Dynamic And Thermodynamic Contributions To Northern China Dryness In El Nino Developing Summer

In El Nino developing summer, Northern China shows reduced precipitation. The underlying mechanism is investigated through an analysis on the regional moisture and moist static energy budget. It is shown that the thermodynamic effect in relation to water vapour changes increases the regional wetness, but it is much smaller than the dynamic effect in relation to anomalies of atmospheric circulation. The anomalous vertical descent term is particularly pronounced. This anomalous vertical motion is mainly constrained by the horizontal advection of climatological moist enthalpy by anomalous wind, with a deficit of moist static energy in the region. A descent is then produced to compensate the energy lose and leads to dryness. Further investigation shows that an El Nino-induced anomalous cyclone over Northeast Asia is the main ingredient in controlling the dynamic effect for both water vapour budget and moist static energy budget.