Abstract
Abstract. This study examines the role played by aerosol in torrential rain that occurred in the Seoul area, which is a conurbation area where urbanization has been rapid in the last few decades, using cloud-system-resolving model (CSRM) simulations. The model results show that the spatial variability in aerosol concentrations causes the inhomogeneity of the spatial distribution of evaporative cooling and the intensity of associated outflow around the surface. This inhomogeneity generates a strong convergence field in which torrential rain forms. With the increases in the variability in aerosol concentrations, the occurrence of torrential rain increases. This study finds that the effects of the increases in the variability play a much more important role in the increases in torrential rain than the much-studied effects of the increases in aerosol loading. Results in this study demonstrate that for a better understanding of extreme weather events such as torrential rain in urban areas, not only changing aerosol loading but also changing aerosol spatial distribution since industrialization should be considered in aerosol–precipitation interactions.
Highlights
It has been reported that there has been an increase in the frequency of torrential rain in urban areas over the last decades (Bouvette et al, 1982; Diem and Brown, 2003; Fujibe, 2003; Takahashi, 2003; Burian and Shepherd, 2005; Shepherd, 2005; Chen et al, 2015)
The effective sizes of hydrometeors are calculated in a microphysics scheme that is adopted by this study and the calculated sizes are transferred to the Rapid Radiation Transfer Model (RRTM)
This study examines how aerosol affects heavy precipitation in an urban conurbation area
Summary
It has been reported that there has been an increase in the frequency of torrential rain in urban areas over the last decades (Bouvette et al, 1982; Diem and Brown, 2003; Fujibe, 2003; Takahashi, 2003; Burian and Shepherd, 2005; Shepherd, 2005; Chen et al, 2015). Aerosol-induced invigoration and intensification of convection and associated convective clouds raise a hypothesis that the large spatial variability in aerosol in tandem with increasing aerosol loading can generate and enhance torrential rain, which can involve the inhomogeneity of precipitation and associated cloud intensity in urban areas. We select an MCS over the Seoul area (in South Korea) that has a population of ∼ 25 million and is one of the representative conurbation areas around the world These simulations are to identify key mechanisms that are associated with cloud-scale microphysics and dynamics and explain the generation of the inhomogeneity of precipitation and associated torrential rain in terms of the spatial variability and loading of aerosol.
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