second cadence 171 images, or a longer cadence mix of 171 and 195 images over a suitable field of view. The ~20 minute period is needed to look for periodic (3 minute period?) resolvable changes in intensity arising from Alfvenic propagation of photospheric disturbances into the corona.
    2. prior to and after the timeseries, we would like a few context images of the coronal hole with EIT and TRACE, in all wavelength bands.

    OVERVIEW OF RESULTS FROM 1998 ECLIPSE- WHITE LIGHT+EIT

    Lites et al (1999) recorded changes in the white-light coronal emission during the 3.3 minutes of totality of the 1998 total solar eclipse at Curacao, Netherlands Antillies.

    The most prominent of these changes is associated with an EUV jet (region "a" in the figures) that is embedded in a polar plume near the south solar pole. This disturbance appears to propagate radially away from the Sun at speeds of about 200 km/s as observed in both white light and Fe XII 195. The appearance of this jet in the EUV image sequence shows it to be a very narrow structure (its width is only about 5 arcsec near the solar limb) that simultaneously moves both outward and from right to left (west-east). Furthermore, the EUV image sequence reveals that the emission source of the jet and plume at the base of the corona undergoes a slight but definite corresponding motion from west-east. The observational facts constrain the possible nature of the jet phenomenon, related to the magnetic enviroment at the base of the corona. Lites et al. discuss models involving bi-polar magentic structure in the coronal hole region.

    Other perturbations seen in the PEPPI image sequences in the loop and streamer structure (e.g. features `f', `g', `h', and `i' sustain hope that some day one might identify propagating Alfven waves in the corona. The duration of totality appears to be be too short to measure propagation speeds for these disturbances, and the level of the disturbance is too low to allow us to say much about their other observed properties, even the direction of propagation along the loops. It is not clear that eclipse measurements similar to those of PEPPI will add substantial new information: the duration of totality is simply too short. However, coupled with longer timeseries data from EIT and TRACE spanning the 1999 Aug 11 eclipse, such data may hold the key to better understanding of these disturbances and their consequences for heating the corona.

    Figure 1 (postscript) Fig 1: The upper left panel shows a radially enhanced PEPPI image at the start of totality. The darkened region at the tops of each image is a mask applied for all positions < 20 arcsec above the lunar limb at second contact. Sobel edge enhancement of the PEPPI image in the upper right panel reveals fine structure in the image that largely persists throughout the eclipse. The lower left panel is a difference of summed images near the end of totality from that near the start of totality. Features indicated by letters in the images are discussed in the text. Lines of constant normalized solar radial coordinate from 1.05 to 1.30 shown in the lower left panel trace the locations of the inferred fluctuations in fractional intensity variation shown in the lower right panel, where the tick spacing on the ordinate is 0.01.

    Figure 2 (postscript) Fig 2: The ratio of emission in the bands 195/171 is shown on a logarithmic intensity scale to accommodate the substantial range of this ratio within the image. The images were obtained at 16:00/15:46 UT on the day of the eclipse. The low relative emission in Fe XII (171) in this south polar region, including polar plumes, indicates temperatures below 1 MK.

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    SAO EXPEDITION

    CONTACT PERSONS: Silvano Fineschi

    INSTITUTIONS: SAO

    GOAL:

    SAO expedition in Syria (broad-band pB of the K corona at heliocentric heights: 1.1 - 2.5 solar radii)

    SOHO OBSERVATIONS DURING THE ECLIPSE:

    Support from UVCS and LASCO requested.

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    BUCHAREST EXPEDITION

    CONTACT PERSONS: Silvano Fineschi

    INSTITUTIONS: SAO

    GOAL:

    French-Czechoslovakian observation from Bucharest ground-based observatory in Romania (visible light narrow-band spectroscopy of the Rayleigh emission from coronal neutral hydrogen)

    SOHO OBSERVATIONS DURING THE ECLIPSE:

    Support from UVCS and LASCO requested.

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