What is MESSy?

The Modular Earth Submodel System (MESSy) is a software and a framework for the assembly of Earth System Models (ESMs). MESSy is a multi-institutional project.

The MESSy software provides a modular kit with generalized interfaces for the standardized control and coupling of low-level ESM components. These components describe individual processes in the troposphere and middle atmosphere and also feedback with ocean, land and anthropogenic influences. They are called submodels in MESSy and comprise currently about 110 submodels. MESSy provides the full hierarchy of model systems ranging from idealised box model setups, over simplified climate model configurations, global circulations models including atmospheric chemistry, to fully coupled representations of the Earth system including coupling with an interactive ocean.

MESSy structure. Image: DLR, CC BY-NC-ND 3.0

The most used model configuration is the ECHAM/MESSy Atmospheric Chemistry (EMAC) model, which is a numerical chemistry and climate simulation system. The underlying atmosphere model, more specificly the spectral dynamical core, the large-scale advection, and the „nudging“-method are originally from ECHAM (the 5. generation of “European Centre HAMburg general circulation model” Roeckner et al., 2006). However, all physical parameterisations from ECHAM have been in the meantime replaced by respective further developed MESSy submodels and also new submodels were added.

Therefore, when using EMAC, it is clear, that one uses the spectral dynamical core of ECHAM, but one needs to select explicitly the submodels for cloud or radiation or other processes. Alternatively, the dynamical core of the CESM1 model can be selected or, as latest addition, ICON, which provides a grid-point dynamical core. Beyond that, MESSy also allows regional zooming via n nested instances of the COSMO model in a MECO(n) setup. MECO(n) is short for MESSy-fied ECHAM and COSMO models nested n times.

Illustration of the complexity range covered by MESSy models. In the projection plane, the range of chemical and physical complexity available is depicted at the example of EMAC. The physical complexity (horizontal axis) ranges from 0D box models, over prescribed dynamics, quasi chemical transport model (QCTM) mode to fully prognostic chemistry climate models or even ESMs, if other compartment models are added as well. The chemical complexity (vertical axis) ranges from prescribed mixing ratios of important (w.r.t. radiation) gases, over simplified methane chemistry, pure stratospheric chemistry to comprehensive atmospheric chemistry including organics in gas and liquid phase. The third axis, which points out of the projection area, shows that in addition to the global EMAC model, MECO(n) also allows dynamic downscaling of atmospheric chemistry applications to a resolution of a few kilometres. Image: DLR, CC BY-NC-ND 3.0

Overall MESSy provides a flexibility in scientific application, because the users configure the model with respect to their scientific focus. The MESSy approach offers several benefits: A scalable model development and several different implementations of processes and diagnostics can coexist in the same model code. Nonetheless, the overall complexity remains controllable in a transparent and user friendly way. A high flexibility is achieved through the modularity, providing a research tool for a large community serving a wide variety of scientific needs. The development of MESSy and its submodels is a multi-institutional effort. Scientific and technical exchange between the different groups and institutions is coordinated by the MESSy community.

MESSy submodels cover a large variety of applications and can be grouped into infrastructure submodels (framework), diagnostic submodels, model physics submodels, and atmospheric chemistry submodels including kinetics, photolysis, emissions, aerosols, and sinks. Further information on the individual submodels are available here. The process and diagnostic submodels are connected via a standard interface to  the MESSy infrastructure. The infrastructure covers several submodels dealing with rather technical details, as memory or object management, or input/output.

The main design concept of MESSy is the strict separation of these process and diagnostic submodels from model HPC software infrastructure like memory management, input/output, flow control and so on. This is referred to as ‘separation of concerns’ and operator splitting is used as the fundamental concept. The model codes is organized in four conceptual software layers as a basis for internal modularity. Object-oriented approaches are utilized where possible, taking into account the computational performance.

To summarize, the MESSy approach provides a research tool for a large community serving a wide variety of scientific needs. Yet, the overall complexity remains controllable in a transparent and user-friendly way. Clearly, MESSy is and has proven to be a long-term solution for the modelling community, since it is able to adapt to changes and changing community requirements with its modular structure. An overview of current MESSy setups is shown in the right figure. Applications of the MESSy system range from idealized 0-D simulations to fully coupled representations of the Earth system. The level of detail in atmospheric processes can be selected by users according to their scientific needs.

The concepts of MESSy are summarized on this poster (pdf).