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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.


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

We perform numerical simulations of impulsively generated Alfvén waves in an isolated solar arcade, which is gravitationally stratified and magnetically confined. We study numerically the propagation of Alfvén waves along the magnetic structure that extends from the lower chromosphere, where the waves are generated, to the solar corona, and analyze the influence of the arcade size and the width of the initial pulses on the wave propagation and reflection. Our model of the solar atmosphere is constructed by adopting the temperature distribution based on the semi-empirical VAL-C model and specifying the curved magnetic field lines that constitute the asymmetric magnetic arcade. The propagation and reflection of Alfvén waves in this arcade is described by 2.5-dimensional magnetohydrodynamic equations that are numerically solved by the FLASH code. Our numerical simulations reveal that the Alfvén wave amplitude decreases as a result of a partial reflection of Alfvén waves in the solar transition region, and that the waves that are not reflected leak through the transition region and reach the solar corona. We also find the decrement of the attenuation time of Alfvén waves for wider initial pulses. Moreover, our results show that the propagation of Alfvén waves in the arcade is affected by the spatial dependence of the Alfvén speed, which leads to phase mixing that is stronger for more curved and larger magnetic arcades. We discuss the processes that affect the Alfvén wave propagation in an asymmetric solar arcade and conclude that besides phase mixing in the magnetic field configuration, the plasma properties of the arcade, the size of the initial pulse, and the structure of the solar transition region all play a vital role in the Alfvén wave propagation. © 2014. The American Astronomical Society. All rights reserved.


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..


Chmielewski P.,Group of Astrophysics | Srivastava A.K.,Aryabhatta Research Institute of Observational science ARIES | Murawski K.,Group of Astrophysics | Musielak Z.E.,University of Texas at Arlington | Musielak Z.E.,Kiepenheuer Institute for Solar Physics
Monthly Notices of the Royal Astronomical Society | Year: 2013

We study the impulsively generated non-linear Alfvén waves in the solar atmosphere and describe their most likely role in the observed non-thermal broadening of some spectral lines in solar coronal holes. We solve numerically thetime-dependent magnetohydrodynamic equations to find temporal signatures of large-amplitude Alfvén waves in the solar atmosphere model of open and expanding magnetic field configuration, with a realistic temperature distribution. We calculate the temporally and spatially averaged, instantaneous transversal velocity of non-linear Alfvén waves atdifferent heights of the model atmosphere and estimate its contribution to the unresolved non-thermal motions caused by the waves. We find that the pulse-driven non-linear Alfvén waves with the amplitude Av = 50 km s-1 are the most likely candidates for the non-thermal broadening of Si VIII Λ1445.75Å line profiles inthe polar coronal hole as reported by Banerjee et al. We also demonstrate that the Alfvén waves driven by comparatively smaller velocity pulse with amplitude Av = 25 km s-1 may contribute to the spectral line width of the same line at various heights in coronal hole broadening. We conclude that the non-linear Alfvén waves excited impulsively in the lower solar atmosphere may be reant result as it allows us to conclude that such large amplitude and pulse-driven Asponsible for the observed spectral line broadening in polar coronal holes. This is an importlfvén waves may indeed exist in solar coronal holes. The existence of these waves may impart the required momentum to accelerate the solar wind. © 2012 The Authors.


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.


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.


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.


Murawski K.,Group of Astrophysics | Srivastava A.K.,Aryabhatta Research Institute of Observational science ARIES | Zaqarashvili T.V.,Austrian Academy of Sciences | Zaqarashvili T.V.,Ilia State University
Astronomy and Astrophysics | Year: 2011

Context. We consider a localized pulse in the component of velocity, parallel to the ambient magnetic field lines, that is initially launched in the solar chromosphere. Aims. We aim to generalize our recent numerical model of spicule formation by implementing a VAL-C model of solar temperature. Methods. With the use of the code FLASH we solve two-dimensional ideal magnetohydrodynamic equations numerically to simulate the solar macrospicules. Results. Our numerical results reveal that the pulse located below the transition region triggers plasma perturbations, which exhibit many features of macrospicules. We also present an observational (SDO/AIA 304 Å) case study of the macrospicule that approximately mimics the numerical simulations. Conclusions. In the frame of the model we devised, the solar macrospicules can be triggered by velocity pulses launched from the chromosphere. © 2011 ESO.


Srivastava A.K.,Group of Astrophysics | Srivastava A.K.,Aryabhatta Research Institute of Observational science ARIES | Murawski K.,Group of Astrophysics
Astronomy and Astrophysics | Year: 2011

Context. We observe a solar jet at north polar coronal hole (NPCH) using SDO AIA 304 Å image data on 3 August 2010. The jet rises obliquely above the solar limb and then retraces its propagation path to fall back. Aims. We numerically model this solar jet by implementing a realistic (VAL-C) model of solar temperature. Methods. We solve two-dimensional ideal magnetohydrodynamic equations numerically to simulate the solar jet. We consider a localized velocity pulse that is essentially parallel to the background magnetic field lines and is initially launched at the top of the solar photosphere. The pulse steepens into a shock at higher altitudes, which triggers plasma perturbations that exhibit the observed features of the jet. The typical direction of the pulse also clearly exhibits the leading front of the moving jet. Results. Our numerical simulations reveal that a large amplitude initial velocity pulse launched at the top of the solar photosphere in general produces the observed properties of the jet, e.g., upward and backward average velocities, height, width, life-time, and ballistic nature. Conclusions. The close match between the jet observations and numerical simulations provides a first strong evidence that this jet is formed by a single velocity pulse. The strong velocity pulse is most likely generated by the low-atmospheric reconnection in the polar region, which triggers the jet. The downflowing material of the jet most likely is absorbed in the next upcoming velocity pulses from the lower solar atmosphere, and because of that we only see a single jet moving upward in the solar atmosphere. © 2011 ESO.


Murawski K.,Group of Astrophysics | Solov'ev A.,Russian Academy of Sciences | Kraskiewicz J.,Group of Astrophysics
Solar Physics | Year: 2015

We generalize our analytical and numerical models of the solar flux tube on twisted magnetic-field lines. The basic equations and numerical methods have much in common with those of Murawski et al. (Astron. Astrophys.577, A126, 2015); the new and important issue is the twisted magnetic-field component that couples explored torsional Alfvén and magnetoacoustic waves. In these models we specify a magnetic-flux function and derive general analytical formulas for the equilibrium mass density and a gas pressure. We use the developed models, which can be adopted for any axisymmetric structure with twisted and untwisted magnetic lines, to simulate the MHD waves. These waves are excited by a localized pulse in the azimuthal velocity component that is launched at the top of the solar photosphere. Their propagation through the solar chromosphere and transition region to the solar corona reveals a complex scenario of twisted magnetic-field lines and flows associated with torsional Alfvén and magnetoacoustic waves. © 2015, Springer Science+Business Media Dordrecht.

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