[1] The data of a 1-year (2003)(2004) simulation with a finest horizontal resolution of 1.5 km, using the Fifth-Generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5), were analyzed to investigate the seasonal-mean features of the land-sea breeze (LSB) and regional circulation over the Pearl River Delta (PRD) region in southern China. The seasonal-mean diurnal variations reveal the general patterns of the LSB in the four seasons. These small-scale mean flow fields in the region have not been revealed in any previous studies. The results reveal a strong anomalous westerly sea breeze toward the eastern coast of the PRD in the early afternoon that is present in all the four seasons but is particularly strong in autumn and winter and may enhance the low-level convergence in Hong Kong. Furthermore, the condition of the atmosphere in autumn and winter is much more stable when compared with that in spring and summer, which is not favorable for the vertical dispersion of pollutants. The overall effect of these mean meteorological conditions may be an important factor for the generally higher air pollution index observed in Hong Kong during autumn and winter.

ABSTRACT: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.