28/02/2018
ECMWF: Scientist / Senior Scientist to work on dynamical core aspects related to the 4D-VAR Data Assimilation System

ECMWF, Shinfield Park, Reading, UK

Summary of the role
An accurate forecast model and accurate initial conditions are essential for producing medium range forecasts. The forecast model together with the 4D-VAR data assimilation system are the two key and intimately interconnected components of the ECMWF Integrated Forecast System (IFS). The role of the 4D-VAR system is to compute the initial state of the atmosphere by minimizing a space-time depended objective cost function measuring the distance of the initial model state from observations. Solving this computationally expensive problem, requires repeated forward-backward integrations of the tangent-linear (TL) and the adjoint (AD) version of the nonlinear model. Accurate, robust and efficient TL/AD models are essential for producing high quality analyses within the tight time constraints the operational model must satisfy.

The numerical algorithms of the spectral transform, semi-implicit, semi-Lagrangian IFS dynamical core are continuously improved to increase its predictive skill, efficiency and scalability as resolution increases and High Performance Computing (HPC) architectures shift towards exascale designs. It is essential that TL/AD models remain competitive and compatible with the changes of the non-linear forecast model. This is a task that requires significant effort and an ability to often compromise competing development needs in terms of accuracy and stability between the nonlinear and tangent-linear model.

This position sits in the Numerical Methods Team of the Earth System Modelling (ESM) Section of the Research Department. The successful candidate will contribute to TL/AD model developments linked with both the current and future dynamical core options. He or she will be the first point of contact for troubleshooting TL/AD issues collaborating with colleagues in the Physical Processes Team of the Earth System Modelling Section. He or she will be expected to participate in the research and development activities of the Numerical Methods Team related to the maintenance and further improvement of the semi-implicit, semi-Lagrangian formulation of the hydrostatic and non-hydrostatic dynamical core options of the IFS.

An important activity in the Numerical Methods Team is the development of an alternative non-hydrostatic, Finite-Volume dynamical core and other work assigned to this role will be to develop a TL/AD counterpart for the new dynamical core option.

Ideally, the successful candidate will have very good knowledge of numerical methods for global atmospheric models as well as strong expertise in tangent-linear and adjoint methods used in variational data assimilation or parameter estimation. Familiarity and experience in semi-implicit, semi-Lagrangian modelling will be an advantage.

This position involves significant interaction with all the other teams within the Earth System Modelling Section as well as across other sections. Therefore, the successful candidate must have the ability and willingness to communicate effectively with other scientists as well the ability to organise and plan the scope of the work on TL/AD developments appropriately.

Main duties and key responsibilities

  • Developing TL/AD models for the current and future IFS dynamical core and maintaining/testing these models between IFS software cycles
  • Developing/maintaining diagnostic tools for validating TL/AD developments
  • Developing a TL/AD model framework for adjoint sensitivities and for use in parameter optimization
  • Acting as the first point of contact in the Earth System Modelling Section for operational issues related with TL/AD models
  • Participate in numerical algorithm developments for the IFS dynamical core such as improvement of the semi-Lagrangian, semi-implicit hydrostatic and non-hydrostatic formulations

Grade remuneration

This position is graded A2/A3 in line with the scales of the Co‑ordinated Organisations.
For the A2 grade, the minimum annual basic salary will be £58,238.40 net of tax.
For the A3 grade, the minimum annual basic salary will be £71,861.52 net of tax.
Recruitment at the higher grade may be considered where the level of the candidate’s skills and experience exceeds the requirements of the position. This will be at the discretion of the organisation. This position is assigned to the employment category STF-C as defined in the Staff Regulations.

Full details of salary scales and allowances are available on the ECMWF website at www.ecmwf.int/en/about/jobs, including the Centre’s Staff Regulations regarding the terms and conditions of employment.

Starting date: As soon as possible.

Length of contract: Four years, with the possibility of a further contract.