Stable Simulation of the Community Atmosphere Model Using
Machine-Learning Physical Parameterization Trained with Experience
Replay
Abstract
In recent years, machine learning (ML) models have been used for
improving physical parameterizations of general circulation models
(GCMs). A significant challenge of integrating ML models into GCMs is
the online instability when they are coupled for long-term simulation.
In this study, we present a new strategy that demonstrates robust online
stability when the entire physical parameterization package of a GCM is
replaced by a deep ML algorithm. The method uses a multistep training
scheme of the machine learning model with experience replay in which the
memory of physical tendencies from the training dataset and the ML
algorithm’s own output at the previous time step are used in the
training. The physics memory improves the accuracy of the machine
learning model, while the experience replay constrains the amplification
of cumulative errors in the online coupling. The method is used to train
the whole physical parameterization package for the Community Atmosphere
Model version 5 (CAM5) with data from its Multi-scale Modeling Framework
(MMF) high resolution simulations. Three 6-year online simulations of
the CAM5 with the ML physics package at operational spatial resolution
with real-world geography are presented. The simulated spatial
distributions of precipitation, surface temperature and zonally averaged
atmospheric fields demonstrate overall better accuracy than that of the
standard CAM5 and benchmark model even without the use of additional
physical constraints or tuning. This work is the first to demonstrate a
solution to address the online instability problem in climate modeling
with ML physics by using experience replay.