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Murawski K.,Group of Astrophysics | Srivastava A.K.,Banaras Hindu University | Musielak Z.E.,University of Texas at Arlington | Musielak Z.E.,Kiepenheuer Institute for Solar Physics
Astrophysical Journal | Year: 2014

We present results of three-dimensional (3D) numerical simulations of a fast magnetic twister excited above a foot-point of the potential solar coronal arcade that is embedded in the solar atmosphere with the initial VAL-IIIC temperature profile, which is smoothly extended into the solar corona. With the use of the FLASH code, we solve 3D ideal magnetohydrodynamic equations by specifying a twist in the azimuthal component of magnetic field in the solar chromosphere. The imposed perturbation generates torsional Alfvén waves as well as plasma swirls that reach the other foot-point of the arcade and partially reflect back from the transition region. The two vortex channels are evident in the generated twisted flux-tube with a fragmentation near its apex which results from the initial twist as well as from the morphology of the tube. The numerical results are compared to observational data of plasma motions in a solar prominence. The comparison shows that the numerical results and the data qualitatively agree even though the observed plasma motions occur over comparatively large spatio-temporal scales in the prominence. © 2014. The American Astronomical Society. All rights reserved.. Source


Srivastava A.K.,Aryabhatta Research Institute of Observational science ARIES | Srivastava A.K.,University of Sheffield | Erdelyi R.,University of Sheffield | Murawski K.,Group of Astrophysics | Kumar P.,Astronomy and Space Science Institute KASI
Solar Physics | Year: 2012

Using multi-wavelength observations of Solar and Heliospheric Observatory (SoHO)/Michelson Doppler Imager (MDI), Transition Region and Coronal Explorer (TRACE, 171 Å), and Hα from Culgoora Solar Observatory at Narrabri, Australia, we present a unique observational signature of a propagating supersonic plasma blob before an M6. 2-class solar flare in active region 10808 on 9 September 2005. The blob was observed between 05:27 UT and 05:32 UT with almost a constant shape for the first 2 - 3 min, and thereafter it quickly vanished in the corona. The observed lower-bound speed of the blob is estimated as ≈ 215 km s -1 in its dynamical phase. The evidence of the blob with almost similar shape and velocity concurrent in Hα and TRACE 171 Å images supports its formation by a multi-temperature plasma. The energy release by a recurrent three-dimensional reconnection process via the separator dome below the magnetic null point, between the emerging flux and pre-existing field lines in the lower solar atmosphere, is found to be the driver of a radial velocity pulse outwards that accelerates this plasma blob in the solar atmosphere. In support of identification of the possible driver of the observed eruption, we solve the two-dimensional ideal magnetohydrodynamic equations numerically to simulate the observed supersonic plasma blob. The numerical modelling closely match the observed velocity, evolution of multi-temperature plasma, and quick vanishing of the blob found in the observations. Under typical coronal conditions, such blobs may also carry an energy flux of 7. 0×10 6 erg cm -2 s -1 to balance the coronal losses above active regions. © 2012 Springer Science+Business Media B.V. Source


Srivastava A.K.,Aryabhatta Research Institute of Observational science ARIES | Murawski K.,Group of Astrophysics
Astrophysical Journal | Year: 2012

We observe the motion of cool and hot plasma in a multi-stranded post-flare loop (PFL) system that evolved in the decay phase of a two-ribbon M1.0 class flare in AR 11093 on 2010 August 7 using the Solar Dynamics Observatory/ Atmospheric Imaging Assembly 304 Å and 171 Å filters. The moving intensity feature and its reflected counterpart are observed in the loop system at multiple temperatures. The observed hot counterpart of the plasma probably envelopes the cool confined plasma and moves comparatively faster (∼34kms-1) than the latter (29kms-1) in the form of a spreading intensity feature. The propagating plasma and intensity reflect from the region of another footpoint of the loop. The subsonic speed of the moving plasma and associated intensity feature may be most likely evolved in the PFL system through impulsive flare heating processes. Complementing our observations of moving multi-temperature intensity features in the PFL system and its reflection, we also attempt to solve two-dimensional ideal magnetohydrodynamic equations numerically using the VAL-IIIC atmosphere as an initial condition to simulate the observed plasma dynamics. We consider a localized thermal pulse impulsively generated near one footpoint of the loop system during the flare processes, which is launched along the magnetic field lines at the solar chromosphere. The pulse steepens into a slow shock at higher altitudes while moving along this loop system, which triggers plasma perturbations that closely exhibit the observed plasma dynamics. © 2012 The American Astronomical Society. All rights reserved. Source


Kayshap P.,Aryabhatta Research Institute of Observational science ARIES | Srivastava A.K.,Aryabhatta Research Institute of Observational science ARIES | Murawski K.,Group of Astrophysics
Astrophysical Journal | Year: 2013

We observe a solar surge in NOAA AR11271 using the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly 304 Å image data on 2011 August 25. The surge rises vertically from its origin up to a height of ≈65 Mm with a terminal velocity of ≈100 km s-1, and thereafter falls and fades gradually. The total lifetime of the surge was ≈20 minutes. We also measure the temperature and density distribution of the observed surge during its maximum rise and find an average temperature and a density of 2.0 MK and 4.1 × 109 cm-3, respectively. The temperature map shows the expansion and mixing of cool plasma lagging behind the hot coronal plasma along the surge. Because SDO/HMI temporal image data do not show any detectable evidence of significant photospheric magnetic field cancellation for the formation of the observed surge, we infer that it is probably driven by magnetic-reconnection-generated thermal energy in the lower chromosphere. The radiance (and thus the mass density) oscillations near the base of the surge are also evident, which may be the most likely signature of its formation by a reconnection-generated pulse. In support of the present observational baseline of the triggering of the surge due to chromospheric heating, we devise a numerical model with conceivable implementation of the VAL-C atmosphere and a thermal pulse as an initial trigger. We find that the pulse steepens into a slow shock at higher altitudes which triggers plasma perturbations exhibiting the observed features of the surge, e.g., terminal velocity, height, width, lifetime, and heated fine structures near its base. © 2013. The American Astronomical Society. All rights reserved. Source


Kayshap P.,Aryabhatta Research Institute of Observational science ARIES | Srivastava A.K.,Aryabhatta Research Institute of Observational science ARIES | Murawski K.,Group of Astrophysics | Tripathi D.,University of Pune
Astrophysical Journal Letters | Year: 2013

We report an observation of a small-scale flux tube that undergoes kinking and triggers the macrospicule and a jet on 2010 November 11 in the north polar corona. The small-scale flux tube emerged well before the triggering of the macrospicule and as time progresses the two opposite halves of this omega-shaped flux tube bent transversely and approach each other. After ∼2 minutes, the two approaching halves of the kinked flux tube touch each other and an internal reconnection as well as an energy release takes place at the adjoining location and a macrospicule was launched which goes up to a height of 12 Mm. Plasma begins to move horizontally as well as vertically upward along with the onset of the macrospicule and thereafter converts into a large-scale jet in which the core denser plasma reaches up to ∼40 Mm in the solar atmosphere with a projected speed of ∼95 km s-1. The fainter and decelerating plasma chunks of this jet were also seen up to ∼60 Mm. We perform a two-dimensional numerical simulation by considering the VAL-C initial atmospheric conditions to understand the physical scenario of the observed macrospicule and associated jet. The simulation results show that reconnection-generated velocity pulse in the lower solar atmosphere steepens into slow shock and the cool plasma is driven behind it in the form of macrospicule. The horizontal surface waves also appeared with shock fronts at different heights, which most likely drove and spread the large-scale jet associated with the macrospicule. © 2013. The American Astronomical Society. All rights reserved. Source

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