Multi-Wavelength Observation of the 3n/x3.3 Flare of 28 November 1998

Abstract

The 3N/X3.3 flare of 28 November 1998 was observed in multiple wavelength simultaneously. The available data include Hα images, spectra in He i 1083 nm and Ca ii 854.2 nm from Purple Mountain Observatory (PMO), soft X-ray (SXR) and hard X-ray (HXR) images and flux from Yohkoh. Morphological relationship investigation and spectral analysis of these data show: (1) The sudden brightening at loop top above the active region and the steep increase of SXR flux before flare onset suggest that the corona there had already been heated to some extent in the preflare phase. (2) The scales of the Ca ii 854.2 nm emission areas are very similar to those of the Hα line, but the emission profiles look like those of the Ca ii K line. Most of the He i 1083 nm emissions exist in the bright Hα kernels and can last to the decay phase. (3) Flare spectra show that line shift and asymmetry are very common in this flare not only in the impulsive phase but also in the decay phase. The difference in the line shifts or asymmetry between Ca ii 854.2 nm and He i 1083 nm, as well as the difference between the line center and wings of Ca ii 854.2 nm imply the existence of a velocity gradient in the line-of-sight direction. (4) Post-flare loops with very deep absorption (≈ 70%) and very-high-velocity red shifts (30–90 km s−1) were observed in He i 1083 nm during the decay phase. However, only a slight dip can be found in the Ca ii 854.2 nm profile.