dc.description.abstract | Apart from anthropogenic emissions, air pollution also plays an important role in weather patterns. In winter, Taiwan is affected by Asian continental anticyclone system, and the prevailing wind is northeasterly. Under the influence of the northeast monsoon, central and southern regions become stable atmospheric condition, because they are located at the leeside area of Central Mountain Range.
Taiwan atmospheric PBL Observation, Modeling, and Data Assimilation experiments (T-POMDA) took R/V Ocean Researcher 3 to do the experiment from January 1 to 6, 2021, including the casting of sounding balloons, and erected a 10-meter meteorological tower, to collect observed data from sea surface and atmospheric boundary layer. In line with the schedule and track arranged by R/V Ocean Researcher 3, departing from Kaohsiung Port, to the north to outer-sea of central area, and returned to Kaohsiung Port. Due to the influence of the northeast monsoon to the north of Taichung, the sea conditions were poorer, and the observation couldn’t be carried out. The outer-sea of Taichung to Yunlin is the key area of the observation, so the sounding balloons were released more frequently. This paper combines synoptic weather and local weather characteristics to illustrate the vertical structure characteristics of the planetary boundary layer.
During marine observation, affected by the configuration of Asian continental anticyclone system, synoptic meteorological conditions were mainly affected by the northeast monsoon and the structure of continental high-pressure peripheral circulation. When the northeast monsoon prevailed, the coast of KP area presented the characteristic of the weak wind outflow. While in the weather pattern of high-pressure peripheral circulation, due to the barrier of the Central Mountain Range, the wind prevailed easterly, and the wind field of west side was totally weak, the atmospheric diffusion condition was bad, so that could easily accumulate the pollutants. The development of vertical structure of the planet boundary layer is also more important to the diffusion of pollutants in the situation.
At land, the surface is heated by the thermal action in daytime, and the mixing layer develops, the thermal action is strongest at noon, mixing boundary layer height is highest in the day. Through the enhancement of radiative cooling at nighttime, the bottom layer forms stable boundary layer, and the boundary layer height decreases. However, at the ocean, due to the smaller difference of sea temperature, the thermal action won’t be easier to heat the sea surface at noon, and radiative cooling at night and dawn is less obvious, so the diurnal variation of marine boundary layer height is smaller than land.
The analysis results show that central offshore is influenced by Channel Effect, the wind speed is higher, and the thermal action is more obvious. Under the condition of relatively unstable atmosphere, the boundary layer height is higher, and the better pollutants diffusion condition makes PM2.5 concentration lower. However, the southern offshore is located at more leeside area of Central Mountain Range, the synoptic wind won’t be easier to influence the area, the wind speed is lower, and the thermal action is less obvious. The condition of stable atmosphere makes the boundary layer height lower, the unfavorable pollutant diffusion condition makes severe pollution events occurred easily. | en_US |