2. Observational data
On February 4, 1995, an eruptive flare (GOES class M2.6) developed in active region NOAA 7834 ( =0.95), in the time interval 15:42-16:39 UT. The maximum H emission occurred at 15:43 UT (Solar Geophysical data).
At the onset of the eruptive flare, Yohkoh was just coming out of its night, so the impulsive phase was observed only with the Wide Band Spectrometer (WBS, Yoshimori et al., 1991) in the energy channels from 20 to 91 keV. Later on during the flare development, the signal was too low to be recorded with this instrument. The Soft X-ray Telescope (SXT, Tsuneta et al., 1991) and the Hard X-ray telescope (HXT, Kosugi et al., 1991) began the observations in flare mode around 15:46 UT, for an interval of about 10 minutes. SXT obtained images (FOV = , /pxl) with the aluminum (Al12) and beryllium (Be119) filters, with a time resolution ranging between 2 and 6 s. The HXT recorded data in Pulse Height Mode (PHM) with 8 s time resolution; we could obtain images only in the lowest energy Lo channel (14-23 keV), due to the low emission in higher energy bands. The HXT images (FOV = , pointing resolution ) were recovered with an integration time of about 50 s and coaligned with SXT images (Masuda, 1994). The coalignment of Yohkoh images with our photospheric and chromospheric observations was obtained using the full disk observations of the Mees White Light Telescope (Wülser, 1996). The Bragg Crystal Spectrometer (BCS, Culhane et al., 1991) recorded spectra in the three channels S XV, Ca XIX and Fe XXV, without spatial resolution, from 15:46 UT up to 15:53 UT. In the following analysis, we will mainly use the Fe XXV data.
For the general description of the available ground based observations we refer to Paper I. We recall that images of the flare region, with filters in different bands, were acquired with the Vacuum Tower Telescope (VTT) at NSO/SP from 15:31 to 16:08 UT, with a typical temporal resolution of few seconds and a spatial resolution of about . Spectra in the range 3750-4150 Å were acquired with the Universal Spectrograph (USG) from 15:43:00 until 15:56:03 UT, with the slit moving on different positions in the FOV. This spectral range contains both the CaII K and H lines, that we use to provide a diagnostic of plasma flows in the chromosphere. Finally, full disk magnetic maps were available from NSO/Kitt Peak after 18:00 UT.
© European Southern Observatory (ESO) 1997
Online publication: March 24, 1998