[A-AS05] Weather, Climate, and Environmental Science Studies using High-Performance Computing

[AAS05-P05] Case Study on the Characteristics of the Atmospheric Boundary Layer in Taipei and Yilan of Northern Taiwan during Winter

*PEI-DI JENG¹, Jou-Ping Hou¹ (1.Chung Cheng Institute of Technology, National Defense University Environmental Information and Engineering Dept)

Keywords: Northeast Monsoon, Froude number, terrain effect

Taipei Basin and Lan-yang Plain, located in northern Taiwan, exhibit distinct terrain characteristics despite their geographical proximity. Under the influence of the northeast monsoon, significant differences arise between the two regions in terms of near-surface wind field variations, the modification process of cold air over land, and the characteristics of the atmospheric boundary layer at lower levels. These differences highlight the critical impact of terrain on the dynamic and thermodynamic properties of the ambient atmosphere. This study employs the Weather Research and Forecasting (WRF) model to investigate the local atmospheric boundary layer characteristics in Taipei Basin and Lan-yang Plain under northeast monsoon conditions. A four-level nested grid configuration is utilized, with the innermost domain featuring a spatial resolution of 500 m to simulate a case study on November 26, 2021.Both observational data analysis and simulation results indicate that the air temperature in the lower-latitude Lan-yang Plain decreases more rapidly compared to the higher-latitude Taipei Basin. Geographic location and topographic effects at surface observation stations in these two regions lead to marked differences in temperature and relative humidity. Furthermore, the Froude number was calculated at multiple locations on Datun Mountain, situated on the northern side of the Taipei Basin. Results show that at certain periods and locations, the Froude number exceeds 1, allowing the northeast monsoon to flow over Datun Mountain and produce downslope winds within the Taipei Basin. This phenomenon confines precipitation primarily to the windward mountainous areas. In contrast, precipitation in the Lan-yang Plain is not restricted to windward mountain slopes; the plain rainfall is even greater compared to the mountainous windward regions. These findings highlight the influence of varying terrain types under the northeast monsoon.