Abstract
Boundary layer height (BLH) is an important parameter in climatology and air pollution research, especially in urban city. We calculated the BLH with a bulk Richardson number (Ri) method over urban cities of China during 1980–2018 using European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-interim data after carefully validation with sounding data obtained from two meteorology stations in eastern China during 2010–2018. The values of BLH between these two types of data have correlation coefficients in the range of 0.65–0.87, which indicates that it is reasonable to analyze long-term trends of the BLH from ERA data sets. Using ERA-interim calculated BLH, we found that there is an increasing trend in the daytime BLH in most cities of eastern China, particularly during the spring season. A correlation analysis between the BLH and temperature, wind speed, relative humidity and visibility revealed that the variability in meteorological parameters, as well as in aerosol concentrations over highly polluted eastern China, play important roles in the development of the BLH.
Highlights
Planetary boundary layer (PBL) is the turbulent layer of the troposphere and plays an important role influencing the concentration, transport and diffusion of atmospheric compounds (Stull, 1988)
The soundings were usually launched at 08:00 and 20:00 Beijing time (BJT), so the value of Boundary layer height (BLH) were mainly compared at these two moments
The correlation coefficients between two kinds of BLH data were larger than 0.7° at 08:00 for most of the time, which is consistent with earlier results in the Beijing station (Guo et al, 2016)
Summary
Planetary boundary layer (PBL) is the turbulent layer of the troposphere and plays an important role influencing the concentration, transport and diffusion of atmospheric compounds (Stull, 1988). The PBL height is most commonly identified as an inversion in the potential temperature and dewpoint, or as a peak value in the low-level wind speed. The height of planetary boundary layer varies spatially and temporally, typically ranging from about a hundred meters to some kilometres. The PBL height can be as high as 5 km over a desert in mid-summer due to strong surface heating, while being as low as 50–100 m during a night over land under clear sky and light wind conditions (Zhang et al, 2013; Chen et al, 2016).
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