Gary develops global three-dimensional time-dependent computer models to study
the structure and dynamics of the interiors of planets and stars.
He developed the first in this series of models in the early 1980s to study the
solar dynamo. He wrote a modified version of this model for pre-flight studies
and post-flight analyses of a rotating fluid dynamics experiment
flown aboard NASA Space Shuttles in 1985 and 1995. In his
studies of geodynamics he has simulated global circulation and convection
in the Earth's atmosphere, mantle and core.
He has also simulated convection and magnetic field generation
in the deep interiors of giant gas planets like Jupiter and Saturn.
One of Gary's favorite projects has been his study of the
magnetohydrodynamics of the Earth's fluid iron core, i.e., the
geodynamo.
This is the mechanism that maintains the geomagnetic field via the interaction of
the effects of convection and planetary rotation.
His computer simulations span millions of years,
using an average numerical time step of 15 days. At the surface of the
model Earth, the simulated magnetic field has an intensity, a
dipole-dominated structure, and a westward drift of the non-dipolar structure that
are similar to the Earth's. The model's solid inner core rotates slightly
faster than the surface of the model Earth; this computer modeling result in
1995 served as a prediction for the Earth that continues to be studied via
seismic analyses. Several spontaneous reversals of the simulated magnetic field's
dipolar polarity also occur in the simulations, similar to those seen
in the Earth's paleomagnetic record.
Gary and his former graduate student, Tami Rogers, studied the
solar dynamo
using her spectral computer code.
Their simulations illustrate how internal gravity waves in the sun's deep
radiative interior could be excited by turbulence in the outer convection zone.
Gary and his former graduate student,
Martha Evonuk, studied
giant-planet dynamos
using her finite volume code.
Their dynamo simulations of the deep interior dynamics of a giant planet
maintain a latitudinally banded surface zonal wind profile similar to those
seen on the surfaces of Jupiter and Saturn. The simulations also display
banded patterns of the resulting magnetic field and gravity field at the surface.
Gary and his former graduate student,
Darcy Ogden, studied the supersonic multiphase dynamics of explosive
volcanic eruptions
using a library of computer codes, CFDLib, from the Los Alamos National Laboratory.
Their volcanic simulations predict oscillating fluid flow profiles within the
erupting column.
Gary, Francis Nimmo and their former graduate student,
Erinna Chen, studied circulations and induced magnetic fields in the
subsurface oceans
of Europa and Titan driven by tidal potentials using
3D magnetohydrodynamic simulations.