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Evidence of Shock-Driven Turbulence in the Solar Chromosphere  

Kevin Reardon   Submitted: 2008-10-28 15:02

We study the acoustic properties of the solar chromosphere in the high-frequency regime using a time sequence of velocity measurements in the chromospheric Ca II 854.2 nm line taken with the Interferometric Bidimensional Spectrometer (IBIS). We concentrate on quiet-Sun behavior, apply Fourier analysis, and characterize the observations in terms of the probability density functions (PDFs) of velocity increments. We confirm the presence of significant oscillatory fluctuation power above the cutoff frequency and find that it obeys a power-law distribution with frequency up to our 25~mHz Nyquist limit. The chromospheric PDFs are non-Gaussian and asymmetric and they differ among network, fibril, and internetwork regions. This suggests that the chromospheric high-frequency power is not simply the result of short-period waves propagating upward from the photosphere but rather is the signature of turbulence generated within the chromosphere from shock oscillations near the cutoff frequency. The presence of this pervasive and broad spectrum of motions in the chromosphere is likely to have implications for the excitation of coronal loop oscillations.

Authors: K.P. Reardon, F. Lepreti, V. Carbone, A. Vecchio
Projects: National Solar Observatory (Sac Peak)

Publication Status: Published in Astrophys. J. Lett., v683, L207
Last Modified: 2008-11-01 10:03
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Photon Spectroscopy with Imaging X-Ray Instruments  

Kevin Reardon   Submitted: 2007-03-09 03:06

Individual X-ray photons in the keV energy range produce hundreds of photoelectrons in a single pixel of a CCD array detector. The number of photoelectrons produced is a linear function of the photon energy, allowing the measurement of spectral information with an imaging detector system. Most solar X-ray telescopes, such as Yohkoh/SXT and Hinode/XRT, use CCD detectors in an integrating mode and are designed to make temperature estimates from multiband filter photometry. We show how such instruments can be used in a new way to perform a limited type of this photon spectroscopy. By measuring the variance in intensity of a series of repeated images through a single filter of an X-ray source, the mean energy per detected photon can be determined. This energy is related to the underlying coronal spectrum, and hence it can be used to deduce the mean plasma temperature. We apply this technique to data from the Yohkoh Soft X-Ray Telescope and compare the temperatures obtained with this technique with the temperatures derived using the standard filter ratio method for a postflare loop system. Given the large dynamic range of the soft X-ray flux observed from the Sun, we describe the requirements for a future instrument that would be better suited to performing photon spectroscopy.

Authors: Labonte, B.J., Reardon,K.P.
Projects: Hinode,Yohkoh-SXT

Publication Status: Solar Physics, in press
Last Modified: 2007-03-09 09:50
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Evidence of Shock-Driven Turbulence in the Solar Chromosphere
Photon Spectroscopy with Imaging X-Ray Instruments

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