Feedback effect of tropical cyclone on the western Pacific Subtropical high

Friday, 22 April 2016: 1:15 PM
Ponce de Leon C (The Condado Hilton Plaza)
Yuan Sun, Nanjing University of Information Science and Technology, Nanjing, Jiangsu, China

Previous studies indicate that, regional climate models (RCMs) can well reproduce the feature of the East Asian monsoon when tropical cyclones (TCs) are not active over the western North Pacific. In contrast, a large bias often appears in the simulations of the East Asian monsoon when TCs are active over the western North Pacific, which can be attributed to the erratic departure of simulated TC track from their realistic positions. Microphysical parameterization (MP) and convective parameterization (CP) play important roles in determining TC track. Take for example the interactions between Megi (2010) and the western Pacific subtropical high (WPSH) in this study, we analysis the results of sensitivity experiments with different model configurations, and reveal the physical reasons for the erratic departure of simulated TC tracks in RCM simulations, and thus propose a new mechanism that a TC can affect its track through its thermodynamic feedback on the WPSH. The results of this study indicate that, the proper configuration of MP and CP schemes plays a vital role in determining the accuracy of the simulated TC track. Without the proper configuration of the two schemes, the model generates overestimated hydrometeors near the TC eyewall, which extends outward with height following the updrafts in the TC eyewall and thus results in excessive anvil clouds in the upper troposphere. The upper hydrometeors extending from the northern TC fall gradually following the downdraft in the WPSH. As the hydrometeors fall above the freezing level, the continuous condensation warming near the hydrometeors heats the upper troposphere in the WPSH. However, as the hydrometeors fall below the freezing level, the evaporative cooling of the hydrometeors cools the middle and lower troposphere in the WPSH. Such a pattern of vertical temperature distribution causes the decrease of the geopotential height in the middle and lower troposphere under hydrostatic constrain conditions, and thus results in the weakening of the WPSH. Due to the thermodynamic feedback effect of TC on the WPSH, the intensity of the WPSH is decreased continuously. This results in the unrealistic break of the WPSH, and thus the early north-turning of TC, which further contributes to the large bias in simulating the TC track and the WPSH.
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