Coupled Observations and Air-Sea Fluxes in Tropical Cyclones: A Key to Advance New-Generation Coupled Model Predictions

Heat and moisture fluxes from the ocean surface are the energy source for tropical cyclones (TCs). However, observations of air-sea fluxes in TCs are very limited, especially in extreme high wind conditions underneath of the eyewall region of a TC. The Impact of Typhoon on the Ocean in the Pacific (ITOP) field campaign has provided an unprecedented data set to study the air-sea fluxes in TCs and their impact on TC structure and intensity. More than 800 GPS dropsondes and 900 AXBTs/AXCTs as well as drifters and floats were deployed in TCs from August-October 2010, including Typhoon Fanapi and Supertyphoon Megi with a record peak wind speed of more than 80 m/s. This study focuses on the characterization of spatial and temporal variation of air-sea fluxes in TCs. It is found that the air-sea fluxes are quite asymmetric around a storm with complex features representing various air-sea interaction processes in TCs. A unique observation in Typhoon Fanapi is the development of a stable boundary layer in the near-storm cold wake region. Both the observations and coupled atmosphere-ocean model forecasts show that the near surface air in the stable boundary layer tends to penetrate further inward into the TC inner core region and the eyewall than the air in unstable and neutral boundary where some high theta-e air goes into rainbands. It shows that the cool-SST induced stable boundary have a direct impact on TC structure and intensity. The coupled observations observed from ITOP and other field campaigns such as the Coupled Boundary Layer Air-Sea Transfer (CBLAST) over the Altantic provide valuable data sets for development, evaluation, and verification of fully coupled atmosphere-ocean models for TC prediction. This talk will present both the coupled observations and high-resolution coupled model verifications.