2  99 sigmoid

During the third Whole Sun Month Campaign (August 18 - September 14, 1999), the evolution of the Active Region NOAA 8668 was followed during its meridian passage and at the limb, with simultaneous observations with SOHO and other instruments, both satellite and ground-based. This active region presented a sigmoidal (S-shaped) structure as seen in the X-rays, had a filament associated with it, and was very active.

On August 21st, a small flare occurred (at @ 17:40 UT). This was associated with a brightening of the sigmoidal structure and a later disappearance of the filament.

Details can be found in Del Zanna et al. (2002) and Gibson et al. (2002).

For the first time, spatially-resolved maps of blue-shifts in coronal lines during the decaying phase of a small flare are presented. These blue-shifts were located at the two ends of a small loop system and can be interpreted as indirect evidence of chromospheric evaporation. Fe XIX emission showed some interesting properties, including a pre-flare enhancement along the loop structure.

Figure 1: A sequence of CDS rasters of the Sigmoid, showing the small flare (17:44 UT). From top to bottom: monochromatic images of O V (transition region), Mg X (lower corona), Si XII (upper corona); velocity map as derived from the Si XII line profiles; monochromatic images of the Fe XIX flare line. All images in a row are plotted with the same intensity scale (shown in the third panel: phot cm^-2 s^-1 arcs^-2) for the line intensities and Km/s for the velocity map). The central time of each raster is indicated.