SCREAM is a full featured atmospheric global circulation model with a
nonhydrostatic dynamical core and state-of-the-art parameterizations
for microphysics, moist turbulence and radiation. It has been written
from scratch in C++ with the Kokkos library used to abstract the
on-node execution model for both CPUs and GPUs.  SCREAM contains
several algorithmic innovations including a highly efficient
HEVI-IMEX timestepping and semi-Lagrangian tracer transport and
separate physics/dynamics grids which exploits the effective resolution
of the dynamics.  

In this presentation we will show SCREAM's Exascale performance on the
DOE OLCF Frontier system, as well as SCREAM's performance portability
across a wide range of CPUS and multiple GPUs from AMD and NVIDIA.
On Frontier, SCREAM obtains record setting performance.  At global
cloud permitting resolution (3.25 km grid spacing ) it runs well on
27,000 AMD MI250 GPUs, obtaining a throughput of 1.26
simulated-years-per-day.