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Abstract

SpeedyWeather.jl is a library to simulate and analyze the global atmospheric circulation on the
sphere. It implements several 2D and 3D models which solve different sets of equations:
• the primitive equations with and without humidity (Figure 1),
• the shallow water equations (Figure 2), and
• the barotropic vorticity equation (Figure 3).
The primitive equation model in SpeedyWeather.jl is an atmospheric general circulation model
(Kucharski et al., 2013) with simple parameterizations for unresolved physical processes including
precipitation or boundary layer mixing. It can be thought of as a conceptual reinvention of the
Fortran SPEEDY model (Molteni, 2003) in the Julia programming language (Bezanson et al.,
2017). However, all models here are written in a modular way to make its components easily
extensible. For example, a new parameterization can be externally defined and passed as an
argument to the model constructor. Operators used inside SpeedyWeather.jl are exposed to
the user, facilitating analysis of the simulation data. SpeedyWeather.jl is therefore, beyond its
main purpose of simulating atmospheric motion, also a library for the analysis of gridded data
on the sphere. Running and analyzing simulations can be interactively combined, enhancing
user experience and productivity.