Understanding the source of seasonal predictability for the winter Atmospheric Rivers

The atmospheric moisture transport plays a significant role in global hydrological cycle. The poleward atmospheric moisture transport is predominantly confined to Atmospheric Rivers (ARs) which form as spatially narrow plumes (500-1000 km wide) that can stretch over thousands of kilometers in the troposphere. ARs transport approximately 90 % of the water vapor from the tropics into the extratropics and often induce heavy wintertime precipitation along the west coast US. Therefore, accurate prediction of ARs on sub-seasonal to seasonal timescales (S2S) is urgent. While prediction skill of ARs beyond 10-days has not been assessed, several recent studies suggest an existence of potential predictability of ARs at S2S timescales by linking the AR activity to ENSO and MJO. To understand the cause of the year-to-year change in AR activity and moisture transport, we have undertaken research to quantify the AR characteristics (frequency, landfall latitude, intensity) and the causes of moisture transport change in different ENSO phases. Multi-model hindcasts are used to examine whether the state-of-the-art climate prediction model simulate the relationship between ARs and ENSO, thus have potential to predict the seasonal AR activity. Seasonal AR prediction skill and model biases are also compared.