Influence of Long-Term Trends in Tropical Pacific Sea Surface Temperature on Atmospheric River Statistics in Western North America

Atmospheric rivers (ARs) play a critical role in driving precipitation in Western North America. Understanding their response to variations in tropical sea surface temperatures (SSTs) is essential in the context of a warming climate, especially given the emergent discrepancy between observations and coupled climate models in long-term trends in tropical Pacific SSTs. This study examines AR responses to prescribed La Niña and El Niño-like SST scenarios through ensemble simulations conducted with the Community Atmosphere Model version 6 (CAM6). We use an AR detection algorithm developed by Daemon Kennett (2021) to classify ARs in both CAM6 simulations and the ECMWF Reanalysis version 5 (ERA5) dataset. Initial analysis suggests that CAM6 is underestimating the number of ARs compared to ERA5, possibly due to differences in horizontal resolution. We will discuss implications of this model bias for the detection and attribution of historical changes in AR statistics. The anticipated findings will advance our understanding of how shifts in tropical SSTs influence AR activity and intensity when superimposed on external radiative forcing from greenhouse gases and aerosols, shedding light on how these dynamics may evolve under future climatic conditions, particularly along the U.S. West Coast.