IGPP Seminar Series

Modeling the global-scale solar dynamo and predicting the Sun's ``climate''

by Dr. Mausumi Dikpati
High Altitude Observatory

Abstract

Unlike Earth's dipolar magnetic fields, solar magnetic fields consist of wide ranges of length-scales and strengths, and interestingly, they evolve in a cyclic fashion with a 22-year periodicity. A magnetohydrodynamic dynamo operating in the Sun is most likely responsible for producing the solar magnetic activity cycle. In this talk I will present a global-scale solar dynamo of flux-transport type, which involves three basic processes: (i) generation of toroidal fields by shearing the pre-existing poloidal fields by differential rotation (the $\Omega$-effect), (ii) re-generation of poloidal fields by lifting and twisting the toroidal fluxtubes (the $\alpha$-effect), and (iii) flux transport by meridional circulation. This class of dynamos has been successful in explaining many large-scale solar cycle features, including a particularly difficult one -- the correct phase relationship between the equatorward migrating sunspot belt and the poleward drifting large-scale, diffuse fields. The meridional flow plays a key role in determining the dynamo cycle period as well as the memory of past magnetic fields. We will present the successes of flux-transport dynamos, including their predictive capability compared to so-called precursor methods. We will close by presenting our timing and amplitude predictions for upcoming cycle 24.
Tuesday, 24 April 2007
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM