A New Quarter-degree Global Atmospheric Rivers Database Based on ERA5, 1940–2022

Atmospheric rivers (ARs) are narrow, elongated, synoptic jets of water vapor that play important roles in the global water cycle and regional weather/hydrology. The need for characterizing and understanding AR life cycles (i.e., from genesis to termination) and their variations between different regions motivated the continual development of an AR tracking algorithm suitable for global studies, namely, Tracking Atmospheric Rivers Globally as Elongated Targets (tARget). The algorithm identifies AR objects at individual time steps based on thresholding integrated water vapor transport (IVT) and other requirements, and tracks each AR object in time and space. Building on three previous versions of the algorithm, this paper discusses further refinements to the algorithm since the last release in 2019, to better handle ARs in tropical and polar areas where the background climate is different from the midlatitudes, as well as “zonal” ARs (those with weak poleward IVT or even equatorward IVT) which the previous versions of the algorithm are not designed to capture. The further refined algorithm is applied to the ERA5 reanalysis over 1940–2022 at 6-hour intervals and a 0.25° × 0.25° horizontal resolution. The AR detection result is evaluated based on four analyses: (1) comparison of AR defining characteristics to those of Zhu and Newell (1998); (2) comparison of AR landfall dates in western North America, Britain, and East Antarctica with AR detection methods independently developed in other studies for those regions; (3) comparison of AR durations with ground observations of 91 AR events during 2004–2010 from an AR observatory in northern California; and (4) comparison of AR width and total IVT across the AR width with dropsonde observations of 21 ARs over the northeastern Pacific during 2005–2016.