The Annual Modes of Tropical Precipitation Simulated with LASG/IAP AGCM: Sensitivity to Convection Schemes
积云参数化方案对热带降水年循环模态模拟的影响

The annual modes of tropical precipitation are simulated with a Spectrum Atmospheric General Circulation Model (SAMIL) developed by LASG/IAP. Sensitivity of the model's response to convection schemes is discussed. Two convection schemes, i.e. the revised Zhang-McFarlane (ZM) and Tiedtke (TDK) convection schemes, are employed in two sets of AMIP-type SAMIL simulations, respectively. The major characteristics of the annual mean precipitation can be reasonably reproduced in both simulations. There are some uniform simulation biases when using the ZM and TDK schemes. Both of them show bad performance in the simulation of spring-fall asymmetric mode. The simulated Indian monsoon and northern Australian monsoon are weaker, while the western North Pacific, African and American monsoons are stronger than the observations. The simulated bias of monsoon mode is derived from the simulation of the western North Pacific (NWP) precipitation in the boreal summer. In the boreal summer, the simulated temperature with both the schemes is cooler than that from the NCEP data in the upper troposphere and warmer in the lower troposphere, which results in convective instability in the NWP and heavier precipitation there. The mean temperature from the surface to the tropopause is cooler than the observations in the simulations. It leads to the weaker temperature gradient and weaker westerly jet over the NWP. The weaker westerly jet provides favorable dynamic condition for the convection anomaly over the NWP. Nonetheless, there are also some differencs between the TDK and ZM schemes. The simulated monsoon mode in the western North Pacific is stronger with the ZM scheme than with the TDK scheme. The simulated specific humidity is larger with the ZM scheme than with the TDK scheme. It is one of the reasons that the simulated NWP summer monsoon precipitation is heavier with the ZM scheme. The performance of the SAMIL in simulating the tropospheric temperature and humidity over the NWP deserves further improvement.