The effect of Chinese Gigacity on weather fronts

Abstract

<p>The rapid, large-scale urbanization in northeast China during the last few decades has been unique. Recently, Kulmala <em>et al</em> (2021) proposed that in eastern China, a cluster of individual megacities, located roughly inside a triangle Beijing-Xian-Shanghai, could be classified as one huge continuous urban area – a gigacity. In a such gigacity region, combined effect of pollution, vast area of increased surface roughness and urban heat island can strongly interact with the local, synoptic, and even continental scale meteorological conditions. Therefore, the complex interactions between multi-scale meteorological processes and the anthropogenic effects of gigacity bring great challenges to the understanding of environmental and climate systems, air quality forecast and weather prediction in the gigacity region. There are many studies about the interaction of urban areas and local and regional scale atmospheric circulation. However, it is still poorly understood how these very large urban areas interact with meso- and synoptic-scale meteorology. The objective of this study was to analyse the effect of gigacity area to the weather fronts. The study period was 1980-2010 when most of the rapid urbanization occurred in the gigacity region. The identification of weather fronts was performed following the principles by Jenkner et al (2010) and Berry et al (2011). However, we further developed the method to utilize the higher resolution of ERA5 data, whereas previously it was using the ERA-Interim data with coarser resolution for front identification (0.25° v.s. 2.5°, respectively). In addition, to identify the key chemical and physical processes, and to quantify their individual contributions, the mesoscale Weather Research and Forecasting (WRF) model coupled with chemistry and the urban canopy model (WRF–UCM–Chem) was used for individual case studies. Based on the results, a statistically significant decreasing trend on number of cold fronts was found in large areas inside the gigacity, most likely due to the increasing surface frictional drag caused by the increasing surface roughness over the very large gigacity area. <span>The results gained in this study will improve the understanding of the gigacity climate and will potentially have strong implications for air quality and weather forecasting in this region.</span></p><p> </p><p>Berry et al., Geophys. Res. Lett. 38, L04809, 2011.</p><p>Jenkner et al., Meteorol. Appl. 17, 1–18, 2010.</p><p>Kulmala et al., Atmos. Chem. Phys. 21, 8313–8322, 2021.</p>