This paper presents results for key AR-related metrics (AR frequency, duration, and seasonality) based on 20+ different AR identification and tracking methods applied to MERRA v2 reanalysis data from January 1980 through June 2017 as a part of the Atmospheric River Tracking Method Intercomparison Project (ARTMIP). Comparison across the different methodologies are quantified in the context of AR climatology.
Making sense of AR metrics in the literature is at the heart of ARTMIP. The various methodologies produce differences in AR climatologies and, consequently, differences in the impacts attributable to ARs. These differences produce uncertainty in operational weather research and forecasting, water management, and climate projections, which require a current baseline of AR climatology and impacts to assess future changes. Datasets produced from ARTMIP are publicly available (via Climate Data Gateway doi: 10.5065/D6R78D1M) and can be used by other scientists for their own AR research.
We show that AR frequency, duration, and seasonality exhibit a wide range of results, while the meridional distribution of these metrics along selected coastal (but not interior) transects are quite similar across methods. Furthermore, methods are grouped into criteria-based clusters, within which the range of results is reduced. AR case studies and an evaluation of individual method deviation from an all-method mean highlight advantages/disadvantages of certain approaches. Finally, this paper concludes with a discussion and recommendations for those conducting AR-related research to consider.