Presenter: Xiaohui Ma (Ocean University of China)

Description:
Atmospheric rivers (ARs) are closely related with extratropical cyclones and responsible for over 90% of poleward water vapor transport in the midlatitudes. Although evidence is mounting that midlatitude mesoscale sea-surface temperature (SST) anomalies associated with fronts and ocean eddies can influence extratropical cyclones and storm tracks at far distance, few of existing studies explore the potential influence of mesoscale SSTs on ARs. Using high-resolution climate models and observations, we demonstrate that mesoscale SSTs along the Kuroshio Extension can exert a remote influence on landfalling ARs and related heavy precipitation along the West Coast of North America. Inclusion of mesoscale SST forcing in the simulations results in approximately a 40% increase in landfalling ARs and up to a 30% increase in heavy precipitation in mountainous regions and this remote impact occurs on subseasonal-to-seasonal time scales. We find that the presence of mesoscale SSTs can enhance AR genesis by increasing moisture transport associated with extratropical cyclones even though cyclone intensity remains unchanged. It is further demonstrated that the presence of mesoscale SST induced by eddies (fronts) enhances (suppresses) landfalling ARs and associated precipitation, indicating a cancelling role of oceanic fronts and eddies in remotely forcing ARs.