Circulation responses to regional aerosol climate forcing in summer over East Asia

For East Asia, circulation responses to anthropogenic aerosol radiative forcing dominate aerosol-precipitation interactions. To gain insights, this study analyzed CESM simulated circulation changes related to the north drought and south flood' pattern caused by aerosol increases between two cases. One case was driven by the year-1850 global emission inventory, whereas the other used identical emissions for all regions except East Asia where anthropogenic emissions of aerosols and precursors of the year-2000 were imposed. Results show that the cooling caused by increased aerosols, which peaks at the middle latitudes, induces two intervened anomalous circulations in the troposphere. Near the surface, the increased land pressure weakens the southerlies and reduces the moisture transport for the entire eastern China. Meanwhile, in the free troposphere, the anomalous circulation exhibits remarkable meridional variations. While convergence occurs over 25 degrees-45 degrees N which partially compensates the decrease of moisture transport from lower levels, divergence develops over regions to the north which enhances the moisture deficiency. In addition, the southward shift of the jet stream stimulates anomalous rising and sinking motions over the south and north of 32 degrees N. The combination of these changes leads to precipitation increase in the Yangtze River Valley but decrease over North China.