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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!