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Abhishek K. Srivastava

Publications and source records attributed to Abhishek K. Srivastava.

22 records · Page 2Linked to original sources

Observations of Post-flare Plasma Dynamics during an M1.0 Flare in AR11093 by SDO/AIA

We observe the motion of cool and hot plasma in a multi-stranded post flare loop system that evolved in the decay phase of a two ribbon M1.0 class flare in AR 11093 on 7 August 2010 using SDO/AIA 304 Å and 171 Å filters. The moving intensity feature and its reflected counterpart are observed in the loop system at multi-temperature. The observed hot counterpart of the plasma that probably envelopes the cool confined plasma, moves comparatively faster ($\sim$34 km s$^{-1}$) to the later (29 km s$^{-1}$) in form of the spreaded 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 post flare loop system through impulsive flare heating processes. Complementing our observations of moving multi-temperature intensity features in the post flare loop 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.

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On the Triggering of M-Class Solar Flare due to Loop-loop Interaction in AR NOAA 10875

We present multiwavelength analysis of an M7.9 /1N solar flare which occurred on 27 April 2006 in AR NOAA 10875. The flare was triggered due to the interaction of two loop systems. GOES soft X-ray and TRACE 195 Å image sequences show the observational evidences of 3-D X-type loop-loop interaction with converging motion at the interaction site. We found the following characteristics during the loop- loop interaction: (i) a short duration/impulsive flare obeying the Neupart effect, (ii) double peak structure in radio flux profiles (in 4.9 and 8.8 GHz), (iii) quasi-periodic oscillations in the radio flux profiles for the duration of \sim3 min, (iv) absence of CME and type III radio burst. The above characteristics observed during the flare are in agreement with the theory and simulation of current loop coalescence by Sakai et al. (1986). These are unique multiwavelength observations, which provide the evidences of loop-loop interaction and associated triggering of solar flare without CME.

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Numerical simulations of solar macrospicules

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 the recent numerical model of spicule formation (Murawski & Zaqarashvili 2010) 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 A) 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.

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Observations of a pulse driven cool polar jet by SDO/AIA

Context. We observe a solar jet at north polar coronal hole (NPCH) using SDO AIA 304 °A 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 observed solar jet by implementing a realistic (VAL-C) model of solar temperature. Methods. We solve two-dimensional ideal magnetohydrodynamic equations numerically to simulate the observed solar jet. We consider a localized velocity pulse that is essentially parallel to the background magnetic field lines and 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 produces in general the observed properties of the jet, e.g., upward and backward average velocities, height, width, life-time, and ballistic nature. Conclusions. The close matching between the jet observations and numerical simulations provides first strong evidence for the formation of this jet by a single velocity pulse. The strong velocity pulse is most likely generated by the low- atmospheric reconnection in the polar region which results in triggering of the jet. The downflowing material of the jet most likely vanishes in the next upcoming velocity pulses from lower solar atmosphere, and therefore distinctly launched a single jet upward in the solar atmosphere is observed.

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