The Gradual Phase of the X17 Flare on October 28, 2003

Abstract

We present SOHO/CDS observations taken during the gradual phase of the X17 flare that occurred on October 28, 2003. The CDS data are supplemented with TRACE and ground-based observations. The spectral observations allow us to determine velocities from the Doppler shifts measured in the flare loops and in the two ribbon kernels, one hour and a half after the flare peak. Strong downflows (>70 km s^-1) are observed along the loop legs at transition-region temperatures. The velocities are close to those expected for free fall. Observations and results from a hydrodynamic simulation are consistent with the heating taking place for a short time near the top of the arcade. Slight upflows are observed in the outer edges of the ribbons (<60 km s^-1) in the EUV lines formed at log T < 6.3. These flows could correspond to the so-called “gentle evaporation.” At “flare” temperatures (Fe xix, log T = 6.9), no appreciable flows are observed. The observations are consistent with the general standard reconnection models for two-ribbons flares.