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Title: MEASUREMENTS OF THE WAVEFUNCTIONS OF SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS

Abstract

Solar acoustic waves are scattered by sunspots because of the interaction between the acoustic waves and sunspots. We use a deconvolution scheme to obtain the wavefunction of the acoustic wave on the solar surface at various times from cross-correlation functions computed between an incident wave and the signals at other points on the surface. The wavefunction of the scattered wave is obtained by subtracting the wavefunction of the incident wave from that of the total wave. We study the wavefunctions of scattered waves with the incident waves of radial order n = 0-5 for two sunspots, NOAAs 11084 and 11092. The scattered wave is predominant in the forward direction of the incident wave, but its wavefronts are curved. The shape of the wavefronts depends on the ratio of sunspot dimension to wavelength of the incident wave. The smaller the ratio is, the closer to circular the scattered wave is. The scattering strength, i.e. the magnitude of the scattered wave relative to that of the incident wave, decreases with the radial order n. This suggests that the region generating the scattered wave is shallower than the depth of the f-modes.

Authors:
; ;  [1]
  1. Physics Department, National Tsing Hua University, Hsinchu, Taiwan (China)
Publication Date:
OSTI Identifier:
21587393
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 740; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/740/2/56; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CORRELATION FUNCTIONS; INTERACTIONS; SCATTERING; SOUND WAVES; SUN; SUNSPOTS; WAVE FUNCTIONS; FUNCTIONS; MAIN SEQUENCE STARS; SOLAR ACTIVITY; STARS; STARSPOTS; STELLAR ACTIVITY

Citation Formats

Zhao Hui, Chou, Dean-Yi, and Yang, Ming-Hsu, E-mail: chou@phys.nthu.edu.tw. MEASUREMENTS OF THE WAVEFUNCTIONS OF SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS. United States: N. p., 2011. Web. doi:10.1088/0004-637X/740/2/56; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Zhao Hui, Chou, Dean-Yi, & Yang, Ming-Hsu, E-mail: chou@phys.nthu.edu.tw. MEASUREMENTS OF THE WAVEFUNCTIONS OF SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS. United States. doi:10.1088/0004-637X/740/2/56; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Zhao Hui, Chou, Dean-Yi, and Yang, Ming-Hsu, E-mail: chou@phys.nthu.edu.tw. 2011. "MEASUREMENTS OF THE WAVEFUNCTIONS OF SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS". United States. doi:10.1088/0004-637X/740/2/56; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21587393,
title = {MEASUREMENTS OF THE WAVEFUNCTIONS OF SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS},
author = {Zhao Hui and Chou, Dean-Yi and Yang, Ming-Hsu, E-mail: chou@phys.nthu.edu.tw},
abstractNote = {Solar acoustic waves are scattered by sunspots because of the interaction between the acoustic waves and sunspots. We use a deconvolution scheme to obtain the wavefunction of the acoustic wave on the solar surface at various times from cross-correlation functions computed between an incident wave and the signals at other points on the surface. The wavefunction of the scattered wave is obtained by subtracting the wavefunction of the incident wave from that of the total wave. We study the wavefunctions of scattered waves with the incident waves of radial order n = 0-5 for two sunspots, NOAAs 11084 and 11092. The scattered wave is predominant in the forward direction of the incident wave, but its wavefronts are curved. The shape of the wavefronts depends on the ratio of sunspot dimension to wavelength of the incident wave. The smaller the ratio is, the closer to circular the scattered wave is. The scattering strength, i.e. the magnitude of the scattered wave relative to that of the incident wave, decreases with the radial order n. This suggests that the region generating the scattered wave is shallower than the depth of the f-modes.},
doi = {10.1088/0004-637X/740/2/56; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal},
number = 2,
volume = 740,
place = {United States},
year = 2011,
month =
}
  • The solar acoustic waves around a sunspot are modified because of the interaction with the sunspot. The interaction can be viewed as that the sunspot, excited by the incident wave, generates the scattered wave, and the scattered wave is added to the incident wave to form the total wave around the sunspot. We define an interaction parameter, which could be complex, describing the interaction between the acoustic waves and the sunspot. The scattered wavefunction on the surface can be expressed as a two-dimensional integral of the product of the Green's function, the wavefunction, and the two-dimensional interaction parameter over themore » sunspot area for the Born approximation of different orders. We assume a simple model for the two-dimensional interaction parameter distribution: its absolute value is axisymmetric with a Gaussian distribution and its phase is a constant. The measured scattered wavefunctions of various modes for NOAAs 11084 and 11092 are fitted to the theoretical scattered wavefunctions to determine the three model parameters, magnitude, Gaussian radius, and phase, for the Born approximation of different orders. The three model parameters converge to some values at high-order Born approximations. The result of the first-order Born approximation is significantly different from the convergent value in some cases. The rate of convergence depends on the sunspot size and wavelength. It converges more rapidly for the smaller sunspot and longer wavelength. The magnitude increases with mode frequency and degree for each radial order. The Gaussian radius is insensitive to frequency and degree. The spatial range of the interaction parameter is greater than that of the continuum intensity deficit, but smaller than that of the acoustic power deficit of the sunspot. The phase versus phase speed falls into a small range. This suggests that the phase could be a function phase speed. NOAAs 11084 and 11092 have a similar magnitude and phase, although the ratio of their sizes is 0.75.« less
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  • Solar acoustic waves are scattered by a sunspot due to the interaction between the acoustic waves and the sunspot. The sunspot, excited by the incident wave, generates the scattered wave. The scattered wave is added to the incident wave to form the total wave around the sunspot. The interference fringes between the scattered wave and the incident wave are visible in the intensity of the total wave because the coherent time of the incident wave is of the order of a wave period. The strength of the interference fringes anti-correlates with the width of temporal spectra of the incident wave.more » The separation between neighboring fringes increases with the incident wavelength and the sunspot size. The strength of the fringes increases with the radial order n of the incident wave from n = 0 to n = 2, and then decreases from n = 2 to n = 5. The interference fringes play a role analogous to holograms in optics. This study suggests the feasibility of using the interference fringes to reconstruct the scattered wavefields of the sunspot, although the quality of the reconstructed wavefields is sensitive to the noise and errors in the interference fringes.« less
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