fl218.plunkett01 Posted: 16-Sep-95 Updated: 07-Jul-96 Events specified: See text
S.P. Plunkett, L.K. Harra-Murnion, K.J.H. Phillips, L. van Driel-Gestztelyi and B. Schmieder
Yohkoh has observed many long duration events (LDEs) to date. This database, combined with ground-based observations, should allow a thorough statistical study of the properties of these interesting events to be carried out for the first time. We have selected the following events for initial study which have durations between 5 and 20 hours, and flare size ranging from C to X GOES class. Several of these events have been studied previously (e.g. Tsuneta 1995, Feldman et al 1995, Schmieder et al, 1995), however these authors did not carry out a comprehensive statistical study involving a large number of events.
21-Feb-92 ~03:00 25-Jun-92 ~06:00 02-Nov-92 ~03:00 13-Nov-92 ~15:00 29-Nov-92 ~08:00 07-May-93 ~21:00 20-Jun-93 ~14:00 01-Nov-93 ~20:00 17-Dec-93 ~20:00
We will use SXT images to examine the morphology of the hot plasma at different stages in the flare development, and will use the filter-ratio method to produce temperature and emission measure maps. We will use HXT data to locate the source(s) of HXR emission relative to the SXR-emitting plasma. We intend to use the pixons method developed by Tom Metcalf for this purpose. We will compare the SXT images to ground-based H-alpha and white light observations to determine the relationship of the structures responsible for emission in the two wavebands. In particular, we are interested in the formation and growth of loops in the decay phase. Among the questions we hope to address using this analysis are: 1) What are the spatial and temporal relationships of the SXR and H-alpha loops? 2) How do the loops develop with time--do they grow continuously as predicted by, for example, the model of Kopp and Pneuman (1976), or do they grow discontinuously as reported by Bruzek (1964)?
We will also use the excellent diagnostic capabilities of the BCS to study the plasma dynamics (non-thermal velocities, upflows etc.) and to determine gross plasma parameters (electron temperature and emission measure) as a function of time for the flares in our sample. Is the evaporation still effective? (Zarro & Lemen, 1988, Schmieder et al 1987)
When the data are analysed, we will compare our results with various existing models of LDEs (e.g. Kopp and Pneuman 1976, Poletto and Kopp 1988, Simnett 1985, Forbes & Malherbe, 1986) to assess their validity and ultimately to address the question of the energy source that maintains the hot plasma at temperatures of several million degrees for many hours.
fl191: 1992 February 21 LDE flare and other LDE flares (Tsuneta)
Abstract of paper to be presented as a poster at the COSPAR conference in Birmingham, U.K. in July 1996.
L.K. Harra-Murnion (Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Surrey RH5 6NT, U.K.) S.P. Plunkett and S.F. Helsdon (University of Birmingham, Birmingham B15 2TT, U.K.) K.J.H. Phillips (Astrophysics Division, Rutherford Appleton Lab., Chilton, Didcot, Oxon., OX11 0QX, U.K.) L. van Driel-Gestztelyi and B. Schmieder (DASOP, Observatoire de Paris, 92195 Meudon Principal Cedex, France)
Yohkoh has observed many long duration events permitting a statistical study of the properties of these interesting events. We have selected 20 flares for analysis which have durations between 5 and 20 hours, and size ranging from C to X GOES class. Employing the Soft X-ray Telescope, the Hard X-ray Telescope and the Bragg Crystal Spectrometer we examine the morphology, temperature, emission measure, location of the hard X-ray source, non-thermal velocities and upflows of the plasma at different stages in the flare development. Our results are used to address the question of the energy source that maintains the hot plasma at temperatures of several million degrees for many hours.