The ARTMIP Polar Synthesis: A comparative analysis of polar atmospheric river tracking methods in historical and future climate states

Atmospheric rivers (ARs) are the conduit for the majority of atmospheric moisture transport into the polar regions and influence the evolution of the polar ice sheets and sea ice. Their impacts on the polar cryosphere are expected to intensify as atmospheric moisture content and temperatures increase in a warming climate. In order to assess these polar AR impacts, some method for identifying ARs in reanalysis and/or model datasets must be chosen. Prior studies facilitated by the Atmospheric River Tracking Method Intercomparison Project (ARTMIP) show that quantitative and qualitative conclusions about the global climatology, impacts, and future changes of ARs depend on the choice of AR detection tool (ARDT) used in the analysis. There is a community need for a similar comparison of ARDTs in the polar regions (both the Arctic and Antarctica), where the unique atmospheric conditions require different parameters for AR detection relative to global ARDTs.

In this presentation, we report initial findings from the ARTMIP polar synthesis project, a collaborative effort to provide community guidance on best practices for ARDT selection in polar studies. This project builds upon the existing ARTMIP framework to curate and compare AR catalogues from a number of ARDTs that have been developed for polar AR identification. We first analyze polar AR climatology across ARDTs in the historical record using MERRA-2 atmospheric reanalysis, focusing on similarities and differences among ARDTs linked to their algorithm design. These historical catalogues are also used to analyze how differences in AR detection across ARDTs affect interpretation of ice sheet and sea ice impacts. We then extend our analysis to future AR projections by applying each ARDT to three members of the CESM2 large ensemble under the SSP3-7.0 emissions scenario. We focus on cross-algorithm differences in AR detection and associated cryosphere impacts that may be accentuated by future atmospheric warming and moistening. Finally, we use a subset of four ARDTs in a case study to assess how existing ARDTs may be tuned to more accurately identify polar ARs.