Climatology of the planetary boundary layer height over China and its characteristics during periods of extremely temperature

Abstract

Planetary boundary layer height (PBLH) plays a significant role in air quality and climate change. At present, there is a lack of study that focuses on the PBLH characteristics with high spatiotemporal resolution and the subregional variation over China. In this study, we investigated PBLH climatology and its relationship with meteorological parameters across China from 2000 to 2020 using the ERA5 datasets. The PBLH varied diurnally and peaked between 14:00 and 16:00 Beijing Time at an average height between 0.8 km and 1.5 km. The seasonal characteristics of the PBLH also varied among regions. In most regions, the PBLH at urban sites is highest in spring and summer, and lowest in autumn and winter. Interestingly, the PBLH at most urban sites in East China was highest in autumn and lowest in spring. Spatially, in warm seasons (spring and summer), the PBLH showed a strong north-to-south gradient. PBLH was positively correlated with temperature at 2 m, wind speed at 10 m, sensible heat flux, and latent heat flux at most urban sites. However, PBLH was negatively correlated with relative humidity, as well as with surface PM2.5 concentrations. The vertical profiles of PM2.5 and PBLH exhibited an opposite trend that the lower PBLH was accompanied by higher PM2.5 concentration below PBLH at the same time on different days both at Qingshen and Rongchang Stations. In addition, we investigated the relationship between high and low temperatures and PBLH, and found that most sites have a positive correlation between high and low temperatures and PBLH, while coastal cities have a negative correlation between PBLH and low temperatures. We further explored the PBLH characteristics during two periods of extremely high temperatures in July and August 2022 in the Sichuan Basin and extremely low temperatures in the north of Northeast China in January 2023. Compared with the same months during 2011–2020, the PBLH at 16:00 BJT in July (August) increased significantly with 0.68 km (1.24 km), 0.38 km (1.06 km), and 0.69 km (0.89 km) in Chengdu, Chongqing and Yibin, respectively. During the period of extremely low temperature, compared with the corresponding period of the past decade, the PBLH decreased by 45 m (23% reduction), 100 m (37% reduction) and 70 m (16% reduction) at Mohe, Qiqihar and Jixi sites. This study helps to better understand the characteristics of PBLH in China, and it can also provide a reference for studies focusing on the evolution of atmospheric boundary or changes in air quality under the background of climate change.