Sensitivity of Tropical Cyclone Track Simulation over the Western North Pacific to Different Heating/Drying Rates in the Betts–Miller–Janjić Scheme

Abstract

Abstract The Weather Research and Forecasting Model is employed to examine the sensitivity of simulated tropical cyclone (TC) motion and associated intensity of the western Pacific subtropical high (WSPH) to different heating and drying rates in the Betts–Miller–Janjić (BMJ) cumulus parameterization (CP) scheme. A case study of Tropical Cyclone Megi (2010) is performed. Results indicate that the simulated WPSH strengthens as the heating/drying effects of the BMJ decrease. A strong WPSH subsequently leads to changes in the large-scale steering flow in its southern edge and delays the northward turning of the simulated storm. The associated physical mechanism is revealed. As the heating/drying is overestimated in the BMJ, the model produces unrealistic drying below 500 hPa whereas the atmosphere becomes moist above 500 hPa. Drying in the lower troposphere hinders the activation of the microphysics while moistening in the upper troposphere facilitates the microphysics. As a result, the model generates extensive anvil clouds that extend far away from the TC center and reach the upper troposphere over the WPSH. This leads to a warming in the upper troposphere due to condensation in the anvil clouds, and a cooling in the lower troposphere due to precipitation evaporation below the anvil clouds. Subsequently, the WPSH weakens and the large-scale steering flow becomes anomalously northward, leading to an early recurvature of TC Megi. Results of this study emphasize the importance of a correct representation of anvil clouds in simulating the WPSH and TC track. This study also implies that correcting the heating/drying can be an effective way to reduce errors in simulating the WPSH and TC motion.