Measuring Meridional Circulation - ABSTRACT
The meridional circulation in the solar convection zone is an
axisymmetric flow in the meridional plane of the Sun. In contrast to the
prominent differential rotation, which is the axisymmetric component of
the longitudinal flow, the meridional circulation is more difficult to
measure, as it is much weaker than the differential rotation.
Measurements of the meridional surface flow revealed large temporal
variations around a mean pole-ward flow of ~20 m/s. Some measurements
also exhibit a multiple cell structure including regions with flow
components directed towards the equator.
In order to understand the physical role that the meridional circulation
is expected to play in the solar magnetic dynamo process, the whole
convection zone (depth ~200 Mm) needs to be probed for this flow by
helioseismology.
Theoretically, the influence of the meridional flow on the solar
oscillations is well understood. And based on theoretical studies the
meridional circulation could in principle be probed by global
helioseismology. However, the effect on the global oscillation modes is
very small and difficult to disentangle from rotation and other
influences. Therefore up to now, only local helioseismology was
successful in deriving information on the strength and the structure of
the meridional circulation. However, the information on the meridional
circulation was only inferred down to depths of ~15 Mm. The various
results are not in perfect concordance. Nevertheless, these
investigations also find a large temporal variation and a complex
structure of the flow in the solar interior as in the case of the
surface measurements.
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URLs:
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--
Dr. Markus Roth
Kiepenheuer-Institut für Sonnenphysik
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