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Global Helioseismology Products

Global helioseismology is the study of the resonant modes of oscillation inside the Sun in order to infer the properties of the interior.

Algorithm for calculation:

The global helioseismology pipeline begins with a spherical harmonic decomposition. At present only dopplergrams are used as input, but other observables will be added in the future. Images are remapped to a uniform grid in longitude and sin(latitude), apodized, and an inner product is taken with a set of target spherical harmonic masks, yielding a complex amplitude as a function of spherical harmonic degree l and azimuthal order m for each image, up to l=1000. For each l and m a timeseries is constructed, typically of length 72 days, which are then detrended and gapfilled. Fourier transforms of these detrended and gapfilled timeseries are fitted to yield the mode parameters.


All of the above dataseries have T_START as their first primekey, which is slotted with a width of one day and an epoch of 1993.01.01_TAI-the MDI epoch (see AllAboutJsocNames). The exception is hmi.V_sht_gf_72d, which is a linked dataseries created for browsing. It has a slot width of 72 days so that one may search on any date and find the timeseries containing that date. When applicable, the next two primkeys will be LMIN and LMAX, although these will be equal for all timeseries and power spectra beyond hmi.V_sht_1d (they are retained for consistency among the dataseries). The last primekey will always be NDT, the number of points in the corresponding timeseries. The gaps data series have only T_START and NDT as primekeys, the rest have all four. These and other keyword definitions are given in the following table:

Available Products


The global pipeline consists of five modules and accompanying scripts:
  • jv2ts - takes dopplergrams as input and outputs timeseries chunked in l. It provides the combined functionality of three historic modules: v2helio, helio2mlat, and qdotprod.
  • jretile - input and output are timeseries, changes tiling in time and chunking in l.
  • jtsfiddle - detrends and gapfills timeseries. output can be timeseries, fourier transforms, power spectra, etc.
  • jtsslice - performs fourier transforms on a section of a timeseries to save on I/O.
  • jpkbgn - extracts mode parameters from fourier transforms. currently input are timeseries, output are ascii tables.

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