Boundary Layer Characteristics Over Complex Terrain in Central Taiwan: Observations and Numerical Modeling

• Published in: Journal of geophysical research. Atmospheres 2022-01, Vol.127 (2), p.n/a
• Main Authors: Cheng, Fang‐Yi, Wang, Yu‐Tzu, Huang, Mu‐Qun, Lin, Pay‐Liam, Lin, Ching‐Ho, Lin, Po‐Hsiung, Wang, Sheng‐Hsiang, Tsuang, Ben‐Jei
• Format: Article
• Language: English
• Subjects: Air; Air flow; Air pollution; Atmospheric boundary layer; Atmospheric circulation; Atmospheric models; Boundary layer structure; Boundary layers; complex terrain; Dimensional analysis; Geophysics; high‐resolution weather simulation; Lower atmosphere; Mathematical models; Metropolitan areas; Modelling; Mountain regions; Mountainous areas; Mountains; nocturnal low‐level jet; Numerical simulations; Planetary boundary layer; Planetary evolution; Pollutants; Pollution dispersion; Resolution; Richardson number; sea breeze intrusion; Sea breezes; Stable boundary layer; Terrain; tethersonde; Tower observations; Variation; Weather forecasting; Westerly flow; Wind; Wind flow
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2021JD035726

The development of the atmospheric boundary layer and flow circulation becomes complicated over complex terrain. A field campaign involving the acquisition of tethersonde, ozonesonde and 10‐m meteorological tower observations was conducted during September 2–8, 2013, over the Puli Basin located in the mountainous area of central Taiwan to investigate the evolution of the planetary boundary layer (PBL) and flow circulation. In addition, numerical simulations using the Weather Research and Forecasting (WRF) model were performed to examine the three‐dimensional air flow variations. Analysis of the tethersonde data indicated a well‐mixed boundary layer structure and a steady westerly flow over the Puli Basin during the daytime that became further enhanced in the afternoon. The 600‐m resolution WRF model simulation showed that the enhanced wind flow in the afternoon was due to the inland penetration of the onshore sea breeze, which also transported high concentrations of O3 from the western metropolitan area into the basin. During the nighttime, a stable boundary layer formed, above which a nocturnal low‐level jet formed throughout the campaign period in the Puli Basin. The WRF model is able to reproduce the general variations in the wind flows and thermal structures. Furthermore, the diagnostic PBL height estimated based on the critical Richardson number provides an enhanced understanding of the evolutionary characteristics of the PBL over complex terrain. Plain Language Summary A field campaign was conducted over the complex terrain in Taiwan to investigate the wind flow and thermal structures in the lower atmosphere. Moreover, a high‐resolution numerical weather model was applied to examine the three‐dimensional air flow variations. Distinct local circulations were identified in the central mountainous area of Taiwan, which further enhances our understanding of the transport and dispersion of air pollutants over central Taiwan. Key Points A field campaign and high‐resolution weather model were conducted over complex terrain to investigate Planetary Boundary Layer (PBL) structure and flow circulation The daytime sea breeze transports concentrated O3 inland, and this intrusion enhances the wind flow over the mountain The PBL evolution processes illustrated in this study provide important information for air quality research