CEE Seminar -Turbulence, droplets, and hurricanes: Understanding complex physics in the environment

In the environment, air and water transport a wide variety of constituents, including nutrients, pollution, droplets, aerosols, dust, and even bugs. Predicting where these things end up, and in what abundance, is a difficult enterprise; this difficulty impacts a huge range of scientific disciplines, and limits our ability to predict future environmental conditions and engineer solutions. In particular, turbulent motions are a highly nonlinear and small-scale phenomena that form the foundation on which environmental transport is based. Making matters worse, often it is hazardous or simply impossible to observe these motions in nature or recreate them in the laboratory. Here I will focus on one such effort of leveraging high-resolution, high-fidelity simulations to explore complex flows and their accurate representation in coarse-scale models: tropical cyclones and the problem of air-sea interaction. It has long been hypothesized that sea spray generated at the ocean surface plays a large role in the transfer of heat, moisture, and momentum at the air-sea interface. In high winds, it is well-known that spray is produced in abundance, but it is much less clear how spray may mediate air-sea transfer in these conditions. A turbulence and droplet-resolving framework is used as an idealized testbed to examine the assumptions and premises of commonly used bulk spray flux parameterizations. In multiple respects, spray droplets limit their own ability to enhance air-sea heat and moisture transfer due to the complex thermodynamic feedbacks that occur during their exchange with the surrounding air. Ultimately, the primary factors determining whether or not spray can modulate air-sea energy and momentum fluxes are the spray lifetimes and airborne concentrations -- both of which are quantities that are largely unknown or uncertain in high-wind conditions.