Abstract
Observations indicate that late-summer precipitation over the East Asian transitional climate zone (TCZ) showed a pronounced decreasing trend during 1951–2005. This study examines the relative contributions of anthropogenic [including anthropogenic aerosol (AA) and greenhouse gas (GHG)] and natural forcings to the drying trend of the East Asian TCZ based on simulations from CMIP5. The results indicate that AA forcing plays a dominant role in contributing to the drying trend of the TCZ. AA forcing weakens the East Asian summer monsoon via reducing the land-sea thermal contrast, which induces strong low-level northerly anomalies over eastern China, suppresses water vapor transport from southern oceans and results in drier conditions over the TCZ. In contrast, GHG forcing leads to a wetting trend in the TCZ by inducing southerly wind anomalies, thereby offsetting the effect of the AA forcing. Natural forcing has a weak impact on the drying trend of the TCZ due to the weak response of atmospheric anomalies.
Highlights
This study shows that 3 out of the 32 CMIP5 models can capture the observed decreasing trend of the latesummer TCZ rainfall
It remains unclear whether the ability of the models in reproducing the observed precipitation trend in late summer over the TCZ is attributed to SST biases in the models
We have examined spatial distribution of the biases in climatological SST in August over 1951–2005 in 32 CMIP5 models relative to the observation (Please see Fig. S2 in the supporting information)
Summary
It is worth noting that the AA forcing can affect large-scale precipitation by modulating the atmospheric circulation but can alter the local precipitation via microphysical cloud processes, as indicated by previous studies[35,36,37]. We speculate that the increase in local AA emissions may be partly responsible for the precipitation decrease over the TCZ. This issue will be further explored in our future studies.
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