A theory based on the shallow water equation is developed to explain the generation of moving spiral-banded structures in tropical cyclones. The theory proposes that fluctuation of the vorticity distribution in the compact core region can act as a source, generating gravity waves that produce the banded structures. This mechanism is usually called the Lighthill radiation mechanism. A numerical experiment using the Fifth Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) code is used to test this theory. The moving bands in the simulated tropical cyclone show good agreement with the theoretically calculated gravity waves that emerge from a core region with an elliptical distribution of vorticity. Results of the simulated cyclone also illustrate that spiral cloud bands are triggered by the propagating gravity waves. Abstract A theory based on the shallow water equation is developed to explain the generation of moving spiral-banded structures in tropical cyclones. The theory proposes that fluctuation of the vorticity distribution in the compact core region can act as a source, generating gravity waves that produce the banded structures. This mechanism is usually called the Lighthill radiation mechanism. A numerical experiment using the Fifth Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) code is used to test this theory. The moving bands in the simulated tropical cyclone show good agreement with the theoretically calculated gravity waves that emerge from a core region with an elliptical distribution of vorticity. Results of the simulated cyclone also illustrate that spiral cloud bands are triggered by the propagating gravity waves.

The objective of the present study is to investigate the effect of initial soil moisture in the Tibetan Plateau (ISMTP) during the spring period on the local and regional climate in subsequent months. Numerical experiments with different ISMTP are made from 1 April to 30 June for the year 1998 using a regional climate model. This was a wet year with anomalously high summer precipitation over China. The same experiments have also been done for the year 1995, which was a normal year with respect to the summer rainfall over China. In both years, the snow amount over the Tibetan Plateau (TP) was higher than normal in the preceding winter/spring. The results of the experiments indicated that an increase in the ISMTP may lead to decreases in the air temperature, vertical velocity, and surface heating over the TP in June. In addition to the local effects, an increase in the ISMTP may also lead to modifications of the climate in some remote regions in early summer, such as an increase in the amount of monsoon precipitation over the mid to lower reaches of the Yangtze River region in eastern China and a decrease over the south China region. These precipitation differences due to the changes in ISMTP are consistent with those due to anomalous snow cover over the TP in winter or spring. Physically, the Tibetan High is weakened with an increase in ISMTP, which leads to a change in the strength of the Asian summer monsoon. Copyright © 2007 Royal Meteorological Society

In this study, the fifth‐generation Pennsylvania State University‐National Center for Atmospheric Research Model (MM5) was used to investigate the effects of urbanization on land–sea breezes (LSBs) in the Pearl River Delta (PRD) region, which is a rapidly developing area located in southern China. LSBs in the 2003/2004 winter were simulated utilizing an approach in which the NCEP Final Analysis data averaged in the 2003/2004 winter is used as initial and lateral boundary conditions for the model. The simulated surface winds are shown to be capable of reproducing the basic features and diurnal variation of the LSBs. Sensitivity experiments with changes in land uses were performed with this model. Results of these experiments show that urbanization in the PRD region can have significant effects on the patterns of the LSBs and circulation in the region. In particular, it has been shown that the urbanization of Shenzhen (a major city located in the eastern coast of the PRD and neighbouring to the north of Hong Kong) may significantly enhance the sea breeze to the west of Hong Kong in the early afternoon. This may enhance the low‐level convergence in Hong Kong and may worsen the air pollution problem there. On the other hand, the effects of urbanization in the western coast of the PRD region are relatively local and LSBs on the eastern PRD are generally not affected. Copyright © 2009 Royal Meteorological Society

It is shown in this study that applying some convection suppression criteria to the MIT or Emanuel cumulus parameterization scheme may significantly improve the performance of a regional climate model to simulate the Asian summer monsoon precipitation, particularly the precipitation over southeastern China and the Mei‐yu rainband over the East Asian region. With the original MIT cumulus scheme, the precipitation over the ocean particularly the South China Sea (SCS) region is generally over‐estimated, which may result in the under‐estimation of precipitation over China. It is found that the relative vorticity criterion (which shuts down the convection when the low‐level flow is anticyclonic and stronger than a certain threshold value) has the largest impact on suppressing the over‐estimated precipitation over the SCS.