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D.C. Braun (NorthWest Res. Assoc., CoRA Division), C. Lindsey (Solar Phys. Res. Corp.)
Since mid-2001, the upgraded GONG+ network has been providing high-resolution Doppler images of the Sun. We are now analyzing GONG+ data as part of our program in local helioseismology and acoustic holography. The bulk of the results shown here are derived from data obtained during a 24-hour period in 2001 September, when simultaneous full-disk observations from the MDI instrument onboard the SOHO spacecraft were available for comparison. Images showing the acoustic travel-time perturbations over the entire far hemisphere obtained from GONG+ and MDI data are essentially identical. This demonstrates that the GONG+ network may be used as the basis of a synoptic far-side imaging program of comparable quality to that now provided by MDI. Holographic depth-diagnostics of travel-time perturbations below several active regions on the solar front side are also presented. These phase-sensitive holographic images from GONG+ and MDI have similar noise characteristics when computed using acoustic modes with degree (wavenumber) below about 300, which implies that the r.m.s. fluctuations in these images are solar in nature. At higher wavenumbers, atmospheric seeing introduces an excess r.m.s., which increases with mode degree, to the images derived from GONG+ data. However, acceptable images are possible using modes with degrees up to at least 700. We will discuss how GONG+ data may be advantageously utilized in detailed, continuous, and long-term local-helioseismic analyses of the far side and deep interior of the Sun.
This work is supported by awards AST-9987286 from NSF, and awards NASW-01007 and NAG5-10984 from NASA.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.