Extreme Surface Winds during Atmospheric Rivers: The Modulating Role of Near-Surface Stability

Atmospheric rivers (ARs) are thin and lengthy jets of water vapor responsible for transporting moisture away from the tropics and towards the poles. According to Zhu and Newell (1998), ARs account for over 90% of total poleward water vapor transport at mid-latitudes while only covering ~10% of the earth’s zonal circumference at these latitudes. ARs, when striking landfall, may also bring strong winds and heavy precipitation (Waliser and Guan 2017). While there have been numerous studies performed regarding precipitation relating to ARs and it’s impacts, such as on flooding and water resources (Guan et al. 2010, Dettinger et al. 2011, Neiman et al 2011, etc.), comprehensive examinations of extreme winds in ARs have been lacking. In this study, a global AR database (Guan and Waliser 2015) over the period of 1980–2016, along with relevant fields from the MERRA2 reanalysis, is used to better understand atmospheric conditions conducive to driving extreme surface winds in ARs. Near-surface atmospheric stability and total integrated water vapor transport are analyzed to quantify their relationships to surface winds based on multivariate regression. Multiple regions across the globe where notable number of AR landfalls occur, such as the US west coast, Europe, South America and New Zealand, are analyzed to understand the geographical variations in these relationships. Preliminary findings show that the lower level vertical thermodynamic stability over the ocean near the landfall region is a key predictor in determining extreme surface winds under AR landfalling conditions, with less stable conditions leading to higher surface winds. A better understanding and quantification of atmospheric conditions favorable for the occurrence of extreme surface winds during ARs has implications to improved situational awareness and forecast of the variety of impacts associated with these potentially hazardous events.