Around once per month we hold an informal 1-hour online meeting mainly involving developers at European forecasting centres who use ecRad, to discuss technical developments to ecRad. Regular attendees are:
- Robin Hogan, Balthasar Reuter, Johan Ericsson & Ahmad Nawab (ECMWF)
- Daniel Hupp (MeteoSwiss)
- Mareike Burba & Daniel Rieger (DWD)
- Sophia Schaefer, Philippe Marguinaud & Erwan Cossevin (Meteo-France)
- Kristian Pagh Nielsen, Ole Lindberg (DMI)
- Jean-Francois Grailet (U. Liege)
If you are actively working on ecRad and would like to participate, please contact Robin Hogan. These meetings have been held since 2021 but minutes have only been recorded since October 2025.
Meeting on 9 March 2026
Johan provided an update on his work on the Loki GPU version, focussing on using the ecCKD gas optics scheme with the Tripleclouds solver. Loki generates OpenACC annotated Fortran and the target architecture is ECMWF NVIDIA A100 GPUs. This involves some changes to the core ecRad code such as changing "allocatable" to "pointer", which is a current PR. Things like hoisting variables up a level are required but can be done automatically by Loki so wouldn't need a change to ecRad. There are a few more things coming down the line, such as replacing "transpose" with inline code that works on GPUs and making some array dimensions explicit. The PR for this is in progress. Johan demonstrated the new wrapper layer for the IFS to interface FIELD_API with ecRad. Since this is IFS-specific it will likely not be in the "radiation" library built by ecRad, but could be included in the ifs directory of the ecRad repository for information. The only remaining issue is lack of bit-reproducibility for parallel runs, but when this bug is found the next step will be to compare the performance and accuracy with the CPU version. Note that the MeteoSwiss/ICON GPU version of ecRad chose to do the GPU version of a different configuration of ecRad: the RRTMG gas optics together with the McICA solver, so direct comparison with the ECMWF version is not really possible.
Meeting on 3 November 2025
We briefly discussed Johan's work to replace allocatable with pointers: this had caused some issues at DWD with the NEC compiler but they have since been resolved.
Marieke's work during her secondment at ECMWF this autumn was discussed: she has added an additional output diagnostic to ecRad containing the "true" direct beam radiation, without including forward scattering that is inherent in using delta-Eddington scaling. This leads to better agreement when comparing Direct Normal Irradiance (DNI) with BSRN pyrheliometer observations. Kristian pointed out the https://solarstations.org/ web site containing a wider range of sites for validating DNI forecasts than BSRN and a best practices handbook for using solar resource data for solar energy applications. He wondered whether the delta-Eddington DNI might be better for PV forecasting given they accept radiation from a wider range of angles than a pyrheliometer, although agreed that for concentrated solar power as used, for example, in Spain, the "true" DNI should be more relevant. He also pointed out the various instruments that can be used from Kipp & Zonen, Delta-T and Hukseflux. The suggestion was raised to also look at the impact of the two definitions of DNI on forecasted sunshine duration, although accepting that this is an imperfect diagnostic.
Sophia briefly summarised some sensitivity studies she is doing with AROME over France & Central Europe, finding that there are lots of compensating errors but that lowering "FSD", the in-cloud fractional standard deviation of water content, helps reduce RMSE.
Meeting on 2 October 2025
Balthasar summarised the ongoing work of Paul Mullowney, who working on a new ecRad branch "master-omp" (https://github.com/ecmwf-ifs/ecrad/tree/master-omp) that consists of an OpenMP port targeting AMD GPU platforms with the Nvidia compiler and the AMD offloading compiler. Part of the challenge is because of a limitation of the Fortran compiler in supporting type-bound procedures, necessitating replacing these with stand-alone procedures. Daniel Rieger reports that this aspect of ecRad can be a showstopper on some hardware so this branch might be useful more widely.
Robin briefly mentioned his ongoing work with Emma Turner to extend the ecCKD gas optics into the far UV (115-200 nm) rather than stopping at 200 nm, particularly to enable CAMS photolysis calculations to use ecRad rather than their own radiative transfer scheme.
Robin also suggested that a similar approach that Balthasar had implemented in ecRad of treating it as an external library in the IFS could be applied to RTTOV. A conversation has been initiated on this with RTTOV developers at ECMWF.
Johan presented some slides summarising his work to replace allocatable arrays in ecRad with pointers, enabling memory allocation within GPU kernels to be avoided: on a GPU this memory would be externally managed, while on CPUs the change is simply to allocate memory to pointers rather than "allocatable" arrays. He reported that on CPUs this even leads to a 10-15% speed-up in normal operation on intel compiler although around neutral with gFortran.