The role of air-sea interactions in atmospheric river events: Case studies using the SKRIPS regional coupled model

Atmospheric rivers (ARs) are narrow, elongated plumes of enhanced water vapor transport over the oceans. In the extratropical regions, ARs play a key role in water vapor transport and are responsible for the extreme precipitation and flooding events, especially in the western United States. Since ARs play such an important role, improved understanding and accurate forecasts of ARs and AR-induced precipitation are critical. In the present work, a regional coupled ocean-atmosphere model is used to hindcast the ARs in January 2018. We investigate the impact of air-sea interactions on the ocean and on modeling the ARs by comparing a series of coupled and uncoupled model simulations initialized on every day of the month. During the first three weeks in January, with relatively cold ARs over warm ocean, the coupled model captures strong upward latent heat flux associated with ARs and reproduces the observed SST cooling; after the first three weeks, during ARs with warm air over cold ocean, the coupled model captures the SST warming in the AR region. By considering the air-sea interactions, the coupled model simulates the integrated water vapor (IWV) and integrated vapor transport (IVT) better than the uncoupled model. The simulated IWV is improved by about 12% according to the Brier skill score (BSS). For IVT, which is far more variable, the improvement is 6%. The improved skill is greater (approximately 20% for IWV and 12% for IVT) when the SST cooling is greater than 0.5 degree Celsius during the AR events.