Air-Sea Coupling and Boundary Layer Structure in Tropical Cyclones

Air-sea interaction in Tropical Cyclones (TCs) through surface momentum and heat fluxes is controlled by the disequilibrium of thermal and dynamic processes not only at the air-sea interface but also in the atmospheric boundary layer (BL) and the upper ocean. Unlike the marine BL under calm wind conditions, the BL in TCs is highly three-dimensional and inhomogeneous. One of the most prominent ocean responses is the storm-induced cold wake that locates in rear-right quadrant of the TC track, which can produce pronounced asymmetry in the TC BL. Observations from Impact of Typhoon on the Ocean in the Pacific (2010) shows that the BL over the cold wake is stable while it is neutral to unstable everywhere else in Typhoon Fanapi (2010). Numerical simulations from a coupled atmospheric-ocean model suggests that this stable BL suppresses the atmospheric moist convection downstream of the cold wake and modulate the near-surface TC inflow over the cold wake, which is important for TC intensification. Co-located GPS dropsonde and AXBT data and the coupled model simulation of Typhoon Fanapi will be used to investigate the dynamic and thermodynamic processes associated with the stable BL and their impact on TC structure and intensity.