Atmospheric River Forward Speed: Variability, Trend, and Genesis Analysis using NASA ModelE and CYGNSS

Atmospheric rivers (ARs) are elongated bands of water vapor transport in the atmosphere, which can generate extreme precipitation upon making landfall. As global warming projections indicate more intense ARs in the future, understanding AR characteristics in different regions can be useful in interpreting precipitation trends and assessing climate change threats. As part of an ongoing project to analyze atmospheric river genesis and moisture transport variability, the NASA GISS-E2.1 climate model is used to identify and track ARs from 1980-2020. The focus of the work herein is the forward speed of the centroids for AR footprints as they evolve in time. As a first step, this work calculates the statistics of slow and fast-moving ARs, defined as events whose lifetime forward speed is in the high or low tail of the distribution for all ARs in the region of interest. Focusing on ARs over the Pacific Ocean basins, separately for each hemisphere, we investigate trends, frequency of occurrence, interannual variability, and the geographic distribution of slow and fast ARs. The atmospheric conditions during genesis, with a focus on surface winds using CYGNSS, are analyzed for slow and fast AR events in order to identify predictive characteristics causing these specific AR dynamics. Finally, the slow and fast AR events are assessed in terms of the precipitation they generate at landfall, to understand if forward speed influences the impact of the ARs.