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Pulse-driven nonlinear Alfvén waves and and their role in e the spectral line broadening  

Piotr Chmielewski   Submitted: 2012-07-25 13:21

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 the time-dependent magnetohydrodynamic equations to find temporal signatures of large-amplitude Alfvén waves in the model atmosphere 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 at different heights of the model atmosphere, and estimate its contribution in the unresolved non-thermal motions caused by the waves. We find that the non-linear, pulse-driven Alfvén waves with the amplitude Av =50 km s-1 are the most likely candidates for the non-thermal broadening of Si VIII λ1445.75? line profiles in the polar coronal hole as reported by Banerjee et al. (1998). We also demonstrate that the Alfvén waves driven by comparatively smaller velocity pulse with its amplitude Av =25 km s-1 may contribute to the spectral line width of Si VIII λ1445.75? at various heights in coronal hole as reported by Dolla & Soloman (2008), however, without any significant role in its observed broadening. Some agreement of our results with observational data gives an indirect evidence for the existence of larger amplitude, pulse-driven Alfvén waves in solar coronal holes. The main conclusion of this paper is that non-linear Alfvén waves excited impulsively in the lower solar atmosphere of polar coronal holes are responsible for some observed spectral line broadening. This is an important result as it allows us to conclude that such large amplitude and pulse-driven Alfvén waves do indeed exist in solar coronal holes. The existence of these waves and their undamped growth may impart the required momentum to accelerate the solar wind.

Authors: P. Chmielewski, A.K. Srivastava, K. Murawski, and Z.E. Musielak
Projects: None

Publication Status: Submitted
Last Modified: 2012-07-25 14:18
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Pulse-driven nonlinear Alfv?n waves and and their role in e the spectral line broadening

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