A Moist Static Energy Perspective on Atmospheric Rivers

Atmospheric rivers (AR) are well known for their role in the global water cycle, but their role in global energy transport, including sensible heat, has not been well explored. This study uses the moist static energy (MSE) framework, and two leading reanalysis products to diagnose the role of ARs in modulating MSE. This is done through a case study of a well-observed AR, and analysis of a full year in the North Pacific and globally.

We find that moist static energy aggregates on the eastern side of extratropical cyclones, as the cold front sharpens and the AR water vapor intensifies in the cyclone’s warm sector. The aggregation mostly results from the advection of warm and moist air into the warm sector, while radiative and surface flux feedbacks play smaller roles. On the planetary scale, sensible heat fluxes co-located with ARs can reach an annual average of 50PW in mid-latitudes, while occupying only ~10% of the Earth’s circumference.

These results are a first step towards understanding the sensible heat and total energy fluxes co-located with ARs. Local applications of understanding the river MSE fluxes include better parametrizations and predictability of the inland sensible heat transport, which can have important consequences on the erosion and production of the snowpack. Globally, the results underline the interdependence of the heat budget and the hydrological cycle. As the climate evolves, changes in ARs will not only affect the water cycle, but more generally the global energy balance.