The MESSy DWARF (based on MESSy v2.55.2)

Abstract. The adaptation of Earth system model (ESM) codes to modern computing architectures is challenging as ESMs consist of a multitude of different components. Historically grown and developed by scientists rather than software engineers, the codes of the individual components are often interwoven, making the optimisation of the ESMs rather challenging, if not impossible. Thus, in the last few years, the codes have become increasingly modularised, and, with that, different components are now disentangled from each other. This helps porting the code section by section to modern computing architectures, e.g. to GPUs. For more than 20 years, the modularisation has been the fundamental concept of the Modular Earth Submodel System (MESSy). It is an integrated framework providing data structures and methods to build comprehensive ESMs from individual components. Each component, e.g. a cloud microphysical scheme, dry deposition of tracer gases, or diagnostic tools, as output along satellite orbits, is coded as an individual so-called submodel. Each submodel is connected via the MESSy infrastructure with all other components, together forming a comprehensive model system. MESSy was mainly developed for research in atmospheric chemistry, and, so far, it has always been connected to a dynamical (climate or weather forecast) model, i.e. what we call a base model. The base model is a development outside the MESSy framework. Running a full dynamical model for technical tests when porting only one submodel is a tedious task and unnecessarily resource-consuming. Therefore, we developed the so-called MESSy DWARF, a simplified base model based on the MESSy infrastructure. We implemented the definition of a very simple grid, a parallelisation scheme, and a time control to replace a fully fledged base model. The MESSy DWARF serves as a valuable tool for technical applications, such as porting individual component implementations to GPUs and performance tests or as an easy test environment for process implementations. Due to the MESSy structure, the applied components can be used in a dynamical model without any changes because the interface is exactly the same. Furthermore, the MESSy DWARF is suited for scientific purposes running simplified models (with only a selection of components), e.g. a chemical box model for the analysis of chamber experiments or a trajectory box model imitating an air parcel rising slowly into the stratosphere. Column and plume models could also easily be built based on the DWARF. In this article, we introduce the technical setup of the MESSy DWARF and show four example applications: (1) a simple application using a component calculating orbital parameters, (2) a chemical kinetics model including photolysis frequency calculation, (3) an application of a chemical box model, and (4) some details on a GPU performance test of the chemical kinetics model.