Sea surface temperature perturbations and atmospheric rivers over the western North Pacific

Youichi Kamae, University of Tsukuba, Tsukuba, Japan and Wei Mei, University of North Carolina at Chapel Hill, Department of Earth, Marine and Environmental Sciences, Chapel Hill, United States
Over the mid-latitudes, narrow water vapor transports associated with extratropical cyclones often cause great socio-economic impacts through heavy rainfall and flooding when they make landfall on west coasts of continents. The water vapor bands called atmospheric rivers (ARs) are transient features of global hydrological cycle. In addition to North America and Europe, AR behavior and its role in regional hydrological cycle has extensively been studied over other regions including the western North Pacific. Using an atmospheric reanalysis and ensemble simulations of high-resolution atmospheric general circulation model, we identified that large-scale sea surface temperature (SST) perturbations over the Pacific and Indian Oceans are the keys for AR activity over the western North Pacific. Anomalously-enhanced moist southwesterly produces more frequent occurrences of ARs and heavy rainfall over East Asia in post El Niño years. On interannual-to-decadal timescale, more occurrence of ARs are associated with North Pacific and North Atlantic SST cooling. New insights on the relationship between the large-scale SST and AR activity obtained through these studies may improve seasonal predictability of natural disaster risk over the mid-latitudes.