On the Origin of High-Frequency "Acoustic'' Power in Photospheric and Chromospheric Velocity Power Spectra

Details On the Origin of High-Frequency "Acoustic'' Power in Photospheric and Chromospheric Velocity Power Spectra On the Origin of High-Frequency "Acoustic'' Power in Photospheric and Chromospheric Velocity Power Spectra

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21640309f&link_type=abstract

American Astronomical Society, AAS Meeting #216, #403.09; Bulletin of the American Astronomical Society, Vol. 41, p.879

Astronomy and Astrophysics

Astronomy

Scientific paper

In a recent paper (Fleck et al., 2010) we compared observed Dopplergram time series from Hinode with results from 3-D numerical simulations based on the Oslo "Stagger” and CO5BOLD codes. Given the rapid falloff of atmospheric modulation transfer functions at high frequencies due to the extended widths of typical velocity response functions, one would expect the high-frequency tail of Doppler power spectra to drop significantly below those of actual velocities at the corresponding heights in the simulations. Surprisingly, our analysis of power spectra of Doppler shifts of simulated line profiles did not reveal such a steep falloff at high frequencies. Instead, they are comparable to (and in some cases even larger than) those of the actual velocities, making estimates of the energy flux of high frequency acoustic waves questionable, in particular those that apply atmospheric MTF corrections. In this work we study the cause of this unexpected behavior in detail, with particular emphasis on the role of rapidly changing velocity response functions in a dynamic atmosphere with strong vertical velocity gradients.

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