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A Grand Scientific Challenge: Understanding Solar Convection/Dynamo

Speaker:Dr. Keke Zhang
Affiliation:Center for Geophysical and Astrophysical Fluid Dynamics, Exeter University, UK
Date:September 12, 2008 (Fri)
Time:4:00-5:00 p.m.
Venue:Room 522, 5/F, Chong Yuet Ming Physics Building, HKU


Large-scale solar magnetic activities, such as the 11~year sunspot cycle, are the manifestation of magnetohydrodynamic processes occurring in the deep solar interior. Understanding these MHD processes, incorporating coupling between the solar convection zone and the highly differentially rotating solar tachocline, poses a grand scientific challenge in modern science and astrophysics. We shall discuss the Cowling's theorem and the toroidal flow theorem in multi-layered spherical systems, in attempting to illustrate why the problem is physically and mathematically challenging and complex. We shall also present a three-dimensional spherical solar dynamo based on a finite element method with the three-dimensional tetrahedralization of the spherical system. It will be shown that our nonlinear dynamo model is able to reproduce the main features of the solar magnetic field: an equator-ward propagating dynamo wave, with a period of about 11 years, of dipolar symmetries. Moreover, we shall discuss the future scientific research, primarily driven by new spacecraft observations, on planetary and solar magnetic fields.

About the speaker:

Dr. Keke Zhang, Professor of Astrophysical Fluid Dynamics, obtained his B.Sc. in 1982 from University of Nanjing, China. He obtained both his M.Sc. in 1985 and then Ph.D in 1987 from University of California, Los Angeles, USA. After his PhD, he did post-doctoral research at UCLA, USA (1987-1988) and at University of Cambridge, UK (1989-1992). He has been at University of Exeter, UK, since 1992. His main areas of expertise are in planetary and astrophysical fluid dynamics. His active research has led to about 130 scientific publications in refereed journals like JFM, Science, Nature, PRL and ApJ, as well as to a Cambridge University Monograph on Applied Mathematics and Mechanics, which will be published by Cambridge University Press in 2009. He is currently the director of Center for Geophysical and Astrophysical Fluid Dynamics at Exeter University and he has served as an Editor-in-Chief for Journal of Physics of the Earth and Planetary Interiors since 2004 (a major international journal for planetary physics with Impact factor 2.5).