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The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m, the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 x 10[sup.-5]. For a 3-year data set, the fractional error is expected to be 3 x 10[sup.-6]. The GONG m-averaged frequency measurements differ from other helioseismic data sets ky 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure., Several million resonant acoustic normal modes (eigenmodes) of the sun are excited stochastically in the subsurface turbulent layer. The frequencies v, amplitudes A, and characteristic widths γ of such modes, [...]

Research suggests that giant convective cells are found at the sun's surface. Calculations show that long-lived velocity cells cover 29% of the sun's radius and may be involved in the geophysical process leading to sunspots. Their uneven distribution may be affected by differential solar rotation. Previous attempts to detect the giant cells have failed due to Doppler shift effects.

Dynamical and thermal variations of the internal structure of the Sun can affect the energy flow and result in variations in irradiance at the surface. Studying variations in the interior is crucial for understanding the mechanisms of the irradiance variations. “Global” helioseismology based on analysis of normal mode frequencies, has helped to reveal radial and latitudinal variations of the solar structure and dynamics associated with the solar cycle in the deep interior. A new technique, - “local-area” helioseismology or heliotomography, offers additional potentially important diagnostics by providing three-dimensional maps of the sound speed and flows in the upper convection zone. These diagnostics are based on inversion of travel times of acoustic waves which propagate between different points on the solar surface through the interior. The most significant variations in the thermodynamic structure found by this method are associated with sunspots and complexes of solar activity. The inversion results provide evidence for areas of higher sound speed beneath sunspot regions located at depths of 4–20 Mm, which may be due to accumulated heat or magnetic field concentrations. However, the physics of these structures is not yet understood. Heliotomography also provides information about large-scale stable longitudinal structures in the solar interior, which can be used in irradiance models. This new diagnostic tool for solar variability is currently under development. It will require both a substantial theoretical and modeling effort and high-resolution data to develop new capabilities for understanding mechanisms of solar variability. [Copyright &y& Elsevier]

Focuses on the use of the technique of travel-time helioseismology to detect the presence of strong downflows beneath the Sun's sunspots and the bright features known as plages. Theory on the formation of sunspots and downflows; Measurement of vertical magnetic field.

Shows that it is possible to extract time-distance information from temporal cross-correlations of the intensity fluctuations on the solar surface. This approach to the study of the solar interior opens the way for seismic studies of solar phenomena and should help to refine global models of the internal velocity stratification in the Sun. The high-frequency time-distance diagram; Helioseismology; More.

Presents observations from the South Pole on the composition and physics of the sun's interior and atmosphere using its acoustic oscillations. Measurement of blurring function directly from recorded solar images; Consideration of polar factors causing solar image blurring.