Initial features of an x-class flare observed with SUMER and TRACE

A class X1.5 flare started on the solar limb at 00:43 UT on 21 April 2002, which was associated with a CME observed at 01:27 UT by LASCO C2. The coordinated analyses of this flare include TRACE 195 Å images and SUMER spectra in lines of Fe XXI, Fe XII, and C II. We find that: 1) The flare began with a jet seen by TRACE, which was detected by SUMER in the C II line as a strong brightening with blue shifts up to 170 km s^-1. At that time only weak emission was detected in Fe XII and Fe XXI. 2) Subsequently, a weak looplike brightening started south of the jet, moving outwards with an average speed of about 150 km s¹. The SUMER spectra responded this moving loop as separatingly brightenings, visible only in the Fe XXI line. The southwards moving component contains red- and blue-shifted emission features and has an apparent speed of ∼ 120 km s¹. The absence of signatures in Fe XII and C II lines indicates that the moving weak loop seen by TRACE corresponds to the emission from very hot plasma, in a blend line in the 195 Å bandpass due to Fe XXIV formed at T > 10 MK. 3) The trigger mechanism of the flare and associated CME can be interpreted in the same way as that proposed by Wang et al. (2002) for an event with similar initial features.