Flares V
Presiding: G Emslie, Oklahoma State University; J M McTiernan, Space Sciences Laboratory, University of California, Berkeley
SP51C-01 08:30h
Dissertation Talk: High Resolution Observations of Multi-Wavelength Emissions During Two X-Class White-Light Flares
We observed two X-class white-light flares (WLF) on 2003 October~29 (~20:40~UT) and November~2 (~17:16 UT) using the Dunn Solar Telescope (DST) and its High-Order Adaptive Optics (HOAO) system in several wavelengths. The spatial resolution was close to the diffraction limit of DST's 76~cm aperture. The temporal resolution was as high as 2~s. It is the first time that WLFs were observed in the Near Infrared (NIR) wavelength region. We present a detailed study in this presentation by comparing the photospheric continuum observations during these two events with corresponding line-of-sight (LOS) magnetograms of the Michelson Doppler Imager (MDI) and hard X-ray (HXR) data of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Our observations show that: Significant intensity enhancements were observed in the visible and NIR continua and G-band during the impulsive phase of the flares. The maximum intensity enhancements were 37% of white-light and 25% of the NIR continuum during the first event, and 76% of white-light and 66% of the NIR continuum for the second flare. The flares were typical two ribbon flares. All ribbons showed a brighter core surrounded by a halo structure. The ribbon separation speeds were about 28~km/s in the first and 24~km/s in the second event based on NIR observations. The derived electric fields in the reconnection current sheet Ec are about 23~V~ cm-1 and 22~V~cm-1, respectively. The NIR emission and the impulsive HXR emission up to 800~keV were well correlated, not considering a small delay of less than two minutes. The high resolution and high cadence images gave us the first chance to measure the cooling time of flares close to the photosphere. We found that the cooling process could be characterized by two steps. A quick temperature drop, which is related to the cooling process of the bright cores, and a relative slow decay related to the halo structures. The fine scale is in the order of less than 30~s and a few minutes for these two steps, respectively. Based on these observational results, we discuss several models that provide possible mechanisms to explain these continuum enhancements, especially in the NIR. This work is supported by NSF under grants ATM-0313591, ATM-0236945, ATM-0233931 and AST-0307676, by NASA under grants NAG5-10910, NAG5-10212 and NAG5-12733, and by Air Force under grant F49620-02-1-0265 and by NSFC-10103004.
SP51C-02 09:00h
Large-scale Activities in the 2003 October 29 Flare
We present a multiwavelength study of the 2003 October 29 X10 Flare using the data from Improved Solar Observing Optical Network (ISOON), the Solar and Heliospheric Observatory (SOHO), Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Transition Region and Coronal Explorer (TRACE), and Owens Valley Solar Array (OVSA). Our study is focused on the large-scale, post-eruption activity on the Sun associated with CMEs, whereas other existing studies are concentrated on the flare core region. In specific, we found two extended remote brightenings and coronal dimmings observed at H-alpha (ISOON) and at extreme ultraviolet (SOHO/EIT) wavelengths, respectively, which are more than 3× 105 km away from the main flare site. These remote H-alpha brightenings are located on the edge of coronal holes that showed dimming after the flare. We consider it unlikely that the remote brightenings are produced by Moreton waves, because they are almost simultaneous with the main flare emissions observed at hard X-ray and microwave wavelengths. We suggest that they rather represent heating of the chromosphere by the flare-accelerated electrons traveling along the large-scale magnetic loops connecting the flare core to the remote patches. We examine the relationship between the HXR footpoint motions in the flare core and the dynamics of the remote patches in order to explore the large-scale magnetic reconfiguration that is responsible for the flare and CME.
SP51C-03 09:15h
TRACE and RHESSI observations of white-light flares
TRACE gives a photometrically stable, high-resolution view of the visible and UV emissions of solar flares, with enough diagnostic power to distinguish photospheric from chromospheric contributions. These emissions dominate the radiant energy of a flare and correspond well with hard X-ray emission in the impulsive phase. We survey these data with reference to well-observed events of 4~October~2002 and 4~November~2003, on the disk (M4; S19W09) and on the limb (X17; S19W83) respectively. We analyze the spatial and temporal properties of the footpoint sources in these two events, characterizing their physical parameters (contrast, image gradients, apparent motions). The brightest kernels of the 4~October~2002 event have intensities twice that of the quiet photosphere, and have sizes close to the Nyquist limit of the TRACE pixels (0.5~arc~sec). The white-light footpoint sources can be considered as a proxy for the target region of fast electrons studied via hard X-ray bremsstrahlung. We compare RHESSI hard X-ray footpoint sources with their white-light counterparts and estimate filling factors for the hard X-ray emission itself.
SP51C-04 09:30h
A Search for the Relationship Between Subphotospheric Dynamics of Active Regions and Flaring Activity
MHD models of solar flares and CMEs suggest the magnetic energy for these events can be accumulated and released in magnetic structures sheared and twisted by plasma motions. We use time-distance helioseismology for investigating subphotospheric structures and dynamics of active regions that might be related to their flaring activity. In particular, we present a detailed study of active region NOAA 10486, which produced a series of X-class flares, during its passage on the solar disk for 8 days, Oct.25-Nov.1, 2003. The maps of subsurface flows and sound-speed perturbations are obtained from the SOHO/MDI data every 2-hours during this period, with 8-hour resolution and for the depth range of 0-12 Mm, and compared with the MDI magnetograms and X-ray data from RHESSI and GOES. The results reveal interesting dynamics at the depth of 4-6 Mm, which is compared with the restructuring, emergence and cancellation the magnetic field in this region.
SP51C-05 09:45h
On the Relation Between Flow Fields and Magnetic Field Evolution in Flare Productive NOAA Active Region 10486
We present high resolution observations of flow fields within solar NOAA active region 10486 before an X10 flare on October 29, 2003. From 2003 October 28 to November 4, a complex Δ-sunspot located in NOAA 10486 produced dramatic flare activities in the descending phase of the solar cycle 23. The flow fields are measured by local correlation tracking (LCT) based on speckle masking white-light images, near-infrared (NIR) continuum images at 1.56 Μm, and G-band images obtained with the Dunn Solar Telescope (DST) of the National Solar Observatory/Sacramento Peak (NSO/SP). NSO's newly developed high-order adaptive optics system at the DST was used to achieve diffraction-limited imaging with a high signal-to-noise ratio. The spatial resolution of the images approaches the diffraction limit of the 76 cm aperture DST of about 0.14 ″ at 527 nm. In addtion, we use longitudinal magnetograms from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SoHO) to study the evolution of photospheric magnetic field and its correlation with flow fields in this flare productive active region. We link strong magnetic shear and fast emergence of magnetic flux to photospheric flows, which might trigger the flares. Our result suggests that the time-series analysis of the photospheric flow fields is a critical observational diagnostic for the evolution of magnetic fields in solar active regions. This work was supported by NSF under grant ATM 03-42560, ATM 03-13591, ATM 02-36945, and MRI AST 00-79482 and by NASA under grant NAG 5-13661.