Global Cloud Resolving Atmospheric Modeling on Exascale Computers

EAMxx is the new global atmosphere model for E3SM designed to leverage the cutting edge in exascale computing. This seminar will discuss the design structure of the new EAMxx code base and present results of the Simple Cloud Resolving E3SM Atmosphere Model (SCREAM) configuration which has a target resolution of 3km horizontal grid spacing.  Obtaining reasonable simulation speed at this resolution requires use of graphical processing units (GPUs).  EAMxx is written in C++ using the Kokkos library to achieve performance on GPUs and on conventional computer architectures.  By keeping the EAMxx code base simple, implementation of SCREAM version 1 was achieved by a relatively small team in less than 4 years.  Minimizing complexity also has the benefit of making results easier to understand and therefore trust.  Another pillar of the SCREAM project is exhaustive unit testing, which has helped avoid bugs.  In this presentation, we will provide lessons learned from EAMxx development and analysis of existing EAMxx simulations, which shows that increased resolution fixes many but not all biases in the standard E3SM model.  We will also present the latest performance results from a simulation campaign on Frontier using GPUs. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, LLNL-ABS-856762