Professor Farrell's primary research area is dynamic meteorology. Dynamic meteorologists use physics and mathematics together with numerical simulation to gain fundamental understanding of the motions of the atmosphere. Professor Farrell has been particularly interested in the turbulence of the jet stream and the origin and predictability of cyclones, the low pressure systems responsible for much of the variability in weather. Efforts to understand the process of explosive cyclone development led Professor Farrell and co-workers to deeper understanding of how disturbance evolution occurs in general under the dynamics of fluid flow. Theoretical insights gained from this work has clarified the dynamics of midlatitude and tropical cyclone growth as well as rapid perturbation growth in laboratory flows and conducting fluids.
Turbulence is a fundamental physical phenomenon that continues to elude comprehensive theoretical explanation. The planetary scale jets that form spontaneously from atmospheric turbulence provide striking examples of the phenomenon of order emerging from disorder that characterizes turbulence. Applying methods drawn from stochastic dynamical systems analysis to the turbulence of planetary atmospheres has helped us to advance understanding of how large scale order arises from the chaos of turbulence. This advance provides a physical explanation for the formation of jets from turbulence both in the gaseous planets and in the high latitudes of the Earth's atmosphere. The role of interaction between order and disorder in maintaining the statistical mean turbulent state was also clarified by this analysis providing understanding of how the position and strength of atmospheric jets and associated storm tracks are determined. The heat and momentum transfer between subtropical regions and higher latitudes associated with these storm tracks are fundamental processes regulating the Earth's climate and understanding atmospheric turbulence provides an important insight into how man's intervention is changing Earth's climate.