Working group 4: Wednesday AM Membership: Chifor, Mason, Berlicky, Warmuth, Temmer, Bone, Vaananen, Hannah, Battaglia, Ji, Veronig, Milligan, Dennis, Fivian, Fletcher, Hudson Chifor * RHESSI observations of Fe feature at 6.7 keV * Motivations: Morphology, Fe abundances, theory... * Flare sample from LDE late phase for DEM simplicity, eg July 2002 but a sample of about 30 events * GUI plus OSPEX, models typically 3-20 keV isothermal + 2 Gaussians * Interesting background feature (A1) at 7-8 keV, unknown origin * EQW vs T plot for 19-Aug 10:00 based on Chianti 5.0 w/ coronal abundances (some discussion of nature of data/theory fit, if a T dependence maybe it's the ionization balance? Or the isothermality assumption? Or the abundances? Or the Chianti version number) * Much poorer example of 11-Nov-03 flares, comparing A0 (during shutter motions and without), but also in A1 in terms of EQW * Note decreased spectral resolution at high rates Vaananen: how to do abundance estimates with error bars? Hannah microflares * RHESSI microflares: Definitions via Jim McTiernan's flare-finder; complications of event recognition and background determination * Spectral fitting: OSPEX, illustrations from B-class 26-Jun-02 17:18; spectral fits have systematic discrepancies. Dennis: 1/3 keV gain offset problem? * Monte Carlo calibration of OSPEX statistics and biases, using a broad range of (T, em) parameter space: suggests 10^26 ergs non-thermal power as a lower safe limit? Hudson: interesting parameter in thermal/nonthermal ratio Fivian: how to determine dependence on OSPEX starting parameters? Hannah: lots of experimentation in understanding OSPEX nuances Hannah QS * RHESSI quiet Sun: is there a signal when there are no flares at all? * Offpoint modulation technique * Data sampling in 5-minute chunks, binning with roll angle and harmonic analysis * Calibration of technique on known microflares works fine * Results compared with SXR (Pevtsov & Acton 2001) and HXR (Peterson et al. 1966); generally upper limits at high energies but a real signal in the lowest-energy band (3-5 keV) * GOES correlation looks consistent with finite detection @ low energies * Fitting the QS close agreement 5-7 keV (fitted MM spectrum folded into RHESSI response) Vaananen * XSM calibrations with RHESSI and GOES * Ratio of XSM/GOES varies from flare to flare but no corrections for effective temperature * Time-series comparison for 26-Apr-04 event shows discrepancy as reported above * XSM/RHESSI ratios show shutter changes clearly * XSM and MM same PIN supplier * Brian's VGs (see above) on RHESSI calibrations * Larmor radiation, charge and acceleration, model ideas about extracting energy from the solar plasma Mason * Work with Tripathi and Isobe * EIT and H-alpha examples of filament eruption, usual cartoon * Grigis-Benz footpoint tracking: no separation, and why? No filament, one-sided filament, insufficient duration of observations? * Tripathi thesis catalog (2004) => 17 events of which two for detailed analysis * Compare prominence speeds and footpoint motions: parallel motion along ribbons correlates with radial motion of filament in 17 events * 3D cartoons with symmetric/assymetric patterns * Discussion of flux emergence near the PIL Van Driel-Gesztelyi discussion of plausible field distributions to explain different kinds of motion (cf Bogachev & Somov) Milligan * Neupert effect - missing link has been EUV imaging spectroscopy Discussion (Mason, van Driel, Berlicki, Dennis, Hudson...) * CDS plus RHESSI @ HeI 584 ribbon structure => explosive evaporation via upflows (FeXIX) and downflows (HeI) velocities, but hampered by poor time resolution * 2nd flare suggessts gentle evaporation, HeI showing upflows; have 5e9 vs 4e10 ergs/cm^2s * V vs T plots lays it all out nicely. See Mariska et al. or Allred et al for theoretical underpinning Mason: how to calibrate wavelengths? Discussion about resolution limitations Berlicki: similar observations of hot and cool up and down, also in outer edges of ribbons (Oct. 28) Fletcher: momentum balance recalled * Jan. 17 2005 event suggests confusion about HXR and ribbon locations * Aiming at a statistical sample (six flare!) Discussion at length regarding HXR/CDS intercomparisons Temmer * Magnetic constraints for the same flare (X3.8 17 Jan 2005) * RHESSI movie shows mostly two sources, but early on four sources * Good overlay movie with H-alpha showing tendency for HXR at outer edges * Movie of HXR centroids against MDI data - footpoints clearly ignore umbra! Interesting proper motions. * Calculation of reconnection rates vxB - better comparison in negative regions * H-alpha velocity variations, comparison with B and HXR regions * Reconnection rates 5-10x variation consistent with RHESSI dynamic range * Study proper motions considering potential-field connectivity maps vs loop height ranges, up to 100 Mm * Can follow source motion in field geometry consistent with HXR sources * Why does the positive flux not show the reconnection signatures so well? Perhaps jumps of field would happen Fletcher: A jump would still involve flux transfer * Is vxB not always the correct picture?