Air-sea coupling and tropical cyclone prediction in the Australian region

Air-sea coupling has been investigated with respect to prediction of tropical cyclone (TC) intensity change and the ocean response in the Australian region. The coupled research model comprises the Australian Bureau of Meteorology's tropical cyclone limited area prediction system (TC-LAPS) and a regional version of the BLUElink ocean forecasting system. A series of case study forecasts and a coupled ensemble, using an inertial coupling method, show that in each of the cases, the use of re-analysed sea surface temperatures significantly improves the prediction of TC intensity change in the intensification phase. The results also show that dynamic air-sea coupling has a modest impact on intensity in cases where storm induced SST cooling is significant and is likely to be important for predicting the rate of TC intensity change and peak intensity in these cases. No negative impact was found for cases where SST cooling was not a significant factor. The results highlight the relative increased complexity of coupled tropical cyclone prediction in the Australian region compared to other regions and the importance of having skillful component models, a data assimilation system and initialization of correct sea-level pressure, SST and upper ocean heat content. To address the issue of providing reliable ocean initial conditions, a limited-area data assimilation system and a nonlinear dynamical initialization scheme have been developed for the coupled limited-area model (CLAM). The initialization method provides significant improvements over current methods for both introducing information and minimizing discontinuities in the dynamical prediction system.