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We use five-day helioseimic data from the Taiwan Oscillation Network to study the flow around a sunspot, NOAA 7887. The p-mode oscillations in an annular region centered at the sunspot are decomposed into the modes propagating toward and away from the sunspot. We find that the frequency of an outgoing mode is greater than that of the corresponding incoming mode. This indicates that the plasma is flowing outward from the sunspot. The outflow velocity is estimated to be about 40–80 m s-1. 相似文献
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Hui Zhao Dean-Yi Chou Ming-Hsu Yang Zhi-Chao Liang Ming-Tsung Sun 《Solar physics》2011,268(2):363-376
The cross-correlation function is a useful tool in helioseismology. The magnitude of the cross-correlation function has been used to represent the power of wave packets. Dispersion causes a decrease in amplitude and an increase in width of wave packets. This leads to a decrease in magnitude and an increase in width of cross-correlation functions. The effect of dispersion on the magnitude of cross-correlation functions needs to be adequately corrected for in order to use the magnitude of cross-correlation functions to represent the power of wave packets. In this study, we investigate how the magnitude of cross-correlation functions changes with the number of skips owing to dispersion and the method to correct it. Our study, using simulated and observational data, indicates that the correction should be three dimensional instead of the one-dimensional correction adopted in previous studies. Using the three-dimensional correction, the measured dissipation rate in the quiet Sun is smaller than the value of previous studies. 相似文献
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We study the properties of power maps of solar acoustic waves filtered with direction filters and phase-velocity filters.
A direction filter is used to isolate acoustic waves propagating in a narrow range of directions. The acoustic-power map of
the waves filtered with a direction filter shows extended reduced-power features behind magnetic regions with respect to the
wave direction. A phase-velocity filter is further applied to isolate waves with similar wave paths. In the power maps of
the waves filtered with both a direction filter and a phase-velocity filter, a reduced-power image of a sunspot appears behind
the sunspot with respect to the wave direction. The distance between the sunspot and the secondary image is consistent with
the one-skip travel distance of the wave packet associated with the phase-velocity filter. The waves filtered with direction
and phase-velocity filters at the location of the secondary image could be used to probe the sunspot. In the quiet Sun, spatial
fluctuations exist in any acoustic-power map. These fluctuations are mainly caused by interference among modes with the same
frequency. The fluctuations are random with two properties: They change rapidly with time, and their magnitude decreases with
the square root of the number of frames used in computing the acoustic-power map. 相似文献
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Dean-Yi Chou Ming-Tsung Sun Teng-Yi Huang Shih-Ping Lai Pi-Jen Chi Knight-Tien Ou Chang-Chi Wang Jui-Yang Lu An-Li Chu Chi-Seng Niu et al. 《Solar physics》1995,160(2):237-243
The Taiwan Oscillation Network (TON) is a ground-based network to measure solar intensity oscillations to study the internal structure of the Sun. K-line full-disk images of 1000 pixels diameter are taken at a rate of one image per minute. Such data would provide information onp-modes withl as high as 1000. The TON will consist of six identical telescope systems at proper longitudes around the world. Three telescope systems have been installed at Teide Observatory (Tenerife), Huairou Solar Observing Station (near Beijing), and Big Bear Solar Observatory (California). The telescopes at these three sites have been taking data simultaneously since October of 1994. Anl – v diagram derived from 512 images is included to show the quality of the data. 相似文献
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The three-dimensional distribution of change in phase travel time of an active region below the solar surface can be constructed
with the technique of acoustic imaging. The interpretation of the distribution of measured phase travel time perturbation
suffers from the finite spatial resolution of the acoustic lenses. In the ray approximation, the phase travel time perturbation
measured in acoustic imaging can be expressed as an integral of the product of the relative sound-speed perturbation and a
kernel. Forward computations show that the vertical resolution of phase travel time perturbation is poor even in the ray approximation.
In this study, we discuss the inversion of phase travel time perturbations to estimate the relative sound-speed perturbation
with a regularized least-squares inversion method. The tests with model perturbations of sound speed show that the inversion
reasonably recovers the distribution of the model perturbation. We also apply the inversion method to the measured phase travel
time perturbation of active region NOAA 7981. 相似文献
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