Solar Cycle 24 Group E
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I was not present for the gamma-ray talks as I was giving a talk myself in the microflare session. | I was not present for the gamma-ray talks as I was giving a talk myself in the microflare session. | ||
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Latest revision as of 17:40, 18 January 2010
Milligan notes
Tuesday
Shaun Bloomfield: Flare Prediction
Work in progress. Just got funded. Begins in new year.
Larger flares occur on the decay phase of solar cycle.
Bayesian probability of flare producing active region given prior knowledge of flare production rate for given active region class.
GOES X-ray events catalog, EUV images (for flare location), PROBA2/SWAP, NOAA/SWPC AR summary, SOHO/MDI magnetograms.
Flare forecast ultimately to be used on www.solarmonitor.org
Ryan Milligan: GOES Flare Statistics over 3 Solar Cycles
Describes previous statistical analyses of solar flares.
How a GOES event is described.
Background subtraction technique and temperature and emission measure calculations.
Derived relationships between flare plasma parameters and GOES class.
Time delay between peak temperature and peak in emission measure is a indicator of loop filling times. More impulsive events have faster filling times.
Background subtraction may have an effect on temperature values. Needs further work.
Marina Battaglia: Pre-flares Observed By RHESSI
Describes the standard flare model.
Gordon Hurford points out that logarithmically increasing emission needs to be interpreted carefully.
Assume, T, EM and N_e increase before HXR emission begins - chromospheric evaporation, but no HXRs --> thermal conduction.
Compares beam driven and conductive heating. Heat flux saturation.
Result: pre-HXR emission density increases can be explained by conduction driven evaporation.
Lyndsay Fletcher: Chromospheric Flares
Diagnose flare input from chromospheric signatures.
Flare wave energy transport in the chromosphere.
Can you use WL images to confine the electron population from RHESSI? Total energy input?
Can we assume a static (VAL) model of chromosphere?
Modes of energy transport: particles versus waves, acceleration of particles in the chromosphere versus corona.
MHD simulations including Poynting Flux.
What happens to a strong Alfven wave pulse in the chromosphere?
Ryan Milligan: Velocity Characteristics of Evaporated Plasma Using Hinode/EIS
Describe standard chromospheric evaporation cartoon.
Previous observational studies and their limitations.
Event observed by EIS and RHESSI in 12 ionization stages of Fe.
Upflow velocity was found to be dependent on temperature.
During the impulsive phase the bulk of the Fe XXIII and Fe XXIV emission was found to be stationary at the footpoints.
K. Watanabe: Production of High Temperature Plasma in a Flare
Shows that Fe XXIII emission is completely blueshifted early in the impulsive phase.
Multiple footpoint observations.
3 EIS rasters during impulsive phase.
DEM analysis for 17 emission lines.
Fe XXIII and Fe XXIV temperature diagnostics.
Density variations as a function of time.
T. Watanabe: White Light Flares with SOT
Strongest G-band emission came from same location as WL and HXR emission.
G-band emission from photosphere, but 50-100 keV electrons cannot reach photosphere, only chromosphere. >900 keV need to reach photosphere.
Wednesday
Haisheng Ji: Magnetic Reconnection Between Sheared Flux Ropes
Describes the sigmoid -> arcade transitionof HXR emission from RHESSI.
Sigmoid phase: footpoints move along ribbon.
Arcade phase: footpoints separate.
Shen et al. 2008: different energies appear 'mixed' in terms of height during loop contraction, but during the expansion phase, higher energy emission clearly comes from higher altitudes.
Wei Lui: Conjugate HXR Footpoints During an X10 Flare
Describes footpoint motion during sigmoid phase of X10 event - antiparallel to neutral line initially, then parallel later on.
Rapid decrease of footpoint shear cotemporal with downward motion of looptop.
Mentions early downward moving looptop source, possible interpretation: shock heating, loop shrinkage.
Asymmetric footpoint HXR fluxes due ot magnetic mirroring. Bright footpoint corresponds to region of weak B field, and vice versa. But not all the time!
Brighter footpoint has slightly harder spectral index.
Does column density affect spectral index? maybe, when combined with mirroring.
Jim McTiernan: DEM Measurements Using RHESSI
DEM is estimated by N-element power law.
Keep adding power laws to DEM curve until reduced chi^2 is minimized.
Try to constrain nonthermal break energy at lower energies. Vary break until chi^2 is minimized. Can give large range of acceptable values (22-39 keV)
It is possible to obtain DEM using RHESSI and GOES data while taking nonthermal emission into account.
Yang Su: Spectral Breaks in HXR Flare Spectra
Importance of spectral break between single and double power law in HXR spectra.
Can non-uniform ionization explain the spectral break? Not alone, must be other factors.
Investigate the effect of a step versus linear change in ionization fraction of target.
Eduard Kontar: X-ray Emission/Electron Visibilities
From visibilities, electron images appear smaller at higher energies.
Can infer the height and FWHM of magnetic flux tube from electron images.
Source shape is dependent on reconstruction algorithm - more eccentric at higher energies.
Size of footpoint decrease with energy suggesting strong horizontal magnetic field at 900 km. Flux tube decrease sharply with height.
Pascal Saint-Hilare: X-Ray Emission From a Current Sheet in the Wake of a CME
Motivated by work by Bemporand (2006). LDE with hot plasma for 2.3 days.
Combinations of spatially integrated, imaging spectroscopy and visibilities revealed purely thermal source at high altitude. Not powered by accelerated particles.
Plasma at both 1.3 and 1.7 R_Sun were both 8 MK. Can be heated using 4% of RHESSI energy.
Determines a temperature scale height of 25", emission measure scale height = 4".
More work needed on energy displacement.
Lindsay Glesner & Sam Krucker: Coronal HXR Sources
Description and reason for studying occulted events.
Coronal densities too low to produce HXRs (<10^9 cm^-3).
Number of accelerated electrons must be the of the same order as nonthermal electrons.
Above the looptop source is entirely nonthermal and IS the acceleration region.
Critical that Hinode remains on AR target a day after M-flare producing AR becomes occulted, or 3 days after X-classes. Good when compared with STEREO-A.
Thursday
I was not present for the gamma-ray talks as I was giving a talk myself in the microflare session.
