Abstract
Clouds, especially low clouds, are crucial for regulating Earth’s energy
balance and mediating the response of the climate system to changes in
greenhouse gas concentrations. Despite their importance for climate,
they remain relatively poorly understood and are inaccurately
represented in climate models. A principal reason is that the high
computational expense of simulating them with large-eddy simulations
(LES) has inhibited broad and systematic numerical experimentation and
the generation of large datasets for training parametrization schemes
for climate models. Here we demonstrate LES of low clouds on Tensor
Processing Units (TPUs), application-specific integrated circuits that
were originally developed for machine learning applications. We show
that TPUs in conjunction with tailored software implementations can be
used to simulate computationally challenging stratocumulus clouds in
conditions observed during the Dynamics and Chemistry of Marine
Stratocumulus (DYCOMS) field study. The TPU-based LES code successfully
reproduces clouds during DYCOMS and opens up the large computational
resources available on TPUs to cloud simulations. The code enables
unprecedented weak and strong scaling of LES, making it possible, for
example, to simulate stratocumulus with $10\times$
speedup over real-time evolution in domains with a $34.7
\mathrm{km} \times 53.8
\mathrm{km}$ horizontal cross section. The results
open up new avenues for computational experiments and for substantially
enlarging the sample of LES available to train parameterizations of low
clouds.