Atmospheric rivers in the PETM: Importance for cool season precipitation

Abstract:

For the modern era, atmospheric rivers (ARs) are an important component of Earth’s hydrological cycle, serving as a critical water delivery mechanism for cool season precipitation around the globe. ARs are long, narrow filamentary structures that transport and distribute copious amounts of moisture from lower latitudes poleward. They can act either as drought busters supplying much needed precipitation, typically, along the west coast of continents, or fall into the extreme category and serve as impetus to catastrophic floods. For the Paleocene Eocene Thermal Maximum (PETM), approximately 55 million years ago, these relationships appear to hold. We present results from a series of high-resolution PETM simulations that test different greenhouse gas and orbital forcing configurations. We employ the Community Earth System Model (CESM) at a horizontal resolution of ~25km which is forced with climatological sea surface temperatures supplied by equilibrated, fully coupled PETM experiments. The characteristics of ARs and their relationship to precipitation are evaluated along with the underlying dynamical mechanisms, and we show that frequency and location of landfalling ARs can be closely tied to cool season precipitation. We focus on landfalling ARs over western North America, European, and Australian continents, and illustrate that proxy evidence located in the Pyrenees supports this conclusion (Chen et al., 2018).

Reference: Chen, C., Guerit, L., Foreman, B.Z. et al. Estimating regional flood discharge during Palaeocene-Eocene global warming. Sci Rep 8, 13391 (2018). https://doi.org/10.1038/s41598-018-31076-3.