In the simplest description, the Earth is like a giant, three-layered onion, starting from the mantle at the top (an visco-elastic shell approximately 2900 km in thickness), the liquid outer core (~ 2300 km thick) in the middle, and the solid inner core at the center of the Earth. The structure of the Earth can be much more complex if all thermal, chemical and mechanical differences within the Earth are taken into consideration.

        The three layers are not static: they not only change on various time and spatial scales according to their own physical laws, but also interact closely with each other and, together with distinct geodynamic systems on and above the Earth's surface, form a very dynamic Earth. For example, driven by internal radiogenic heat the mantle is in convection, with heat emitting out of the core-mantle boundary (CMB). The amount of heat convected through the CMB to the surface of the Earth via mantle convection on timescales up to 109 years dictates ultimately the secular cooling of the Earth, which, in turn, determines the solidification of the inner core and the convection in the fluid outer core. On timescales as short as several years, the mantle and the inner core can be approximated as solids: their solid body rotations are controlled by core-mantle and inner core-outer core couplings that result from convection in the outer core.

       For generations, solid Earth scientists have being striving to understand the dynamic Earth from inside out. Supported by the NASA Solid Earth and Natural Hazard (SENH) and NSF Math/Geophysics programs, we focus our research on the understanding of the dynamical processes in the fluid outer core, core-mantle interactions, and the consequences in surface geodynamic observables and global changes of the Earth. In particular, we study the following problems:

• How is the convection in the fluid outer core sustained in the history of the Earth? How do the mechanical, compositional and thermal variations in the mantle and in the inner core influence core flow on various timescales?
• As a geodynamo, how does the core flow generate and maintain a strong magnetic field? What are the possible physical processes responsible for the observed geomagnetic secular variation and reversal of the magnetic polarity?
• How does the outer core interact with the mantle and the inner core? What are the consequences of the interactions on the Earth's rotation?
• What are the contributions of the core dynamics to surface geodynamic observables, such as time-variable gravity and surface deformation?
• Could we predict geomagnetic secular variation and assess its significance to space weather?

      For these goals, we developed a numerical core dynamics model called the Modular, Scalable, Self-consistent, and Three-dimensional (MoSST) model, which simulates the core dynamics together with surface geomagnetic/geodynamic/geodetic observations. There are many researchers from various institutions who have been part of our team in joint studies of the scientific problems. In this NASA web site, we provide the current version of MoSST's source code, application programs for numerical data analysis, and samples of scientific results from our MoSST model in publications and presentations as available.