Internal Rotation: Detailed Specifications
Team Coordinator: Jesper Schou
Data Requirements
All available normal-mode frequencies:
all frequencies up to maximum degree from Dynamics Program;
from the Structure Program (using the 5kbs telemetry channel)
complete mode coverage in l and m up to some value of l,
with selected l and m, including sectoral modes, at higher degrees.
For non-standard analyses (e.g., looking for departures from
axisymmetry) power spectra and associated fitting parameters
(e.g. linewidths) will be used.
Science Objectives
The goal is to measure the Sun's internal rotation rate as a function of
latitude and depth, over as great an extent of the solar interior as
possible, with the normal-mode frequencies available from SOI.
The Sun's internal rotation and any other asphericities
split the otherwise-degenerate frequencies of
normal modes of the same (n,l) multiplet.
The Internal Rotation TSWG will use the
splitting arising from rotation: this is antisymmetric in m, provided
that the Sun has a unique axis of symmetry. The measurement of the
internal solar rotation will constrain theories of angular momentum
transport in stellar interiors. In particular,
measuring the rotation in the
deep interior will determine whether the Sun has a fast-rotating core,
which might be a relic of the Sun's faster rotation as a young star if
the transport of angular momentum from the core is relatively inefficient.
The determination of the
rotation within the Sun's convective envelope will permit direct
comparison with models of rotating, convective shells and with
experimental realizations of such systems.
Turbulent compressible convection constrained by rotation is
likely to possess ordered structures and circulations, involving
coherent plumes and vortices, large-scale mean flows and zonal jets.
The inversion of the rotational splitting may therefore
reveal
jets and other pronounced shearing flows as components of
the differential rotation profile both within the
convection zone and in a region of penetration below.
Over the period of the mission, it is also our intention to
utilize the continuous coverage in time to track temporal
changes that may occur in the global rotation pattern.
It has been suggested from studies of flare activity that the deep
interior of the Sun may rotate about an axis different from the
axis of rotation inferred from the observed surface rotation. Rotation
about a non-unique axis would give rise to hyperfine structure in the
power spectra that would not be present if the Sun were purely axisymmetric.
Such hyperfine structure might in principle be seen directly in the
power spectra; on the other hand, if it were unresolved, it would contribute
to the apparent linewidth and its presence might then be inferred from the
apparent linewidths and fitted mode amplitudes. We shall therefore use
power spectra and mode linewidths and amplitudes, in addition to the
mode frequencies, to search for the signature of rotation about a non-unique
axis.
These effects will have to be disentangled from
the effect of structural and magnetic asphericities,
which will be considered by the Internal Structure TSWG.
Thus close collaboration between the two teams is foreseen.
This page last reviewed 14 Aug 1995
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