Effects of the Northeast Monsoon on Different Terrain of the Taipei Basin and Lanyang Plain in Taiwan

The Taipei Basin (TPB) and the Lanyang Plain (LYP) are geographically similar, both situated in northern Taiwan. However, significant differences in heat transfer processes arise between the two regions due to local terrain influences under the Northeast Monsoon. Precipitation patterns in the TPB and LYP, especially during the case study of 26 November 2021, differ markedly due to the distinctive dustpan-shaped terrain of the LYP. Our study, based on the WRF model, reveals that while both the TPB and LYP are characterized by downward cold air transfer, the TPB exhibits stronger atmospheric boundary layer mixing and a higher mixing layer height compared to the LYP. Turbulent kinetic energy (TKE) in the TPB is higher during the morning and evening, while vertical heat flux is more pronounced in the LYP. The average sensible heat flux is greater in the TPB, whereas latent heat flux is higher in the LYP. In addition, the amount of water vapor transported into the LYP by the Northeast Monsoon is greater than in the TPB. In the TPB, the wind field, influenced by the terrain, shifts predominantly from northeast to northeasterly and southeasterly. However, upon entering the LYP, the same environmental wind field is affected by the dustpan-shaped terrain, resulting in a counterclockwise near-surface wind pattern. The wind field transitions from northeasterly in the north to westerly, southwesterly, or northwesterly in the south. This difference in wind field causes precipitation in the TPB to be confined mainly to the windward side of the mountainous areas whereas, in the LYP, precipitation occurs both on the windward side and, more abundantly, in the plains. The effect of different types of terrain under the Northeast Monsoon is quite obvious.