Abstract. A coupler is a fundamental software tool for Earth system modeling. Targeting the requirements of 3-D coupling, high-level sharing, common model software platform and better parallel performance, we started to design and develop a community coupler (C-Coupler) from 2010 in China, and finished the first version (C-Coupler1) recently. C-Coupler1 is a parallel 3-D coupler that achieves the same (bitwise-identical) results with any number of processes. Guided by the general design of C-Coupler, C-Coupler1 enables various component models and various coupled models to be integrated on the same common model software platform to achieve a higher-level sharing, where the component models and the coupler can keep the same code version in various model configurations for simulation. Moreover, it provides the C-Coupler platform, a uniform runtime environment for operating various kinds of model simulations in the same manner. C-Coupler1 is ready for Earth system modeling, and it is publicly available. In China, there are more and more modeling groups using C-Coupler1 for the development and application of models.

Abstract. Reliable numerical simulation plays a critical role in climate change study. The reliability includes bitwise identical reproducibility, i.e. bitwise identical result of numerical simulation can be reproduced. It is important to Earth system modeling and has already been used intra modeling groups for the model development. However, it is rarely considered in a wider range even worldwide. To help achieve the worldwide bitwise identical reproducibility, we introduce the detailed implementations for the bitwise identical reproducibility on the Community Coupler (C-Coupler) platform, a uniform runtime software environment that configures, builds and runs the models in the same manner. Moreover, we share a series of experiences and suggestions regarding the bitwise identical reproducibility. We believe that these implementations, experiences and suggestions can be easily extended to other model software platforms and can prospectively advance the model development and scientific researches in the future.

Abstract. Reproducibility is a fundamental principle of scientific research. Bitwise identical reproducibility, i.e., bitwise computational results can be reproduced, guarantees the reproduction of exactly the same results. Here we show the importance of bitwise identical reproducibility to Earth system modeling but the importance has not yet been widely recognized. Modeled mean climate states, variability and trends at different scales may be significantly changed or even lead to opposing results due to a slight change in the original simulation setting during a reproduction. Out of the large body of Earth system modeling publications, few thoroughly describe the whole original simulation setting. As a result, the reproduction of a particular simulation experiment by fellow scientists heavily depends on the interaction with the original authors, which is often inconvenient or even impossible. We anticipate bitwise identical reproducibility to be promoted as a worldwide standard, to guarantee the independent reproduction of simulation results and to further improve model development and scientific research.

Reproducibility and reliability are fundamental principles of scientific research. A compiling setup that includes a specific compiler version and compiler flags is an essential technical support for Earth system modeling. With the fast development of computer software and hardware, a compiling setup has to be updated frequently, which challenges the reproducibility and reliability of Earth system modeling. The existing results of a simulation using an original compiling setup may be irreproducible by a newer compiling setup because trivial round-off errors introduced by the change in compiling setup can potentially trigger significant changes in simulation results. Regarding the reliability, a compiler with millions of lines of code may have bugs that are easily overlooked due to the uncertainties or unknowns in Earth system modeling. To address these challenges, this study shows that different compiling setups can achieve exactly the same (bitwise identical) results in Earth system modeling, and a set of bitwise identical compiling setups of a model can be used across different compiler versions and different compiler flags. As a result, the original results can be more easily reproduced; for example, the original results with an older compiler version can be reproduced exactly with a newer compiler version. Moreover, this study shows that new test cases can be generated based on the differences of bitwise identical compiling setups between different models, which can help detect software bugs in the codes of models and compilers and finally improve the reliability of Earth system modeling.Published by Copernicus Publications on behalf of the European Geosciences Union.

Abstract. Reliable numerical simulation plays a critical role in climate change study. The reliability includes the technical reproducibility, i.e. bit-identical results of numerical simulation can be reproduced. It is very important for model development and scientific researches but has not been satisfactorily addressed yet so far. To address the technical reproducibility, necessary information about it is firstly analyzed, and how to enhance it on the Community Coupler (C-Coupler) platform, a uniform runtime environment that can operate various kinds of model simulations in the same manner, is then detailed. Moreover, we share a series of experiences and suggestions with scientists and model groups for achieving the technical reproducibility. We believe that, the proposed implementations, experiences and suggestions can be easily extended to other model platforms, and can prospectively advance model development and scientific researches in future.