Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh11b..06g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH11B-06
Astronomy and Astrophysics
Astrophysics
[7522] Solar Physics, Astrophysics, And Astronomy / Helioseismology, [7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7544] Solar Physics, Astrophysics, And Astronomy / Stellar Interiors And Dynamo Theory
Scientific paper
The rotation profile of the solar interior, as observed by helioseismology, exhibits a sharp transition at the base of the convection zone. Above the radiative-convective interface, strong differential rotation is observed while the radiative zone itself is in near-uniform rotation. To date, the only self-consistent published model of the dynamics of the transition region, the solar tachocline, is the one proposed by Gough & McIntyre (1998). In this model, large-scale meridional flows are "gyroscopically pumped" by the differential rotation in the convection zone, down-well into the radiative zone where they encounter a large-scale primordial magnetic field. The magnetic field is thereby confined by the down-welling flows within the radiative zone only, and imposes the observed differential rotation. In this talk, I review a series of new results inspired by this original idea, each of which provides insight into a different aspect of the problem. The new picture which emerges from these related explorations clarifies many outstanding issues, and provides guidance for future investigations. These results begin with a study of the angular-momentum balance of the radiative interior (Garaud & Guervilly 2009), assuming the presence of a confined magnetic field and neglecting the role of meridional flows (a model which is identical to the one originally proposed by Ruediger & Kitchatinov, 1997). We show analytically that this model systematically fails to explain the observed value of the rotation rate of the radiative zone. This implies that, within the Gough & McIntyre model framework, the dynamics of the convection zone flows in the tachocline are crucial not only for field confinement but also for angular-momentum transport. We then present an exhaustive study of a toy model for gyroscopic pumping of large-scale meridional flows by the solar convection zone (Garaud & Acevedo-Arreguin 2009), which 1. illustrates the phenomenon pedagogically 2. quantifies the conditions under which these large-scale flows may or may not enter the radiative zone 3. provides predictions for the amplitude of the flows in the solar radiative zone in the absence of an embedded large-scale magnetic field, as functions of the forcing and of the local conditions in the tachocline. Our conclusions confirm that gyroscopically pumped flows could indeed have strong enough amplitudes to confine a large-scale primordial field beneath the solar tachocline, but only under certain conditions which were not previously recognized. Moreover, they provide guidance on to how to design numerical experiments of the Gough & McIntyre model for numerically achievable values of the governing parameters. Finally, they also provide insight into the possible dynamics of a younger, more rapidly rotating Sun. Guided by the aforementioned results, we conclude by revisiting the Gough & McIntyre model numerically and comparing model predictions with observations of the solar tachocline.
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