Ocean Fronts and Eddies Remotely Forcing Atmospheric Rivers and Heavy Precipitation
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AbstractAtmospheric rivers (ARs) are responsible for over 90% of poleward water vapor transport in the midlatitudes and can produce extreme precipitation when they make landfall1-2. However, despite of recent improvements, weather and climate models still have difficulty simulating and predicting the timing and location of landfalling ARs and associated extreme precipitation3-5, highlighting the need to better understand AR dynamics. Here, using high-resolution climate models and observations, we demonstrate for the first time that mesoscale sea-surface temperature (SST) anomalies associated with the Kuroshio front and eddies can exert a remote influence on landfalling ARs and related heavy precipitation along the West Coast of North America. Inclusion of the 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. The modeling results further show that this remote impact occurs within two weeks, implying the potential influence of the dynamical processes on AR predictability at subseasonal-to-seasonal time scales. A proposed mechanism for the influence of mesoscale SST forcing on ARs is the asymmetrical response of the atmosphere to warm vs. cold mesoscale SSTs over the eddy-rich Kuroshio Extension region, which results in a net increase of moisture flux above the planetary boundary layer, prompting AR genesis via enhancing moisture transport into extratropical cyclones in the presence of mesoscale SST forcing.
