Campus Directory: Behnam Seyed Mahmoud

University of Lethbridge

Behnam Seyed Mahmoud
Physics and Astronomy
Office: SA9344
Phone: (403) 329-2360


B.Sc., Physics, University of Lethbridge (AB), M.Sc., Geophysics, Memorial University (NL), Ph.D., Physics, York University (ON)


Geodynamics, Geodynamo, Wobble, Nutation, Elliptical Instability, Planetary Magnetic Field, Fluid Core, Earth Rotation

Research Areas

Theoretical/computational and experimental studies in rotating fluids; Computational techniques to predict the modal frequencies and eigenfunctions of rotating fluid bodies

Previous Research Areas

Oscillatory Dynamics; Elliptical Instability; Planetary Dynamo; Inertial Modes; Gravity Modes; Fluid Core;

Office Hours

By appointment, 9:00 AM to 5:00 PM

About Me

I study vibrations of large liquid bodies such as the Earth's fluid core. These vibrations may be excited as a result of a large earthquake or the gravitational pull of the Moon and the sun. Most stars also vibrate due to external and internal mechanisms. In the experimental geodynamics lab we also study some of these vibrations experimentally. To learn more about my research have a look at some of the articles and interviews about my work.

I am always interested in graduate students who have a strong background in Mathematical and Computational Physics.


Selected Publications

B. Seyed-Mahmoud and Y. Rogisted, Rotational modes of Poincare Earth models, 2021, Geophysical & Astrophysical Fluid Dynamics, 0, pages 1-26

Md. Kamruzzaman and B. Seyed-Mahmoud, Inertial modes of an Earth model with a rotating compressible fluid core and elastic mantle and inner core, 2019, J. Geodesy, 94

B. Seyed-Mahmoud, M.G. Rochester, and C.M. Rogers, Truncation effects in computing free wobble/nutation modes explored using a simple Earth model, 2017, Geophys. J. Int., 209, 1455-1461

B. Seyed-Mahmoud, A. Moradi, M. Kamruzzaman and H. Naseri, Effects of density
stratification on the frequencies of the inertial modes of the Earth's fluid core, 2015, Geophysical Journal International 202, pages 1146 - 1157

Behnam Seyed-Mahmoud and Ali Moradi, Dynamics of the Earth's fluid core: implementation of a Clairaut coordinate system, 2014, Physics of the Earth and Planetary Interiors, 27, 61-67

J. Arkani-Hamed, B. Seyed-Mahmoud, K. Aldridge and R. Baker, Tidal Excitation of Elliptical Instability in the Martian Core: Possible Mechanism for Generating the Core Dynamo, 2008, Journal of Geophysical Research, 113, E06003, Doi:10.1029/2007JE002982

Behnam Seyed-Mahmoud, John Heikoop and Refah Seyed-Mahmoud, Inertial modes of a
compressible fluid core model, 2007, Geophysical and Astrophysical Fluid Dynamics, 101, 489-505

Behnam Seyed-Mahmoud, Michael Rochester, Dynamics of rotating fluids described by scalar potentials, 2006, Physics of the Earth and Planetary Interiors, 156, 143-151

Selected Creative Works

We have developed a new set of equations describing the linearized dynamics of a rotating, self gravitating, stratified, compressible, inviscid fluid body by an exact description in terms of three scalar fields which are constructed from the dilatation, and the perturbation in pressure and gravitational potential.

We have developed computational tools in computer software to solve the above mentioned equations in order to predict the modal frequencies and eigenfunctions of rotating fluid bodies. We have successfully implemented these techniques to compute the modal frequencies of rotating planets and stars.

We have designed and built an apparatus, simulating planetary and stellar bodies, which we use to excite the normal modes of a rotating sphere and spherical shell.

We have also designed and built a PIV (Particle Imaging Velocimetry) system with the camera and the laser module in the rotating frame of the fluid so that when at solid body rotation, there is minimum particle motion relative to the camera. The camera takes a digital video clip of a horizontal plane of the rotating fluid. The clip is transmitted to a computer where the consecutive pictures are correlated, using PIV software, and a velocity field is mapped. The PIV software was modified from the original version developed by the Coriolis Group in France.

Research Interests

My research deals with theoretical/computational and experimental studies in rotating fluids with applications to planetary and stellar interiors. I am interested in predicting the frequencies of the Earth's normal modes, especially those of wobble and nutation for which the observed frequencies are known. By matching the predicted and observed frequencies and adjusting the Earth models for a better fit, we strive to improve our knowledge of the material properties of the Earth's interiors and hence help predict the future states of our planet.

We also investigate the elliptical instability developed in the planetary fluid cores, as a result of the gravitational pull of nearby bodies, in the nonlinear regime. The onset of the elliptical instability has been studied extensively using the linearized equations. It is suggested that the instability may have energized and sustained the geodynamo. Recently we have proposed that the Mars' dynamo, which was responsible for the magnetic field frozen in the planet's crust, was also energized by an elliptical instability developed as a result of the gravitational pull of a giant asteroid orbiting Mars early in the planet's history. Eventually the asteroid crashed into Mars and the planet's dynamo diminished. A planetary dynamo based on elliptical instability has never been established. Our goal is to first solve the nonlinear equations of the instability. This will yield the growth rate of the instability and the amplitude of the motion, in the nonlinear regime. We will then derive a numerical planetary dynamo. In the absence of convection in the planetary fluid cores the above-mentioned dynamo theory offers an alternative explanation for the origin of the planetary magnetic fields.

I am also interested in the experimental studies of these phenomena.

Current Research and Creative Activity

TitleLocationGrant InformationPrincipal InvestigatorCo Researchers
Dynamics of the Earth University of Lethbridge, Lethbridge AB NSERC, $17,5000, extended 2 years; 2015.

High Resolution Magnetic Observations of Mars Enabled by Nanosatellite Technology (MOMENT) Canadian Space Agency, $249,862, 2006.

Jafar Arkani-Hamed (UofT) Keith Aldridge (York U); Robert Zee (UofT)

Previous Research

TitleGrant AgencyCompletion Date
Oscillatory dynamics of rotating fluid bodies: applications to Earth and stellar interiors NSERC 2008
Oscillatory dynamics of rotating stars University of Lethbridge Research Fund 2008
Three potential description of the Oscillatory dynamics of rotating fluids University of Lethbridge Research Fund 2006

Curriculum Vitae


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