Received: February 2, 2000; latest revision March 17, 2000

Participating Instruments and Observatories:

SoHO-CDS/EIT/LASCO/MDI/UVCS
TRACE
YOHKOH/SXT
Mees Solar Observatory

Objectives
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• To obtain multi-wavelength observations of evolving magnetic structures as a sigmoidal active region evolves prior to and following an eruption.
• To establish the extent by which sigmoids and H-alpha filaments are connected.
• To determine temperature and density structure throughout the sigmoid region, from corona to photosphere, both before and after the sigmoid erupts. Does a comparison show material being lost?
• To compare remote, coronal observations of temperature with those observed in situ at 1AU via detection of highly ionised particles of solar origin at 1AU.

Target
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This campaign will be run as an interrupt study; yohkoh/SXT and SoHO-EIT full disk images will be studied until a candidate active region; judged to be sigmoidal, is visible on the disk. At this time, all other instruments will be asked to alter their pointing accordingly. Observations will coincide with the Mees Solar Observatory Observer's hours; normally between 17 - 23 UT Monday to Friday.

Summary of Planned Observations

Space-Based Observations

SoHO-CDS
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Continuous tracking of target active region. Look for sigmoidal structures at lower temperatures. Temperature and density diagnostics will be used to map cooler regions beneath X-ray sigmoid. Data prior to an eruption could be compared to that observed following an event, in order to establish what material, if any, has been removed. This study will incorporate FeXIV(334 & 353) data in order to provide density diagnostics, FeXVI(360), in combination with FeXIV, to produce temperature maps and finally, OV(629) and HeI(584).

CDS study SIG_EVOL: Sigmoidal Active Region Evolution has been created specifically for SoHO JOP 120 and consists of a single raster. On location of a sigmoidal target region, this will be executed as many consecutive times as possible. Each raster will consist of a 240x240 arc sec field of view at 4x4 arc sec resolution, a single execution of which will take approximately 23 minutes.

SoHO-EIT
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Normal synoptic observations.

SoHO-LASCO
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Normal synoptic observations.

SoHO-MDI
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Full disk line of sight magnetograms taken at highest available cadence are desired. High resolution data at highest available cadence are preferred, should candidate active region fall within MDI's high resolution field. Should other instrument commitments result in high resolution data being unavailable, or the telemetry required for high cadence data be unavailable, 96 minute cadence full disk magnetograms will be sufficient.

SoHO-UVCS
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UVCS will point off limb, making alternate observations at 1.7, 2.3 and 2.6 Ro. Major lines will be OV](1218), OVI (1032,1037), Ly-Alpha (1216), Ly-Beta (1025), N III (989,991), CIII (977), Si XII (499) and Mg X (609). In the event of a CME, this range of emission lines will give structure and line of sight information for the expanding magnetic cloud.

Trace
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Used to provide highest possible spatial and temporal resolution during the sigmoid's evolution. High resolution images will be taken in the Fe IX(171), FeXII(195) and FeXV(284) lines. High resolution HI L-alpha(1216) and CIV(1550,1600) data will also be taken.

Yohkoh/SXT
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Used to define the appearance of a 'sigmoid'. On location of a suitable target region, fixed pointing mode will be used, such that the field of view remain centered on the sigmoid.

During quiet mode observations, wherever possible, SXT will switch from the more normal FFI-dominant mode to PFI-dominant mode; thus further increasing the number of partial frame images over full frame images. During PFI-dominant mode, two sets of 2x2 full resolution, fixed exposure partial frame images will be taken using the thin aluminium (Al.1) and Dagwood (AlMg) filters. However, during FFI dominant mode, this will be replaced by two sets of 1x1 full resolution, fixed exposure PFIs and one half-resolution 1x1 PFI, again using thin aluminium and Dagwood filters.

Flare tables will be used as standard.

Ground Based Observations

Mees Solar Observatory
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Continuous coverage of AR using Imaging Vector Magnetograph (IVM) and Haleakala Stokes Polarimeter (HSP) providing highest possible spatial and temporal resolution vector magnetograms. Data will allow observations of the changing structure of the magnetic field as the sigmoid develops. Calculation of active region current maps will give further insight into processes causing sigmoid formation.

H-alpha data using Mees CCD Imaging spectrograph allowing observation of filament morphology before and after an event. Data should be taken at highest possible cadence, with observations in the blue and red wings of the H-alpha centreline.