TYPICAL WEATHER CHARACTERISTICS ASSOCIATED WITH AIR POLLUTION IN HONG KONG AREA

With the hourly data of Air Pollution Index （AP1） by Hong Kong Environmental Protection Department （HKEPD） during the 6 years of 2000 - 2005 and NCEP / NCAR reanalysis data of 2.5°× 2.5° wind and pressure fields, the characteristics of API in Hong Kong area and the impacts of typical weather characteristics on the air pollution in Hong Kong have been studied. The results are shown as follows. （1） The API exhibits obvious seasonal variability as the number of air pollution days increases by the year. For most of the local monitoring stations, it is the most from January to March, a little less from July to September and the least from April to June. （2） There are four typical types of weather situations that are responsible for the air pollution in Hong Kong： tropical cyclones, continental cold highs, transformed highs that have moved out to sea and low pressure troughs.

Numerical Experiment Research of a Marine Fog Event in the Pearl River Estuary Region

A marine fog event that occurred near the Pearl River Estuary region on 26March 2002 was investigated with the fifth-generation Pennsylvania State University/National Centerfor Atmospheric Research Mesoscale Model (MM5). The results of numerical experiment are veryconsistent with the surface observations, especially in the processes of marine fog formation andevolution. Besides, a series of sensitivity numerical experiments were performed by varying thedistribution of landuse type and the turbulence exchange process. It is shown that the marine fogforms along the coastal line. Tests have indicated that when the distribution of landuse type ismodified, the regions where the marine fog can intrude into are obviously different. The turbulenceprocess in the model is important for fog formation and evolution. If the influence of turbulenceprocess is ignored in numerical simulation experiment, the simulated maximum of the cloud liquidwater content and the height of fog top will be decreased greatly.

Wavelet analysis of the convectively-coupled equatorial waves

The spatial and temporal distribution characteristics of the main convectively-coupled equatorial waves were analyzed with the OLR data provided by NOAA and the method of wavelet analysis.The results indicate that the wavelet analysis can effectively distinguish MJO,Kelvin,ER,TD,and EMRG wave and the characteristics of their activities in 1992.The propagation speeds of MJO and ER wave are the slowest,following by Kelvin and TD wave and with MRG the fastest.The MJO from the Indian Ocean to the West Pacific Ocean,the Kelvin wave near the International Date Line,the ER and the TD wave around the West Pacific Ocean and the MRG in the eastern of the International Date Line have the biggest wave amplitude.The MJO in boreal winter and spring,the Kelvin wave in boreal spring and summer,the ER wave in boreal autumn,and the TD wave in boreal summer are active.The WMRG wave activates in boreal autumn,whereas EMRG wave appears year-round.These spatial and temporal characteristics agree well with the results of relevant theoretical studies,indicating that the wavelet analysis in the time-frequency domain is another effective method to reveal the evolution of convectively-coupled equatorial waves.