Session 53 - First Results from the Global Oscillations Network Group (GONG).
Oral session, Wednesday, June 12
Wisconsin Center,

## [53.06] The Sun's Acoustic Spectrum and Normal Mode Parameters

R. T. Stebbins (JILA/U. Colorado), F. Hill (NSO/NOAO), P. B. Stark (UC Berkeley), G. D. Reduction, Analysis Team

GONG seeks to measure the frequencies, amplitudes and line widths of the Sun's acoustic normal modes. The Project estimates these parameters for more than 250,000 acoustic modes of the Sun from every 36 day-long set of data. Data from the network are archived, calibrated, reduced to several science products and made available for distribution to researchers at the pace of observations. GONG also produces magnetograms and temporally filtered solar images for convective velocity and magnetic field studies.

The frequency resolution of a single data set is 0.321 \muHz. For m- averaged frequencies the median formal error is 0.044 \muHz, and the associated median fractional frequency error is 1.6 \times 10^-5. Results from concatenated data sets are now becoming available. For a three-year data set, the fractional error is expected to be 3 \times 10^-6, providing the highest quality helioseismic frequency measurements to date. Examples of power spectra and mode parameters will be shown.

To demonstrate the reliability of the initial GONG frequencies, m-averaged frequency measurements will be compared with other helioseismic data sets. The mean systematic variations among the data sets are 0.03 to 0.08 \muHz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure and dynamics. Error sources will be discussed.