Spray modification to the marine atmospheric boundary layer
One problem our group is working on is evaluating the role of sea spray in near-surface sensible and latent heat flux. Does adding water droplets to the lower marine atmospheric boundary layer enhance heat and moisture transferred from the sea to the air? For hurricane forecasting, this question is critical, so we take a fundamental approach by coupling Lagrangian particles to direct numerical simulation of turbulence. When each individual particle can exchange momentum, heat, and water mass with the surrounding fluid, we can learn a great deal about the physical importance of transfer in these types of multiphase systems which play such a large role in weather and climate systems.

Particle-laden turbulence

Enthalpy fluxes estimated from within tropical cyclones
At very high winds, such as those found within hurricanes and tropical cyclones, accurate measurements of air-sea fluxes are notoriously difficult to obtain. As a result, observational data is scarce. Therefore, in addition to the numerical simulations performed in our group, we have recently begun to estimate surface thermodynamic fluxes using dropwindsonde data (More on dropsondes, NOAA Hurricane Research Division) obtained from over 2000 profiles taken from within over 30 tropical storms over the past 20 years. This project ultimately seeks to strengthen our confidence in existing high-wind flux measurements as well as provide insight into the role of sea spray under these extreme conditions.

CK versus U10
Enthalpy flux coefficient versus 10-meter wind speed. From Richter & Stern, Geophysical Research Letters, 2014

Turbulence intermittancy and sediment transport
The movement and transport of bedload sediment is strongly determined by coherent structures and intermittancy of the turbulent flow above. Using direct numerical simulation and large eddy simulation techniques coupled with an interacting particle discrete element method, we investigate the small-scale mechanisms responsible for initiation and duration of individual particle movement, with the goal of developing upscaled statistical descriptions of resting and flight times based on the characteristics of the surrounding turbulence. This work is done in collaboration with the Pontifical Catholic University of Chile and the Naval Research Labs - Stennis Space Center.

Direct Numerical Simulation combined with the Discrete Element Method used to study sediment transport and intermittancy at the bed of turbulent channel flow