TRACE/SXT/SoHO JOP #113 Received: October 13, 1999 Title: The triggering and evolution of Solar Flares Authors: David Alexander (alexander@lmsal.com) Tom Metcalf (metcalf@lmsal.com) Jake Wolfson (wolfson@lmsal.com) Lyndsay Fletcher(fletcher@lmsal.com) We propose a JOP to study the three phases of solar flares, using high cadence, high resolution, multi-thermal imaging from Yohkoh/SXT, and TRACE, and spectral measurements from SoHO/SUMER, SoHO/CDS. The priority in this JOP is image cadence, and as such, field-of-view will be sacrificed where necessary. Scheduling considerations: The JOP is split into three parts, each of which has a different, but related, science goal. In an ideal observing run, with many flares, the three parts should run for around 4 days each. However, as the prime objective of the JOP is high-cadence observations of the pre-flare changes and impulsive phase, the first part of the JOP will be run until a flare is observed, if necessary for the entire observing period. Target Selection: Target selection will be made by the SXT Chief Observer. The target will be the brightest active region on the sun, since this is the standard and safest mode of operation for SXT. In this case SXT will automatically take PFI's on the brightest AR (or can alternate images between up to 4 (brightest) ARs). The instrument will only exceptionally be pointed at another region, (e.g., one which is flaring repeatedly). In both cases we hope to stick with the target for a few days, rather than 'flare chase' although the situation will be reassessed by the SXT_CO on a daily basis. If a flare occurs in a region other than the target region, i.e., other than the brightest region on the sun, SXT will by default go to this region for flare observations. This is just bad luck. Observations: Part 1. Preflare study ============== Science goal here is the study of the pre-flare build-up for pre-heating, gentle evaporation etc. using UV, soft X-rays and some hard X-ray information if available. HXT - LOW channel if available - no special observation mode (included for information) SXT - Filters - Al.1/AlMg Pointing - fixed pointing on target selected by SXT CO Duration - Continuously for 4 days Exposures - fixed maximum exposure to avoid problems of not sitting on brightest active region (when applicable) F-O-V - to cover active region - 2X2 PFI (?) Cadence - not an issue Fixed pointing is suggested to make sure that pre-flare data for flare occurring in TRACE f-o-v is obtained. SXT will catch all 'daytime' flares as usual of course. TRACE - Filters - (195 or 171)* and 1600A F-O-V - restricted TRACE f-o-v (384"x384") Cadence - maximum possible with above filter complement Note (*) the EUV filters will be alternated, starting with 195. In other words when the JOP starts, TRACE will run this part of the program with rapid interleaved 195/1600 images until a flare is detected. At the next available opportunity (in practise this will be the next day) the filter will be changed in preparation for the next flare, so that rapid interleaved 171/1600 images will be taken in Part 1. Further, the filter for the impulsive phase study and the filter for the preflare study will be the same, except if the 284 filter is being used for the impulsive phase. In that case, the preflare images will be 195 images Part 2. Impulsive Phase study ===================== Science goal here would be a comparison of EUV and Hard X-rays to study use of UV/EUV as a proxy for energy deposition. HXT - suggest calibration mode to get better energy resolution SXT - Old 'standard' flare table, i.e. not the ejecta flare table (no QR) TRACE - Filter - (171 or 195 or 284)* and 1600 single EUV filter per flare but change filter between flares. EUV and 1600 alternate at high cadence. Priority would be 195-171-284 F-O-V - (384"x384") once flare starts for high cadence Cadence - highest possible Part 3. Gradual Phase study =================== The science goal here is the study of heating and cooling in the gradual phase of flares. Is there an excess thermal energy? How does the flare plasma cool? Is there any sign of upflowing or downflowing material. SXT - Filters - Al.1/AlMg/Be/Al12 (remove thick filters when out of flare mode) Cadence - regular and equal cadence in each filter Exposures - regular AEC F-O-V - 1x1 PFI in flare AND quiet mode We are suggesting a flare table which gives equal weight to each filter. This is not so good for the main phase but will help with the temperature studies in the late phase. Since the gradual phase might include both flare mode and quiet mode data we are suggesting a quiet table which is essentially identical to the flare table but without the thicker filters. TRACE - Filters - 171/195/284 + occasional Lyman-alpha F-O-V - reduced field of view Other Observations: =================== While the main aim of this JOP is to obtain high cadence TRACE and SXT images we welcome the participation of SoHO instruments, on the understanding that the choice of target lies with the SXT CO. SoHO-CDS: Spectroheliograms of target active region in FeXVI, MgX, OV and He1, with a field of view of 240"x240". As high a cadence as the above restrictions allow. Contingencies exist for switching to a line combination involving higher-temperature iron lines, e.g., Fe XIX, if a flare is observed during real-time contact; this would be very desirable for observing flare and post-flare line-shifts. SoHO-SUMER: (if limb target) follow observing sequences outlined in JOP 104 SoHO-MDI: High cadence magnetograms if in hi-res FOV, otherwise whatever MDI is doing at the time.