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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]

Reports research which detected long-lived velocity cells at the surface of the Sun. Projected span of giant convective cells; Large aspect ratio of cells; Impact of rotational shear.

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.