Improved Scaling and Impact Metrics for Pan-Atlantic Atmospheric Rivers

Abstract Atmospheric rivers (ARs) are essential components of the global water cycle, significantly impacting regional pre- cipitation patterns and extreme weather events. Existing AR scales, while valuable, often lack regional specificity, particularly in capturing the nuances of ARs in sub-polar regions. This study addresses these limitations by developing an improved AR scale and impact metrics tailored to the Pan-Atlantic region. Using high-resolution reanalysis data and the Bayesian AR Detector (BARD), the research analyses AR characteristics, highlighting the contrasts between Pacific and Atlantic ARs. Recognizing the limitations of the current AR scale developed by the Center for Western Weather and Water Extremes (CS), the study introduces the Uppsala University (UU) AR scale (NS), specifically designed for the Pan-Atlantic region. The NS incorporates a lower IVT threshold, equal weights for all categories, and a 72-hour persistency, reflecting regional AR behaviour better. The study proposes alternative impact metrics- the AR Severity Index (ARSI), AR Severity Index Kinetic (ARSIK), and a Risk Index- to provide a more comprehensive assessment of AR impacts. These refined metrics and the region-specific NS enhance understanding of AR impacts in the Pan-Atlantic region, contributing to improved forecasting, disaster preparedness, and water resource management.