台灣清華大學, 物理系 Helioseismology (II) Global and Local Helioseismology (2010.08,...
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Transcript of 台灣清華大學, 物理系 Helioseismology (II) Global and Local Helioseismology (2010.08,...
![Page 1: 台灣清華大學, 物理系 Helioseismology (II) Global and Local Helioseismology (2010.08, 北京 ) 周定一 Dean-Yi Chou.](https://reader033.fdocument.pub/reader033/viewer/2022061605/5697bf7d1a28abf838c8482f/html5/thumbnails/1.jpg)
台灣清華大學, 物理系
Helioseismology (II)
Global and Local Helioseismology
(2010.08, 北京 )
周定一 Dean-Yi Chou
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Helioseismolgy
Using solar p-mode oscillations (waves) measured on the solar surface to probe the solar interior.
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Basic Principle to probe Solar Interiors
Different modes penetrate into different depths.
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Observations in Helioseismology
Using solar p-mode oscillations (waves) measured on the solar surface to probe the solar interior.
Observations set r = R
But it still gives the same dispersion relation:
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Local Helioseismolgy
Using solar p modes measured on the solar surface to probe the local properties of the solar interior.
Global Helioseismolgy
Using solar p modes measured on the solar surface to probe the global properties of the solar interior.
The life time of p modes used in global helioseismology needs to be long enough to go around the Sun.
This gives a criterion: l < 150
It needs higher l (shorter wavelength).
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Examples of Important Achievements in Global Helioseismology
• Confirm and refine the standard model
• Depth dependence of sound speed
• Differential rotation pattern
• Wave excitation mechanism
• Solar-cycle variations of rotation and sound speed near the base of the convection zone ???
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Observations in Helioseismology
Using solar p-mode oscillations (waves) measured on the solar surface to probe the solar interior.
Observations set r = R
But it still gives the same dispersion relation:
![Page 8: 台灣清華大學, 物理系 Helioseismology (II) Global and Local Helioseismology (2010.08, 北京 ) 周定一 Dean-Yi Chou.](https://reader033.fdocument.pub/reader033/viewer/2022061605/5697bf7d1a28abf838c8482f/html5/thumbnails/8.jpg)
k-ω Diagram
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Sound Speed and Density Profile
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Internal Differential Rotation
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Internal Differential Rotation
(comparison of different methods)
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Local Helioseismolgy
Using solar p-mode oscillations measured on the solar surface to probe the local properties of the solar interior.
Local properties (local inhomegeneity):
1. magnetic fields
2. flows
3. thermal perturbation
4. other local properties
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> Fourier-Hankel decomposition (Braun et al. 1987)> Ring-diagram Analysis (Hill 1988)> Time-Distance Analysis (Duvall et al. 1993)> Acoustic Imaging (Chang et al. 1997)> Holography ? (Chou et al. 2007)> Direction Filter (Chou et al. 2009)
Techniques in Local Helioseismology
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Examples of Important Achievements in Local Helioseismology
• Flows around sunspots
• Flows in the convection zone (near surface)
• Sound-speed perturbation around sunspots
• Meridional flows in the convection zone (distribution and solar-cycle variations)
• Acoustic power in sunspots
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Ring-diagram Analysis (Hill 1988)
Basic principle:
1. Flows affect p-mode frequencies.
2. 2-d flow patterns can be derived from frequency shifts.
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The average velocity over the region, (Ux, Uy), is determined by fitting power spectra to
It needs inversion to obtain depth distribution.
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Flow pattern from ring-diagram analysis
d = 7.1 Mm
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Time-Distance Analysis (Duvall et al. 1993)
Measuring changes in travel time due to inhomogeneity
Cross-correlation functions1
2
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Fit cross-correlation functions to a Gabor wavelet
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Information from travel time
flow velocity
wave speed perturbation
Through inversion, the distributions of flow velocity and wave speed perturbation below the surface can be obtained.
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Time-Distance Analysis (Duvall et al. 1993)
Measuring changes in travel time due to inhomogeneity
Cross-correlation functions1
2
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Kosovichev et al. (2000) (MDI data)
flow velocity and wave-speed perturbation in an active region
from time-distance analysis
16 Mm
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wave-speed perturbation for an active region
Kosovichev et al. (2000) (MDI data)
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Kosovichev et al. (2000) (MDI data)
wave-speed perturbation for an emerging flux region
8 hour interval
1
2
3
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Acoustic Imaging (Chang et al., 1997)
Is it possible to image the solar interior with acoustic waves measured on the surface?
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imaging = adding signals in phase
Principle of imaging
There is no such a lens for the solar interior.
One needs a computational lens.
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Constructed Images from Acoustic Imaging
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Although the computation lens is focused on the target point, information along the ray path is contained in the signals used in reconstruction.
The phase and intensity information at a target point include information along the ray path.
One needs to do inversion to obtain more precise distribution of inhomogeneity.
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Sound-speed perturbation from inversion of travel-time perturbation in acoustic imaging
vertical cut
measured inversion
measured inversion
(Sun & Chou, 2001)
54Mm
169 Mm
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Acoustic imaging technique has been used to map the far side of the Sun.
Application:
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Limits of local helioseimology
> Modes of longer wavelength penetrate deeper.
> β increases with depth rapidly.
1. Limit on spatial resolution
2. Limit on depth
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The EndThe End