Future Changes of the Eddy Moisture Convergence in Winter Over Coastal Lands in Eastern North America and East Asia

Previous studies have shown that increasing moisture convergence by transient eddies will cause winter precipitation increase in the future over the coastal lands in Eastern North America (ENA) and East Asia (EA). Using moisture budget and composite analyses, we investigate the physical processes responsible for the change of eddy moisture convergence and compare them between the two regions. We find that in addition to the “wet get wetter and dry get drier” (“WWDD”) thermodynamic effect, changes in eddy moisture advection cause enhanced eddy moisture convergence north of 30°N and divergence to the south, with magnitudes comparable to the “WWDD” effect in these regions. The north-south dipole pattern is reflected in the precipitation change of drying over the southern coastal lands in the future climate. It is caused by enhanced downgradient eddy moisture transport in the north and upgradient eddy moisture transport in the south, which is explained by the locations of the maximum magnitude of eddy relative humidity in conjunction with increase of mean saturation specific humidity. The eddy dynamic intensities associated with extreme precipitation events are found to increase in the future, contributing to the increase of eddy moisture convergence, but it plays a secondary role. The strong similarities of the underlying processes of eddy moisture change between ENA and EA suggest robust response of the spatially varying role of eddies in impacting future change of regional precipitation in ENA and EA.