| dc.description.abstract | From autumn to the following spring season, the atmospheric circulation of Taiwan is dominated by the Asian continental anticyclone system. Due to mountain blocking, western Taiwan, often experiences low wind speeds and strong subsidence, leading to serious PM2.5 problems. In addition, the planetary boundary layer (PBL) evolutions strongly affect air pollution dispersions. This study explored the characteristics of PBL through the analysis of daily observed sounding data located in northern Taiwan (Banqiao), eastern Taiwan (Hualien), and western Taiwan (Magong). The analysis was conducted according to different synoptic weather patterns including (1) prevailed by the northeasterly monsoonal flow; (2) under the influence of high-pressure peripheral circulation, and (3) weak synoptic weather conditions.
According to the analysis results of the sounding profiles, the average thickness of the northeast monsoon is about 1600m in Taiwan. Banqiao is obviously affected by easterly winds in the northeast monsoon weather in winter. Hualien has obvious radiation inversion near the surface at 00 UTC in winter and the wind speed is significantly higher in the northeast monsoon weather. Due to the strong northerly wind, the potential temperature and specific humidity of the lower layer in Magong are mixed well. In the weak synoptic weather, Banqiao and Hualien have more obvious sea-land breeze circulation. The winter sea breeze in Taiwan starts from 10:00 to 11:00 in the morning and lasts for 8 to 9 hours.
Comparing the sounding observation profiles of Taiwan during the winter of the El Niño year and the La Niña year. The results show that there is a strong southerly wind in the lower troposphere around Taiwan during the El Niño. During the La Niña, the wind direction of the near-surface layer is more northerly and the location of the continental cold high is more northerly, which makes the easterly and northerly winds stronger.
When the easterly wind is stronger in the winter, the sedimentation effect on the lee side area of Taiwan is enhanced, which is unfavorable for the diffusion of atmospheric pollutants. The strengthening of the northerly wind will bring more foreign pollutants to Taiwan, resulting in poor average air quality. | en_US |