Back to Volume
Paper: The Observational Helioseismology Programs at the Sacramento Peak and Mount Wilson Observatories
Volume: 478, Fifty Years of Seismology of the Sun and Stars
Page: 61
Authors: Rhodes Jr., E. J.
Abstract: The starting point for the study of the solar interior using helioseismology can be identified with the observational confirmation by Deubner (1975) and independently by Rhodes (1977); Rhodes et al. (1976a,b, 1977a) of the standing wave nature of the solar “5-minute” oscillations as proposed by Ulrich (1970) and independently by Leibacher & Stein (1971). The pioneering observations of the Rhodes et al. (1977a) study were obtained using what is now the Dunn Solar Telescope (DST) at the Sacramento Peak National Observatory in early 1975. Subsequent helioseismic observations were also obtained at the DST, but one of the major drawbacks of all of these early studies was the fact that the DST could only be dedicated to these studies for a few days at a time. Consequently, the 60-Foot Solar Tower of the Mount Wilson Observatory (MWO) was converted into a dedicated helioseismology telescope. The initial observations there were obtained in 1984. These observations were employed later in several studies of solar internal rotation. An important outcome of these early observations was the discovery of the Solar Subsurface Shear Layer (SSL). The 60-Foot Tower was upgraded with the installation of a one-mega-pixel camera during 1986 and 1987. High-resolution observations using this instrumentation were taken on a regular basis beginning in 1988. Inversions of the frequency-splitting coefficients derived from these observations confirmed the existence of the SSL. More recently, the 60-Foot Tower data were used to study the solar torsional oscillations and the solar cycle dependence of both the intermediate- and high-degree p-mode frequencies during Solar Cycles 21, 22, and 23. Observations from this program were also employed in ring-diagram studies to demonstrate the existence of helical flows within the SSL. Observations obtained with the 60-Foot Tower's imaging program between 1988 and 2009 are now being employed in a retrospective study of internal zonal and meridional flows during Cycles 22 and 23. Finally, the 60-Foot Tower has also been operated in a non-imaging mode as one of the stations of the BiSON Network since 1992.
Back to Volume