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| 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. |
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