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Clouds and Radiation in a mock-Walker Circulation
  • Levi Glenn Silvers,
  • Thomas Robinson
Levi Glenn Silvers
Princeton University

Corresponding Author:[email protected]

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Thomas Robinson
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The Walker circulation connects the regions with deep atmospheric convection in the western tropical Pacific to the shallow-convection, tropospheric subsidence, and stratocumulus cloud decks of the eastern Pacific. Although important to many elements of the Earth system such as tropical precipitation, and cloud feedback processes, interactions between large-scale tropical circulations and these cloud systems are still not well understood. The purpose of this study is to better understand the multi-scale interactions between the Walker circulation, cloud systems, and interactive radiation.
To do this we simulate a mock-Walker Circulation with a full-physics General Circulation Model (GCM) using idealized boundary conditions. Our experiments use a doubly-periodic domain with grid-spacing of 1, 2, 25, and 100km. We thus span the range from General Circulation Models (GCMs) to Cloud-system Resolving Models (CRMs). Our model is derived from the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric GCM (AM4.0). Our GCM-like experiments have a large low-level cloud fraction while the CRM-like experiments have more upper-level clouds. This difference leads to opposite atmospheric responses to changes in the longwave cloud radiative effect (LWCRE). Active LWCRE lead to increased precipitation for our GCMs, but decreased precipitation for our CRMs. The LWCRE leads to a narrower rising branch of the circulation and substantially increases the fraction of precipitation from the large-scale cloud parameterization. Decreasing the grid-spacing to 1km and 2km results in stronger overturning circulations, more condensate aloft, and less precipitation. This work demonstrates that a mock-Walker circulation is a useful generalization of RCE that includes a large-scale circulation.
Feb 2021Published in Journal of Advances in Modeling Earth Systems volume 13 issue 2. 10.1029/2020MS002196