Abstract
The Mei-Yu front is a significantly important summer precipitation system in eastern Asia. In recent years, anthropogenic air pollution over the Yangtze-Huaihe region of China has been aggravating continuously. A cloud-resolving model coupled with an idealized frontal model is used to investigate the response of aerosols on the Mei-Yu frontal precipitation. The results indicate that increasing droplet concentrations lead to significant precipitation enhancement with the current pollution levels in Mei-Yu frontal system. Under the polluted conditions, the enhanced cold-cloud process is of great importance. Moreover, with the “towing” of active cold-cloud process, cold-cloud and warm-cloud processes developed mutually. These account for the complicated and special microphysical mechanism for aerosol impacts on Mei-Yu frontal system. Furthermore, two types of “microphysical-dynamic positive feedback loop” caused by the interactions of various physical processes and effects (direct dynamic effect, frontogenesis effect, and vapor pump effect) can be found in the Mei-Yu precipitation, which in turn reinforce the microphysical processes. The combined effect is to increase Mei-Yu front precipitation. The interaction of microphysical processes and dynamic processes, and the positive feedback loops they create are the main physical mechanisms behind the significant impacts of aerosol on Mei-Yu frontal precipitation. This may also be an important feature of climate change in eastern Asia.
Highlights
Air pollution has become a global environmental problem, because of its great adverse impact on human health and the climate [1]
In order to distinguish it from the DDE, we suggest that the indirect dynamic effect may be referred to as the second type of dynamic effect—frontogenesis dynamic effect (FDE)
The impact of polluted (P-case) conditions versus typical (C-case) continent conditions on an ideal Mei-Yu front was simulated via Weather Research Forecasting (WRF) coupled with a bulk two-moment microphysics scheme [63]
Summary
Air pollution has become a global environmental problem, because of its great adverse impact on human health and the climate [1]. If no ice nuclei are present, it is believed that anthropogenic air pollution can suppress precipitation, because high aerosol concentrations increase CCN while reduce cloud particle sizes and lead to a narrow droplet spectrum that inhibits collision-coalescence processes [17,18,19,20,21,22,23]. Lynn et al [31] used the mesoscale model to study deep convection clouds in Florida and found that, compared to clean environments, polluted conditions with mid to high concentrations of CCNs experienced delayed precipitation events, vigorous convection development, and increased peak precipitation rate, but decreased cumulative precipitation. Scholars turned to examine some synoptic-scale systems, like frontal systems They found that precipitation reduced slightly near the front but increased farther northward as aerosol concentration was increased [37,38].
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