Colloquium # 268

A Nearly Incompressible Description of Low-Frequency Turbulence

By Professor Gary P Zank
Distinguished Professor and Director,
Center for Space Physics and Aeronomic Research,
University of Alabama, Huntsville, USA

On Tuesday, Feb 7th at 3PM in Seminar Hall.

The theory of nearly incompressible magnetohydrodynamics (NI NHD) was developed largely in the early 1990’s together with an important extension to inhomogeneous flows in 2010. Much of the focus in the earlier work was to understand the apparent incompressibility of the solar wind and other plasma environments, and the relationship of density fluctuations to apparently incompressible manifestations of turbulence in the solar wind and interstellar medium. Further important predictions about the “dimensionality” of solar wind turbulence and its relationship to the plasma beta were made and subsequently confirmed observationally. However, despite the initial success of NI MHD in describing fluctuations in the solar wind, a detailed application to solar wind turbulence has not been undertaken. Here, we use the equations of NI MHD to describe solar wind turbulence, rewriting the system in terms of Elsasser variables. Distinct descriptions of 2D and slab turbulence emerge naturally from the Elsasser formulation of NI MHD, as do the nonlinear couplings between 2D and slab components. For plasma beta order 1 or less regions, distinct predictions for 2D and slab spectra result from the NI MHD description, and predictions for the spectral characteristics of density fluctuations can be made. We conclude by presenting a NI formulation describing the transport of turbulence throughout the solar wind, including low plasma beta environments such as the solar corona. A comparison of theory and observations in the solar wind is presented.

About the speaker

Professor Gary P Zank is currently an Eminent Scholar and Distinguished Professor and Director of the Center for Space Physics and Aeronomic Research at the University of Alabama at Huntsville. He is also the Chair of Department of Space Science at the University of Alabama at Huntsville. Professor Zank's major research interests are space and solar physics, plasma physics and computational physics.
Professor Zank completed his undergrad (BSc Hons) in 1983 and graduate studies (PhD) in 1987 from University of Natal, South Africa followed by a stint of Post-doctoral studies in Max-Planck-Institut fuer Kernphysik and Max-Planck-Institut fuer Aeronomie (Germany) (1987-1989), Bartol Research Institute, University of Delaware (1989-1991).
Prior to the current position, Professor Zank has been Pei-Ling Chan Chair of Physics and Chair of Physics Department, University of Alabama in Huntsville, Chancellor’s Professor of Physics and Astronomy, University of California, Riverside (UCR) and Director, UCR Institute of Geophysics and Planetary Physics (IGPP) (July 2001 - June 2008) and  System-wide Director, IGPP (September 2005 – June 2008); Professor, Bartol Research Institute, University of Delaware (1991-2000).
Professor Zank is an oxford Medal winner, a Fellow of American Geophysical Union, a Fellow of American Physical Society, a Fellow of the American Association for Advancement of Science. As a young physicist he has also won numerous awards including the prestigious Zeldovich medal as well as NSF Young Investigator Award.
Professor Zank has over 500 publications in space physics, solar physics, plasma physics and astrophysics, over 12000 citations and counting. Apart from being an associate editor of the Journal of Plasma Physics, he has been a member of more than two dozen national and international committees and forums related to Space Plasmas.