Using the Coronal Diagnostic Spectrometer (CDS) on SOHO spacecraft, we observed the temporal evolution of an active region NOAA #9254 from December 6 to 9, 2000. Within an field-of-view of 122" x 121" (89000 km), the CDS observed the AR9254 with a time resolution of 30 minutes in 10 spectral lines; Fe XVI 360.76A (2.5MK), Si XII 520.66A (1.8MK), Mg X 624.94A (1.1MK), Mg IX 367.93A (1.0MK), Ca X 557.98A (0.7MK), Ne VI 562.83A (0.4MK), O V 629.39A (0.2MK), O III 599.59A (0.1MK), He II 607.71A, and He I 584.33A, which can see dynamics in different layers of the solar atmosphere from the chromosphere through to the corona. Although the AR9254 did not produce a flare during the CDS observation period, the CDS raster images show formation and decay of a sigmoidal (S-shaped) structure in a high temperature line (Fe XVI) while it appeared as a double ribbon (Si XII, Mg X, He) or triple patches (Ne VI, O) in lower temperature lines. We obtained velocity maps in the Fe line that show upward and downward motion concentrated along the eastern and western edge of the sigmoid, respectively.

Solar sigmoidal structure is generally remarkable in soft X-ray images (>2MK) and is known as a manifestation of highly sheared structures (Rust & Kumar 1996). It often marks the source region of a coronal mass ejection (CME). Previous studies on sigmoids have focused on the magnetic topology (e.g., helicity and shear buildup) and connection with the CME, and thus the physical process involved in sigmoid formation is still not well addressed (e.g., Pevtsov et al. 1996). By combining the CDS images with Yohkoh/SXT(soft X-ray), TRACE and SOHO/EIT(EUV), Hiraiso H alpha images, and SOHO/MDI and MSFC magnetograms, we discuss the formation scenario of sigmoids.

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