Modeled interaction between the subseasonal evolving of the East Asian summer monsoon and the direct effect of anthropogenic sulfate

A regional climate model is used to conduct four experiments to reveal the interaction between the subseasonal evolving of the East Asia summer monsoon (EASM) and the direct effect of anthropogenic sulfate. One of the experiments is conducted without the emission of anthropogenic SO2. The other three are carried out with the 1, 1.5, and 2 multiples of the SO2 emission of 2000, respectively. The model results suggest that in the rainfall, wind, and circulation of the EASM, the changes caused by the direct effect of anthropogenic sulfate on subseasonal time scale are within the model variability. The change of the EASM rainfall is not sensitive to sulfate forcing on subseasonal time scale but sensitive to the forcing on seasonal time scale. Moreover, rainfall change in the forcing experiments is significantly less (greater) than zero to the south (north) of the EASM rainfall centers on subseasonal time scale, but the EASM rainfall phase is not changed. The rainfall change associates with the correspondingly significant increase (decrease) of the atmospheric stability induced by the forcing of sulfate direct effect. The direct effect of sulfate plays different roles in different stages of the EASM subseasonal evolving. In the early stage, the EASM is significantly enhanced in terms of the interaction between tropical and midlatitude atmosphere. In the late stage, the EASM is weakened in terms of the large-scale atmospheric circulation. Lastly, the responses of the rainfall, wind, and circulation of the EASM to the linear changes in the SO2 emission are nonlinear.