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Cloud Process Coupling and Time Integration in the E3SM Atmosphere Model
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  • Sean Patrick Santos,
  • Christopher Bretherton,
  • Peter Caldwell,
  • Sean Patrick Santos
Sean Patrick Santos
University of Washington

Corresponding Author:spsantos@uw.edu

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Christopher Bretherton
University of Washington, University of Washington
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Peter Caldwell
Lawrence Livermore National Laboratory, Lawrence Livermore National Laboratory
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Sean Patrick Santos
Columbia University

Corresponding Author:sean.p.santos@columbia.edu

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In this study, we find significant sensitivity to the choice of time step for the Energy Exascale Earth System Model's atmospheric component, leading to large decreases in the magnitude of cloud forcing when the time step is reduced to 10 seconds. Reducing the time step size for the microphysics increases precipitation, leading to a drying of the atmosphere and an increase in surface evaporation. This effect is amplified when the microphysics is substepped together with other cloud physics processes. Coupling the model's dynamics and physics more frequently reduces cloud fraction at lower altitudes, while producing more cloud liquid at higher altitudes. Reducing the deep convection time step also reduces low cloud mass and cloud fraction. Together, these results suggest that cloud physics in a global circulation model can depend strongly on time step, and in particular on the frequency with which cloud-related processes are coupled with each other and with the model dynamics.
May 2021Published in Journal of Advances in Modeling Earth Systems volume 13 issue 5. 10.1029/2020MS002359