Heat Transport by Atmospheric Rivers under Global Warming: Projections using a High-Resolution Earth System Model

Tuesday, December 10, 2019 - 14:25
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Atmospheric rivers (ARs) are well known for transporting moisture from the tropics into higher latitudes. However, our understanding of heat and energy transport through ARs is limited, despite well-established knowledge of energy transport by baroclinic eddies. Using the high-resolution Community Earth System Model (CESM), we explicitly compute heat transport by atmospheric rivers and assess their impact for two regions that experience high AR landfalls, i.e. western North America and western Europe. Atmospheric rivers are often considered a sub-category of the broader extratropical storm phenomena, one that couples the dynamics of baroclinic waves with significant moisture transport from lower latitudes. Therefore, to evaluate AR’s impact on heat transport, we focus on sensible and latent heat only.

Our approach is to 1) validate high-resolution CESM with MERRA-2 re-analysis data, 2) quantify heat transport via AR, and 3) address how and why these measures change under global warming. CESM is a fully coupled, sophisticated earth system model that allows for feedbacks between the atmosphere, ocean, land, and cryosphere and includes biogeochemical processes. The atmosphere and land employ spectral element dynamical core at a horizontal resolution of ~0.25o, and are coupled to a ~1o irregular grid for the ocean and sea ice. Integrating CESM at high horizontal resolution is necessary to obtain the most accurate AR metrics, especially for regions impacted by topography, as well as to assess AR impacts. ARs are tracked and identified using 3-hourly data for MERRA-2 data, and 6-hourly for CESM ensemble simulations. Heat transport quantities are computed with daily data for both datasets.

There is large uncertainty across different tracking methodologies for AR metrics, such as frequency, especially for future climate scenarios. Therefore, we apply the Atmospheric River Tracking Method Intercomparison Project (ARTMIP)’s Tier 1 MERRA-2 data to bound the uncertainty for heat transports by atmospheric river during the modern era, before computing them for CESM simulations. Our analysis shows that ARs are import vehicles for not only water, but heat transport, and we find that future changes are dependent both on locale and the underlying mechanisms governing them.

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