Variations in p-mode Parameters and Sub-surface Flows of Active Regions with Flare Activity

We examine the characteristic properties of photospheric p-modes and sub-photospheric flows of active regions (ARs) observed during the period of 26-31 October 2003. Using ring diagram analysis of Doppler velocity data obtained from the Global Oscillations Network Group (GONG), we have found that p-mode parameters evolve with ARs and show a strong association with flare activity. Sub-photospheric flows, derived using inversions of p-modes, show strong twist at the locations of ARs, and large variation with flare activity.Comment: 7 pages, 3 figures, to be appear in the ASI Conference Serie

A Technique for Automated Determination of Flare-ribbon Separation and Energy Release

We present a technique for automatic determination of flare-ribbon separation and the energy released during the course of two-ribbon flares. We have used chromospheric H$\alpha$ filtergrams and photospheric line-of-sight magnetograms to analyse flare-ribbon separation and magnetic-field structures, respectively. Flare-ribbons were first enhanced and then extracted by the technique of "region growing", i.e., a morphological operator to help resolve the flare-ribbons. Separation of flare-ribbons was then estimated from magnetic polarity reversal line using an automatic technique implemented into Interactive Data Language (IDL\tm) platform. Finally, the rate of flare-energy release was calculated using photospheric magnetic-field data and the corresponding separation of the chromospheric H$\alpha$ flare-ribbons. This method could be applied to measure the motion of any feature of interest (e.g., intensity, magnetic, Doppler) from a given point of reference.Comment: 20 pages, 7 figure

Activity Related Variations of High-Degree p-Mode Amplitude, Width and Energy in Solar Active Regions

We study the properties of high degree p-mode oscillations in flaring and dormant ARs and compare them with those in corresponding quiet regions (QRs) to find the association of mode parameters with magnetic and flare related activities. Our analysis of several flaring and dormant ARs, showed strong association of mode amplitude, width and energy with magnetic and flare activities although their changes are combined effects of foreshortening, filling factor, magnetic activity, flare activity, and measurement uncertainties. We find that the largest decrease in mode amplitude and background power of an AR are caused by the angular distance of the AR from the solar disc centre. After correcting the mode parameters for foreshortening and filling factor, we find that the mode amplitude of flaring and dormant ARs are smaller than in corresponding QRs, and decreases with increasing MAI suggesting a larger mode power suppression in ARs with stronger magnetic fields. The mode widths in ARs are larger than in corresponding QRs and increase with MAI, indicating shorter lifetimes of modes in ARs than in QRs. The largest decrease (increase) in mode amplitude (mode width) of dormant ARs is found in the five minute frequency band. The average mode energy of both the flaring and dormant ARs are smaller than in their corresponding QRs, decreasing with increasing MAI. But the average mode energy decrease rate in flaring ARs are smaller than in dormant ARs. Also, the increase in mode width rate in dormant (flaring) ARs is followed by decrease (increase) in amplitude variation rate. Furthermore, inclusion of mode corrections for MAI shows that mode amplitude and mode energy of flaring ARs increase with FI while mode width shows an opposite trend. The increase (decrease) in mode amplitude (width) is larger in the five minute and higher frequency band. Increase in width variation rate is ..

Magnetic structure of solar active region NOAA 11158

Magnetic fields in the solar corona are responsible for a wide range of phenomena. However, any direct measurements of the coronal magnetic fields are very difficult due to lack of suitable spectral lines, weak magnetic fields, and high temperatures. Therefore, one extrapolates photospheric field measurements into the corona. Owing to low coronal plasma $\beta$, we can apply a force-free model in lowest order to study the slow evolution of active region (AR) magnetic fields. On applying these models to AR 11158 and compared with coronal plasma tracers, we found that (1) the approximation of potential field to coronal structures over large length scales is a reasonable one, 2) linear force-free (LFF) assumption to AR coronal fields may not be applicable model as it assumes uniform twist over the entire AR, and 3) for modeling fields at sheared, stressed locations where energy release in the form of flares are usually observed, non-linear force free fields (NLFFF) seem to provide a good approximation. The maximum available free-energy profile shows step-wise decrease that is sufficient to power an M-class flare as observed.Comment: To appear in BASI 2013, Bulletin of Astronomical Society of Indi

Filament Eruption in NOAA 11093 Leading to a Two-Ribbon M1 Class Flare and CME

We present multi-wavelength analysis of an eruption event that occurred in Active Region (AR) NOAA 11093 on 7 August 2010, using data obtained from SDO, STEREO, RHESSI and GONG H$\alpha$ network telescope. From these observations, we inferred that upward slow rising motion of an inverse S-shaped filament lying along the polarity inversion line (PIL) resulted in a CME subsequent to a two-ribbon flare. Interaction of overlying field line across the filament with side lobe field lines, associated EUV brightening, and flux emergence/cancellation around the filament were the observational signatures of the processes leading to its destabilization and the onset of eruption. Moreover, the rising motion profile of filament/flux rope corresponded well with flare characteristics, viz., the reconnection rate and HXR emission profiles. Flux rope accelerated to the maximum velocities as a CME at the peak phase of the flare, followed by deceleration to an average velocity of 590 kms$^{-1}$. We suggest that the observed emergence/cancellation of magnetic fluxes near the filament caused it to rise, resulting in the tethers to cut and reconnection to take place beneath the filament; in agreement with the tether cutting model. The corresponding increase/decrease in positive/negative photospheric fluxes found in the post-peak phase of the eruption provides unambiguous evidence of reconnection as a consequence of tether cutting.Comment: 19 Pages, 9 figures, Submitted in Solar Physic

On the injection of helicity by shearing motion of fluxes in relation to Flares and CMEs

An investigation of helicity injection by photospheric shear motions is carried out for two active regions(ARs), NOAA 11158 and 11166, using line-of-sight magnetic field observations obtained from the Helioseismic and Magnetic Imager on-board Solar Dynamics Observatory. We derived the horizontal velocities in the active regions from the Differential Affine Velocity Estimator(DAVE) technique. Persistent strong shear motions at the maximum velocities in the range of 0.6--0.9km/s along the magnetic polarity inversion line and outward flows from the peripheral regions of the sunspots were observed in the two active regions. The helicities injected in NOAA 11158 and 11166 during their six days' evolution period were estimated as $14.16\times10^{42}$Mx$^2$ and $9.5\times10^{42}$Mx$^2$, respectively. The estimated injection rates decreased up to 13% by increasing the time interval between the magnetograms from 12 min to 36 min, and increased up to 9% by decreasing the DAVE window size from $21\times18$ to $9\times6$ pixel$^2$, resulting in 10% variation in the accumulated helicity. In both ARs, the flare prone regions (R2) had inhomogeneous helicity flux distribution with mixed helicities of both signs and that of CME prone regions had almost homogeneous distribution of helicity flux dominated by single sign. The temporal profiles of helicity injection showed impulsive variations during some flares/CMEs due to negative helicity injection into the dominant region of positive helicity flux. A quantitative analysis reveals a marginally significant association of helicity flux with CMEs but not flares in AR 11158, while for the AR 11166, we found marginally significant association of helicity flux with flares but not CMEs, providing evidences of the role of helicity injection at localized sites of the events.Comment: In press, Ap

Seismic investigation of the solar structure using GONG frequencies

Using the recently obtained GONG frequencies, we investigate the properties of the solar interior by constructing solar models with various input physics like opacities, equation of state, nuclear reaction rates etc. The differential asymptotic inversion technique is then used to infer the relative difference in sound speed between the Sun and solar models. Here we apply these results to test equation of state and different formulation for calculating the convective flux.Comment: Latex, 2 pages, 3 figures, To appear in the IAU Symp. # 181: "Sounding solar and stellar interiors", eds. F.X. Schmider & J. Provos

Variations in pp-Mode Parameters with Changing Onset-Time of a Large Flare

It is expected that energetic solar flares releasing large amount of energy at the photosphere may be able to excite the acoustic ($p$-) modes of oscillations. We have determined the characteristic properties of mode parameters by applying the ring diagram technique to 3-D power spectra obtained for solar active region NOAA 10486 during the long duration energetic X17.2/4B flare of October 28, 2003. Strong evidence of substantial increase in mode amplitude and systematic variations in sub-surface flows, i.e., meridional and zonal components of velocity, kinetic helicity, vorticity, is found from comparison of the pre- to the post-flare phases.Comment: 14 pages, 4 figure

Transient Magnetic and Doppler Features Related to the White-light Flares in NOAA 10486

Rapidly moving transient features have been detected in magnetic and Doppler images of super-active region NOAA 10486 during the X17/4B flare of 28 October 2003 and the X10/2B flare of 29 October 2003. Both these flares were extremely energetic white-light events. The transient features appeared during impulsive phases of the flares and moved with speeds ranging from 30 to 50 km s$^{-1}$. These features were located near the previously reported compact acoustic \cite{Donea05} and seismic sources \cite{Zharkova07}. We examine the origin of these features and their relationship with various aspects of the flares, {\it viz.}, hard X-ray emission sources and flare kernels observed at different layers - (i) photosphere (white-light continuum), (ii) chromosphere (H$\alpha$ 6563\AA), (iii) temperature minimum region (UV 1600\AA), and (iv) transition region (UV 284\AA).Comment: 26 pages, 13 figures, 2 tables, accepted for publication in Solar Physic