Abstract
The sun is a plasma threaded variously by magnetic fields that stretch
from the deep interior to the heliosphere. These fields can couple
various layers together and transfer momentum between different parts of
the solar interior. The sun is not a rigid body and there is no
requirement from conservation of angular momentum that the overall solar
rotation rate as measured at the photosphere need remain constant. At
the 150-foot solar tower telescope on Mt. Wilson the Doppler shift,
magnetic fields and line intensity of the solar photosphere have been
measured as often as possible beginning in 1965 (1965 and 1966 were lost
in a data handling mistake). The overall rotation rate is determined for
each observation by fitting the observed photospheric velocities to the
function ωsid(φ) =A+Bsin2(φ) +Csin4(φ) where φ is latitude, to determine
what is known as the A coefficient. We are currently re-reducing all the
data from the 150-foot tower system. Differential rotation is described
by the B and C coefficients which we are holding constant with average
values. The velocities come from Doppler shifts which with a Babcock
magnetograph come mostly from the displacement of the moving sampling
stage which balances the intensity in the wings of the spectral line.
Line shape calibration uncertainties do not influence this shift. We
find variations in the global rotation rate which are larger than the
shifts known as the torsional oscillations. If the B and C coefficients
are fitted to each Dopplergram the torsional oscillations become
evident. Instrument changes of the exit slit system and spectrograph
grating do not introduce jumps in the A coefficient. Restriction of
observations to those when the sun is within 40 degrees of local noon
leaves the result essentially unchanged. There may be a solar cycle
influence but, the resulting pattern shown in the attached figure is
more complex than that. Data from before 1983 has a scatter about 3
times larger than what is shown here with an average consistent with
these results. However, the larger scatter prevents the variability from
being evident.