Advanced coupled atmosphere-wave-ocean modeling for improving tropical cyclone prediction models

We will discuss the progress in developing a physically based coupled atmosphere-wave-ocean framework for the next generation tropical cyclone research and operational models as a route towards skillful prediction of TC intensity and structure. This project is conducted by a team of scientists from academia and government organizations under the auspices of the NOAA's Hurricane Forecast Improvement Project (HFIP) and Navy's National Ocean Partnership Program (NOPP). The key element of our approach is an air-sea interface module consisting of a wave boundary layer model and an air-sea heat and momentum flux budget model that explicitly resolve wind-wave-current interaction processes and sea spray effects.

Scientific and technical challenges in designing the air-sea interface module in tropical cyclone conditions will be discussed, with a particular focus on the effects of breaking waves and sea sprays. Breaking waves may significantly modify the air-sea momentum flux. They cause airflow separation behind breaking wave crests and become responsible for most of the air-sea momentum flux in very young developing seas. Wave breaking limits the steepness of smaller waves and their contribution to the form drag. Sea sprays, generated in great amount by surface breaking waves in high winds, may reduce the near surface atmospheric boundary layer turbulence, leading to reduced friction at the air-sea interface. However, it is difficult to accurately quantify this effect because of the large uncertainty in the spray generation function.