Post on 05-Jan-2016
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Mode Parameter Variations from GONG Ring Diagrams: An Update
Rachel Howe, NSO
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Synopsis
• Lots of Data!
• Frequency shifts
• Power maps and amplitude shifts
• Summary
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Lots of Data
• We now have about 30 Carrington Rotations of GONG+ data analyzed, contiguous from 1980-2004 and then 2008-2012.
• 605 days, 114,345 dense-pack cubes.
• That’s 12Tb of data in the tracked velocity cubes.
• About 2.5Gb just in parameter tables.
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Frequency Shifts
• One rotation, after subtraction of geometric terms, for l=652, n=3
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Frequency shifts, 25 rotations
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Frequency variations from 25 rotations
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A thought
• Availability of frequencies for many rotations should allow detailed study of effect of active region evolution on local sound speed profile.
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Parameter sensitivity to B, by rotation
• Linear (left) and quadratic (right) coefficients for fits of frequency (top), and amplitude (bottom) against B.
• Colored ribbons correspond to different n.
• B from MDI daily synoptic images.
• Amplitude sensitivity seems to vary from rotation to rotation.
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Power Maps
• Take each tracked merged image (MI) data cube.
• Perform temporal FFT for each spatial pixel.
• Write 4-plane FITS file containing low-frequency (0.5 < < 1.5 mHz), 5-minute (1.5 < < 5.5 mHz) and high-frequency (5.5 < <7.5 mHz) total power, and mean velocity.
• Gzipped file is 0.25Mb for each dense cube.
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Power Maps
• Mosaic for one day (patches normalized separately: apparent gradient is artifact of overlap order).
• Take mean for each patch …
• and subtract fit to distance from disk center.
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Geometric Term in Amplitude
• Power vs distance from disk center, from rings (left) and power maps (right).
• Slope does not look constant.
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Slope of power against , from ring diagram fits.
• Possible correlation with apparent radius?
Time (days)
• Or with B?
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Summary
• GONG data are now plentiful!
• Power maps will be available.
• 5-minute power scaling not completely understood. – Ideas welcome.
• Stay tuned!