Seasonal variation of the land-sea breeze circulation in the Pearl River Delta region

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.