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Joshi A.D.,Udaipur Solar Observatory Physical Research Laboratory | Srivastava N.,Udaipur Solar Observatory Physical Research Laboratory
Astrophysical Journal | Year: 2011

We employ a three-dimensional (3D) reconstruction technique for the first time to study the kinematics of six coronal mass ejections (CMEs), using images obtained from the COR1 and COR2 coronagraphs on board the twin STEREO spacecraft, and also the eruptive prominences (EPs) associated with three of them using images from the Extreme UltraViolet Imager. A feature in the EPs and leading edges (LEs) of all the CMEs was identified and tracked in images from the two spacecraft, and a stereoscopic reconstruction technique was used to determine the 3D coordinates of these features. True velocity and acceleration were determined from the temporal evolution of the true height of the CME features. Our study of the kinematics of the CMEs in 3D reveals that the CME LE undergoes maximum acceleration typically below 2 R ⊙. The acceleration profiles of CMEs associated with flares and prominences exhibit different behaviors. While the CMEs not associated with prominences show a bimodal acceleration profile, those associated with prominences do not. Two of the three associated prominences in the study show a high and increasing value of acceleration up to a distance of almost 4 R ⊙, but acceleration of the corresponding CME LE does not show the same behavior, suggesting that the two may not be always driven by the same mechanism. One of the CMEs, although associated with a C-class flare, showed unusually high acceleration of over 1500 m s-2. Our results therefore suggest that only the flare-associated CMEs undergo residual acceleration, which indicates that the flux injection theoretical model holds well for the flare-associated CMEs, but a different mechanism should be considered for EP-associated CMEs. © 2011. The American Astronomical Society. All rights reserved.

Maurya R.A.,Udaipur Solar Observatory Physical Research Laboratory | Ambastha A.,Udaipur Solar Observatory Physical Research Laboratory
Solar Physics | Year: 2010

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 Hα 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 the magnetic-polarity reversal line using an automatic technique implemented into an 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 Hα 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. © Springer Science+Business Media B.V. 2010.

Vemareddy P.,Udaipur Solar Observatory Physical Research Laboratory | Maurya R.A.,Udaipur Solar Observatory Physical Research Laboratory | Ambastha A.,Udaipur Solar Observatory Physical Research Laboratory
Solar Physics | Year: 2012

We present a multi-wavelength analysis of an eruption event that occurred in active region NOAA 11093 on 7 August 2010, using data obtained from SDO, STEREO, RHESSI, and the GONG Hα network telescope. From these observations, we inferred that an upward slow rising motion of an inverse S-shaped filament lying along the polarity inversion line resulted in a CME subsequent to a two-ribbon flare. Interaction of overlying field lines across the filament with the side-lobe field lines, associated EUV brightening, and flux emergence/cancelation around the filament were the observational signatures of the processes leading to its destabilization and the onset of eruption. Moreover, the time profile of the rising motion of the filament/flux rope corresponded well with flare characteristics, viz., the reconnection rate and hard X-ray emission profiles. The flux rope was accelerated to the maximum velocity as a CME at the peak phase of the flare, followed by deceleration to an average velocity of 590 km s -1. We suggest that the observed emergence/cancelation 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. © 2011 Springer Science+Business Media B.V.

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