Study of the Solar Dynamics and its Evolution During Cycle 23 Based on an Improved Mode Fitting of a Solar Cycle Worth of Global Oscillation Network Group (GONG) Observations

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The Principal Investigator's objective is to infer the properties of internal solar rotation and its evolution during Solar Cycle 23, in order to provide key observational constraints on solar dynamo models. He plans to use an improved set of mode frequencies derived from nearly 13 years of Global Oscillation Network Group (GONG) observations. He will fit time series of various durations using a state-of-the-art methodology developed from past spacecraft observations, and then invert the resulting mode sets to obtain improved mode characteristics. The PI notes that this effort is timely, since the existing GONG data-fitting methodology was developed nearly 20 years ago and is not optimal. He expects his new fitting technique to be superior and to result in improved mode characteristics for GONG data. The proposer notes that the application of this technique to time series of GONG spherical harmonics coefficients will result in substantially improvements to assessments of solar internal structure, dynamics, and evolution.This work will increase the scientific return of the NSF-funded GONG project and will help address key scientific questions about solar variability. The PI's derived mode characteristics (frequency, line-width, asymmetry, and so forth) will be made freely available to the research community for additional scientific studies. The new fitting methodology will be provided to GONG project personnel, to allow them to integrate it into their standard data reduction process if deemed appropriate. The results from this effort also will complement existing analyses of older space-based data sets, will provide a unique cross-validation of these independent data sets fitted using the same methodology, and will allow the application of new state-of-the-art analysis techniques to Solar Cycle 24 data to be obtained by new solar instruments recently placed in orbit.