Flares II Posters
Presiding: J Zhang, George Mason University; S P Plunkett, Naval Research Laboratory
SP23B-01 1330h
Magnetic Helicity Change Rate Associated with an X10 White-Light Flare
Solar active region NOAA 10486 was very active during the descending phase of solar cycle 23. Eight X-class flares and a multitude of M-class flares were observed in this region from 2003 October 23 to November 6. In our previous study we presented the high resolution observations of the flow fields associated with the X10 white-light flare in this active region on 2003 October 29. We linked the strong photospheric shear flow with the flare. In this paper, we further our study by investigating the magnetic helicity injection rate of the active region NOAA 10486 covering the time period of this X10 white-light flare. The magnetic helicity injection rate due to horizontal photospheric motions is determined by analyzing a set of 1 minute cadence full-disk magnetograms taken by the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, in addition to the flow fields derived previously. The results of this study will aid us to understand the process of energy build-up and release associated with the flare.
SP23B-02 1330h
High Resolution Chromospheric Flow Fields in Solar Active Region NOAA 9393 Before and After an X20 Flare
Hα full-disk images of the Sun obtained at the Big Bear Solar Observatory (BBSO) are used to measure the chromospheric flow field before and after the X20 flare in solar active region NOAA 9393 on April 2, 2001. Local correlation tracking is used to determine global (differential rotation) and local flow fields (flows in active regions and filaments). We present high-resolution (2k × 2k pixel) flow maps to analyze the dynamics of the chromosphere before and after the flare. If there is a typical pattern in the motions of a flaring active region, it can be used to predict flare activity and/or the onset of Coronal Mass Ejections (CMEs). The high quality of the limb-darkening corrected and contrast-enhanced Hα full-disk images make them an ideal data set for these types of studies due to their high-temporal resolution (1-minute cadence) and extended coverage (more than 500 filtergrams).
http://www.bbso.njit.edu
SP23B-03 1330h
Converging motions of solar flare ribbons
We present a number of examples of solar flares, in which conjugate ribbons move toward each other during the impulsive phase. Meanwhile, HXR coronal sources move down. Normal separation motions occur only after the impulsive phase. This phenomena may pose a new topic to flare reconnection theory.
SP23B-04 1330h
The Characteristics of Hard X-ray Production in Flares Driven by Filament Eruptions
We investigate the temporal and spatial relationship between filament eruptions and the production of hard X-ray emission using spatially resolved high cadence data from TRACE and RHESSI. In particular, we focus on comparing the characteristics of the hard X-ray production in `successful' and `failed' filament eruption cases. Our preliminary findings indicate even failed eruption events can generate significant energy release and hard X-ray emission with the hard X-ray production apparently correlated to the rate of expansion of the filament. The spatial distribution of the hard X-ray emission, while depending upon the overall strength of the event, also depends on the evolutionary behavior of the filament as it erupts, e.g. loop-like versus "zipper"-like.
SP23B-05 1330h
On the cooling processes of solar flare loops in the gradual decaying phase---Suppression of conduction and heating by plasma wave turbulence
High spectral and spatial resolution observations of RHESSI show that emission in the gradual phase of many solar flares is dominated by a thermal looptop source, which cools down faster than expected from the radiative cooling but much slower than that due to the cooling by classical Spitzer conductivity. This could be due to a continuous energy input at a rate equal to the conduction rate. One would then expect a nearly isothermal loop with an almost uniform emission along the loop and significant energy injections at the foot points. However, the looptop image is resolved along the loop and appears to be confined to the top portion of the loop. This requires a suppression of conduction within the source region. Combining imaging spectroscopic observations of RHESSI with the GOES light curves, we model the evolution of the loops in the gradual phase of several flares. We find that the suppression of conduction alone can not account for the RHESSI observations in a quasi-steady equilibrium loop model. A sustained (although declining) energy input is also needed. Thermal damping of turbulence produced continuously (albeit at a declining rate) during the decay phase can be responsible for the heating process. Presence of turbulence could also suppress the conduction rate. This work is supported by NASA grants NAG5-12111, NAG5 11918-1, and NSF grant ATM-0312344.
http://www.stanford.edu/~~arjiang/work.html
SP23B-06 1330h
The Relationship Between Active Region Twist & Solar Flaring Activity
Twisted magnetic field lines in solar active regions constitute stressed flux systems -- the reconnection of which can release the stored (excess) energy in the form of solar flares. The explosive release of energy through such flares, beyond contributing to the heating of the solar corona, can sometimes affect the near-Earth Space environment and trigger geomagnetic storms. Here we explore the relationship between solar flares and the pre-flare magnetic topology (characterized by the twist α in the magnetic fields lines) of the active regions in which the flares originate. We have discovered that flares are preferentially initiated in sub-regions that have an high gradient in twist and lie close to chirality inversion lines (which separate regions with twist of opposite handedness). Our results imply that the topology of magnetic field lines -- as characterized by the twist parameter α -- plays an important role in magnetic reconnection and flaring events.
SP23B-07 1330h
Reconciling Hydrodynamic Simulations With Yohkoh and RHESSI Observations of Solar Flares
High spatial resolution TRACE observations provide compelling observational evidence for small-scale filamentation in solar flares. In this poster we present results from time-dependent hydrodynamic simulations that treat a flare as a succession of independently heated filaments. The energy deposited onto each filament and the volume of each filament are derived from the observed GOES soft X-ray fluxes. These numerical simulations are able to reproduce both the evolution of the line intensity and the shape of the line profile for the Yohkoh BCS Ca XIX and S XV lines. Of particular significance is the fact that the simulated line profiles are always dominated by the stationary component, consistent with observations. In this model the strongly blueshifted emission evident during the initial heating of a thread is largely masked by emission from threads that have been heated previously and do not show bulk motions. In addition to comparisons with Yohkoh we will also present detailed comparisons between simulation results and RHESSI flare observations.
SP23B-08 1330h
Si XII X-ray Satellite Lines in Solar Flare Spectra
We demonstrate the temperature dependence of the intensity ratio of dielectronic satellite lines due to Li-like Si (Si XII) to nearby He-like Si (Si XIII) 1s2 - 1snp(n=3, 4, 5) lines emitted in solar flare X-ray spectra. These lines, which occur in the wavelength range 5.253~Å--5.818~Å, have been observed by the RESIK bent crystal spectrometer on the Russian CORONAS-F solar mission. Line features made up of several strong satellites with transitions 1s2 n'l' - 1s n'l' nl lie near the `parent' Si XIII lines, transition 1s2 1S0 - 1snp 1P1; thus, the feature at 5.818~Å is made up of several blended Si XII satellites with `spectator' electrons n'l'=2s or 2p and nl=3p or 3d, and lies on the long-wavelength side of the Si XIII 1s2 - 1s3p line at 5.681~Å. A similar n=4 satellite feature at 5.565~Å is on the long-wavelength side of the Si XIII 1s2 - 1s4p line at 5.384~Å. The Si XII satellites are formed by dielectronic recombination and direct (inner-shell) excitation. The ratio Is/IHe (Is = Si XII satellite line flux, IHe = Si XIII line flux) depends on electron temperature approximately as Te-1. The atomic data needed to calculate Is/IHe for individual n=3 and n=4 Si XII satellite lines have been calculated and will be presented in this paper; excitation mechanisms including those by dielectronic recombination and inner-shell excitation were included using the SUPERSTRUCTURE and Distorted Wave formalisms. With these and theoretical fluxes of the Si XIII lines, synthetic spectra were calculated and compared with RESIK solar flare spectra. Values of Is/IHe measured from RESIK spectra during the decay of four long-duration solar flares, together with temperatures estimated both from the ratio of the GOES channels and from the ratio of total fluxes in two of the four RESIK channels, enable a comparison to be made with theoretical curves. The agreement with the theoretical curve based on synthetic spectra is within expected uncertainties, and the Te-1 dependence is confirmed. Satellites for other Li-like ions are expected to have a similar temperature sensitivity, in particular the Li-like Fe satellites near He-like Fe lines. Although these lines have not been seen with high-resolution spectrometers, the RHESSI mission observes the whole complex during solar flares as the so-called Fe/Ni line feature; addition of these satellites to theoretical spectra from the CHIANTI code have reduced a long-standing discrepancy with intensities observed by RHESSI. KJHP acknowledges an NRC Research Associateship, and JS and BS acknowledge support from grants (2.P03D.002.22 and PBZ-KBN-054/P03/2001) of the Polish Committee for Scientific Research. RESIK is a joint project between NRL (USA), MSSL, and RAL (UK), IZMIRAN (Russia), and SRC (Poland). The CORONAS-F mission is led by the IZMIRAN Institute.
SP23B-09 1330h
A Generalized Framework For Combining Statistical Measures of Flare Likelihood
There are many parameters which have been found to have varying degrees of correlation with solar flares. We present a framework for combining multiple sources of predictive information to produce a single likelihood value for flare occurrence. The framework is intended as a development tool for flare prediction studies and makes use of the Collaborative Sun-Earth Connector (CoSEC).