Missions

The general mission is to merge the OASIS3-MCT code coupler and the XIOS I/O server, respectively developed by Cerfacs and LSCE/CEA. OASIS3-MCT and XIOS are two tools widely used in the French climate modelling community. OASIS3-MCT exchanges data between the numerical codes modelling the various components of the earth system (atmosphere, ocean, sea ice, etc.), enabling them to interact with each other, while XIOS writes the data generated by these models to disk. The two tools have a number of similar functions, such as data communication (between two codes or from one code to the disk) and data transformation, for example to remesh data between the grids of the two codes to be coupled or from the grid of one code to another lower-resolution grid used to store the results on disk. The aim is therefore to merge these two tools, in order to bring together the functionalities and concentrate development efforts within one single tool. The aim of the assignment is therefore to complete the analysis of the two tools, define a development strategy and merge them into a single tool combining the functions of a code coupler and an I/O server. In practice, as the latest version of the XIOS3 I/O server includes code coupling functions thanks to its new design, the merger is envisaged by upgrading XIOS to ensure that all the functions present in OASIS3-MCT are also present in XIOS.

Activités

- Get familiar with the current tools, OASIS3-MCT and XIOS.

- Analyse the functionalities offered by each of the tools and draw up a list of developments to be made in XIOS to include at least all the coupling functionalities of OASIS3-MCT.

- Carry out test cases, each activating one OASIS3-MCT function and reproducing it with XIOS if possible; note the limitations or advantages of XIOS compared with OASIS3-MCT for each case.

- Produce a complete toy coupled model of a community earth system model (ESM), firstly with OASIS3-MCT and then with XIOS. A toy coupled model reproduces the coupling exchanges of a real coupled model (in terms of coupling algorithm, number and size of fields to be exchanged, interpolations to be activated to express the fields produced by a source component on the grid of the target component) but without including the complexity of the science modelled by the component. It will enable to identify the differences in terms of code interfacing and configuration between OASIS3-MCT and XIOS.

- Propose and implement developments in XIOS to resolve any difficulties or impossibilities encountered in assembling the coupled toy model.
-Study the performance and scalability of the various coupling stages with XIOS (initialisation, calculation of remeshing matrices, coupling exchanges as such, termination) as well as their portability to different computing platforms at CERFACS, in France (GENCI resources) and in Europe (EuroHPC resources).
-Propose and implement developments in XIOS to resolve any difficulties or impossibilities encountered in assembling the coupled toy model. -To study the performance and scalability of the various coupling stages with XIOS (initialisation, calculation of remeshing matrices, coupling exchanges as such, termination) as well as their portability to different computing platforms at CERFACS, in France (GENCI resources) and in Europe (EuroHPC resources).

- Assemble a real coupled model of our community's earth system with the advanced version of XIOS to replace the historical OASIS3-MCT coupler.

- Produce technical and functional documentation for the XIOS coupling functionality and its API (Application Programming Interface)

In parallel with the above activities, the engineer could organise and/or take part in in-person and online training sessions on the coupling functionality of the advanced version of XIOS. He/she may also present this tool at symposia and conferences and participate in the writing of publications in peer-reviewed journals.

Compétences

Technical skills
- Master's degree in HPC scientific computing or equivalent
- Development of parallel numerical codes
- Programming in Fortran, C and C++
- Drafting technical documentation.
- Knowledge of English required for understanding and writing technical documentation and for international exchanges (level C1 - European reference framework)

Personal skills
- Ability to work in a team
- Ability to interact with users of a community code.

Contexte de travail

This position is part of the COMPACT project, one of the PEPR TRACCS Targeted Projects funded by the French National Research Agency over the period 2024-2032. The engineer will work in the CERFACS climate modelling and global change team, which includes around forty researchers, engineers, PhD students and post-docs. The engineer will interact mainly with the team developing the OASIS3-MCT coupler (3 or 4 people) and with the XIOS developers at LSCE/CEA (2 people). Although based in Toulouse, he/she may be required to travel to LSCE/CEA in Paris/Saclay and elsewhere in France to take part in COMPACT project meetings. Development will be carried out on CERFACS computing machines, but the software will have to be tested on different platforms in France (Météo-France computer and GENCI resources) and in Europe (EuroHPC resources).

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

NTR