The Atmospheric River Tracking Method Intercomparison Project

Atmospheric rivers (ARs) are long and narrow regions of intense, vertically-integrated water vapor transport (IVT) that contribute significantly to high-impact weather events and hydroclimate. While the AMS has recently adopted a qualitative definition of ARs into the Glossary of Meteorology, many differences in AR identification and tracking methods exist as a result of surging interest in this topic. These differences lead to uncertainties regarding the AR climatology, the relationship between ARs and precipitation, and how these may be altered under future climate change scenarios. The primary goal of the Atmospheric River Tracking Method Intercomparison Project (ARTMIP) is to quantify the uncertainties that arise purely as the function of a diverse set of AR identification and tracking methods.

The ARTMIP seeks to address key science questions by dividing them broadly into “Tier 1” and “Tier 2” projects. The Tier 1 project involves all participants implementing their AR identification and tracking methods on a common data set (MERRA; Jan 1980 through Apr 2017) and producing output for the same metrics (AR frequency, duration, intensity, etc). These results will then be used to facilitate a quantitative evaluation of the uncertainties in these metrics that arise from using different AR identification methods. Tier 2 describes a set of analyses that will encompass sensitivity studies regarding differences in resolution, reanalysis, and future climate change scenarios. ARTMIP is currently in the Tier 1 Phase and will begin Tier 2 in 2018. Preliminary metrics and analysis from Tier 1 will be presented.