214 research outputs found
Revisiting the solar tachocline: Average properties and temporal variations
The tachocline is believed to be the region where the solar dynamo operates.
With over a solar cycle's worth of data available from the MDI and GONG
instruments, we are in a position to investigate not merely the average
structure of the solar tachocline, but also its time variations. We determine
the properties of the tachocline as a function of time by fitting a
two-dimensional model that takes latitudinal variations of the tachocline
properties into account. We confirm that if we consider central position of the
tachocline, it is prolate. Our results show that the tachocline is thicker at
higher latitudes than the equator, making the overall shape of the tachocline
more complex. Of the tachocline properties examined, the transition of the
rotation rate across the tachocline, and to some extent the position of the
tachocline, show some temporal variations
The Sun Asphericities: Astrophysical Relevance
Of all the fundamental parameters of the Sun (diameter, mass,
temperature...), the gravitational multipole moments (of degree l and order m)
that determine the solar moments of inertia, are still poorly known. However,
at the first order (l=2), the quadrupole moment is relevant to many
astrophysical applications. It indeed contributes to the relativistic
perihelion advance of planets, together with the post-Newtonian (PN)
parameters; or to the precession of the orbital plane about the Sun polar axis,
the latter being unaffected by the purely relativistic PN contribution. Hence,
a precise knowledge of the quadrupole moment is necessary for accurate orbit
determination, and alternatively, to obtain constraints on the PN parameters.
Moreover, the successive gravitational multipole moments have a physical
meaning: they describe deviations from a purely spherical mass distribution.
Thus, their precise determination gives indications on the solar internal
structure. Here, we explain why it is difficult to compute these parameters,
how to derive the best values, and how they will be determined in a near future
by means of space experiments.Comment: 14 pages, 9 figures (see published version for a better resolution),
submited to Proceedings of the Royal Society: Mathematical, Physical and
Engineering Science
The Rotation Of The Deep Solar Layers
From the analysis of low-order GOLF+MDI sectoral modes and LOWL data (l > 3),
we derive the solar radial rotation profile assuming no latitudinal dependance
in the solar core. These low-order acoustic modes contain the most
statistically significant information about rotation of the deepest solar
layers and should be least influenced by internal variability associated with
the solar dynamo. After correction of the sectoral splittings for their
contamination by the rotation of the higher latitudes, we obtain a flat
rotation profile down to 0.2 solar radius.Comment: accepted in ApJ Letters 5 pages, 2 figure
Rotation of the solar convection zone from helioseismology
Helioseismology has provided very detailed inferences about rotation of the
solar interior. Within the convection zone the rotation rate roughly shares the
latitudinal variation seen in the surface differential rotation. The transition
to the nearly uniformly rotating radiative interior takes place in a narrow
tachocline, which is likely important to the operation of the solar magnetic
cycle.The convection-zone rotation displays zonal flows, regions of slightly
more rapid and slow rotation, extending over much of the depth of the
convection zone and converging towards the equator as the solar cycle
progresses. In addition, there is some evidence for a quasi-periodic variation
in rotation, with a period of around 1.3 yr, at the equator near the bottom of
the convection zone.Comment: 12 pages, 8 figures. To appear in Proc. IAU Symposium 239: Convection
in Astrophysics,eds F. Kupka, I. W. Roxburgh & K. L. Chan, Cambridge
University Pres
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