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**Session 74 - The Quiet & Active Sun.**

*Display session, Friday, January 09*

*Exhibit Hall, *

## [74.06] 2-D Solar Dynamo Models in Spherical Geometry

*J. A. Markiel (U. Rochester)*
We have developed a 2-D finite-difference code for solving the kinematic
mean field dynamo equations in spherical geometry. We apply this
code to the solar dynamo, considering interface dynamo models of the type
initiated by Parker (1993, ApJ 408, 707) but including the full
solar rotation profile as determined by helioseismology.
The regeneration of the poloidal field by the alpha-effect occurs
in the lower part of the convection zone, while the production of toroidal
field by the differential rotation takes place below the convection zone.
The surface rotation rate persists to the
base of the convection zone, where a transition to rigid rotation of the core
takes place within a thin layer of thickness \leq 0.1 R_ødot
below the convection zone. The diffusivity changes discontinuously across
the interface from its large turbulent value in the convection zone to a
smaller uniform value in the core. Diffusivity ratios between
0.001 and 0.1 are considered. Both positive and negative alpha-effect
are allowed, and the growth of the dynamo is limited by a
nonlinear quenching of the alpha-effect based on the ratio of magnetic
to kinetic energy density.

If the shear layer is sufficiently thin so that the radial gradient of the
rotation dominates the latitudinal gradient, then modes propagating
along the interface are produced. The direction of propagation is towards
the equator (pole) if the product \alpha \cdot \partial Ømega/\partial r
is negative (positive), as expected. However, the radial gradient changes
sign at midlatitudes, which has two effects: separate bands of field
are produced in the equatorial and polar regions, propagating in different
directions, and (2) the latitudinal gradient always dominates in the
intermediate region where \partial Ømega/\partial r \sim 0. The latter
effect can produce different types of modes which alter or destroy the
interface modes excited in the rest of the hemisphere.

This research is supported by NSF grant AST-9528398.

The author(s) of this abstract have provided an email address for comments about the abstract: markiel@callisto.pas.rochester.edu

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