fl064.pike01 Posted: 17-Aug-92 Updated: 07-Jun-93, 08-Mar-94, 07-Nov-94 Events specified: Flare on 16-Dec-91 at 05 UT
Collaborators: C.D. Pike (ISAS, RAL), J.L. Culhane (MSSL), A. Fludra (MSSL)
A.T. Phillips (MSSL), K.J.H. Phillips (RAL), M. Inda (Tokyo)
T. Watanabe (NAOJ). Other Yohkoh Team members are welcome
to join.
The M2 flare of 05:00 UT 16-Dec-91 appears to be unique amongst the events
observed so far by the BCS. At the outset it shows highly blue-shifted
components in FeXXV, CaXIX and SXV. The velocities observed exceed by several
hundered km/s those observed in any other event (apart maybe from Nov 9). SXT
did not take any images of this event but the HXT data in the low energy
channel show a gradually filling loop structure while the hardest channel
reveals only the two footpoints. This event was also among the first to show
clear evidence of the superhot component in the FeXXVI spectrum. The data
analysed so far suggest that this event may be a singularly good example of
evaporation at work.
Update 07-Nov-94
See Culhane et. al., Solar Physics, 153, 307, 1994. This project is closed with the paper being published.
Update 08-Mar-94
A paper titled ``Yohkoh Observations of the Creation of High Temperature Plasma in the Flare of 16th December 1991'' has been prepared and submitted for publication in
The abstract for this paper is reproduced here.
Yohkoh observations of a impulsive solar flare which occurred on 16 December 1991 are presented. This flare was a GOES M2.7 class event with a simple morphology indicative of a single flaring loop. X-ray images were taken with the Hard X-ray Telescope (HXT) and soft X-ray spectra were obtained with the Bragg Crystal Spectrometer (BCS) on board the satellite. The spectrometer observations were made at high sensitivity from the earliest stages of the flare, are continued throughout the rise and decay phases, and indicate extremely strong blueshifts, accounting for the majority of emission in CaXIX during the initial phase of the flare. The data are compared with observations from other space and ground based instruments. A balance calculation is performed which indicates that the energy contained in non-thermal electrons is sufficient to explain the high temperature plasma which fills the loop. The cooling of this plasma by thermal conduction is independently verified in a manner which indicates that the loop filling factor is close to 100\%. The production of `superhot' plasma in impulsive events is shown to differ in detail from the morphology and mechanisms appropriate for more gradual events.
Update 07-Jun-93
The flare of 16 Dec 1991, an impulsive event, is being analysed using BCS spectra and HXT images. The results of a calculation of the total thermal energy content, based on BCS CaXIX spectra (after Antonucci et al 1982 Sol Phys. 78, 107) were presented recently at a meeting in Japan. HXT images seem to indicate a loop filling process concurrent with large blueshifts observed in BCS CaXIX and FeXXV. This
flare offers strong evidence for chromospheric evaporation processes. Three velocity component fitting is being undertaken at present, to try to determine if there is any superfast component in the initial phase of the flare, correllated with the Hard X-Ray light curve. Papers on this flare, and its support for the chromospheric evaporation model are in preparation.