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arXiv · 1506.06993

Spectroscopic Observations and Modelling of Impulsive Alfvén Waves Along a Polar Coronal Jet

P. Jelínek·A. K. Srivastava·K. Murawski·P. Kayshap·B. N. Dwivedi
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Abstract

Using the Hinode/EIS 2$"$ spectroscopic observations, we study the intensity, velocity, and FWHM variations of the strongest Fe XII 195.12 Å line along the jet to find the signature of Alfvén waves. We simulate numerically the impulsively generated Alfvén waves within the vertical Harris current-sheet, forming the jet plasma flows, and mimicking their observational signatures. Using the FLASH code and the atmospheric model with embedded weakly expanding magnetic field configuration within a vertical Harris current-sheet, we solve the two and half-dimensional (2.5-D) ideal magnetohydrodynamic (MHD) equations to study the evolution of Alfvén waves and vertical flows forming the plasma jet. At a height of $\sim 5~\mathrm{Mm}$ from the base of the jet, the red-shifted velocity component of Fe XII 195.12 Å line attains its maximum ($5~\mathrm{km\,s}^{-1}$) which converts into a blue-shifted one between the altitude of $5-10~\mathrm{Mm}$. The spectral intensity continously increases up to $10~\mathrm{Mm}$, while FWHM still exhibits the low values with almost constant trend. This indicates that the reconnection point within the jet's magnetic field topology lies in the corona $5-10~\mathrm{Mm}$ from its footpoint anchored in the Sun's surface. Beyond this height, FWHM shows a growing trend. This may be the signature of Alfvén waves that impulsively evolve due to reconnection and propagate along the jet. From our numerical data, we evaluate space- and time- averaged Alfvén waves velocity amplitudes at different heights in the jet's current-sheet, which contribute to the non-thermal motions and spectral line broadening. The synthetic width of Fe XII $195.12~\mathrmÅ$ line exhibits similar trend of increment as in the observational data, possibly proving the existence of impulsively generated (by reconnection) Alfvén waves which propagate along the jet.

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P. Jelínek, A. K. Srivastava, K. Murawski, P. Kayshap, B. N. Dwivedi. 2015-06-23. Spectroscopic Observations and Modelling of Impulsive Alfvén Waves Along a Polar Coronal Jet. https://doi.org/10.1051/0004-6361%2F201424234

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