Paris, le 17 Mars 2005
As per distribution list
Dear Colleagues,
I realise from informal exchanges between ALADIN scientists and from conversations with some of you, that you may not have, through “bottom-up” loops, full information on the outcome of ALADIN-2 work performed by Météo-France, since we last met in Split. This obviously requires corrective action on my side, and the purpose of this letter is to update you.
The steps taken by Météo-France were required due to a number of facts that occurred, or could only be fully appreciated after the Split meeting, following in-depth analysis and investigations. As you will see hereafter, they were all taken in the Split spirit, in line with a common ALADIN-2 strategy involving all Partners in the ALADIN, ALARO and AROME sub-projects and in the cooperation with HIRLAM.
In December, we first found out that the precipitation data used in the comparison experiments of this summer, were not the full precipitation output of the ‘ALARO-10’ prototype model. However, the re-analysis of the correct results confirmed that the basic conclusions of our Split meeting remained valid, even if with slightly different consequences: despite higher computer cost, the ‘ALARO-10’ prototype does not produce better precipitation outputs than ALADIN, the micro-physics scheme is very sensitive to increasing time step and specific efforts are required on convection at intermediate scale.
Based on this finding, we continued to analyse in more depth how to optimise the implementation of the strategy and technical approach that we had sketched together in Split, and to define in detail our own contribution.
This analysis revealed that:
We had underestimated the technical obstacles to the development of the “clean” physical/dynamical interfacing required to unify all models from ARPEGE to AROME and to fulfil HIRLAM cooperation requirements;
Substantial additional work is required to make the so-called ‘externalised surface’ more operational and flexible and to create boundary conditions compatible with all model configurations to be used across the Partners;
An ALADIN-2 partnership compatible with our respective research and operational objectives and capabilities, requires a unified strategy involving ARPEGE, ALADIN, ALARO and AROME.
The second point had actually been missed and was not discussed at all in Split, and was highlighted at a follow-up workshop, as a blocking issue, and Météo-France decided accordingly to assign high priority and to dedicate additional resources to this issue. This is a “must” because it relates to the “ALADIN phasing”, one of our basic strengths.
In line with the commitment I made in Split, we also discussed how to best create the practical conditions for involving ALADIN scientists across the three ALADIN, ALARO and AROME sub-projects.
Overall, this resulted, after a rather long consolidation work, in an important aggiornamento and revised proposal, which I can summarise as follows:
The implementation of our common strategy has to consider ARPEGE-ALADIN-ALARO-AROME as a continuous entity, unified by a flexible and operational ‘externalised surface’ and boundary conditions, enabling the continuation of our “phasing” approach across all model configurations;
In order to give equal weight to the ‘reconvergence’ and ‘tool-box’ pillars of our ALADIN-2 partnership, ALARO has to be considered as a framework – not a model - enabling in the future each Partner to configure its LAM, based on its own choice of physics options, from ARPEGE to AROME/Meso-NH options, with possible intermediate choices;
We have to base the definition of our joint work plans on ‘work-streams’ across the ALADIN, ALARO and AROME sub-projects (e.g. ‘interfacing’, ‘surface externalisation’, ‘Meso-NH physics testing’, etc.), each work stream having its own schedule and work-sharing practices;
Thus:
The current ALARO-targeted work will directly contribute to AROME (especially on interfacing aspects), whilst helping all ALADIN (and HIRLAM) Partners to get progressively acquainted with AROME characteristics;
Duplication of work will be avoided between the upgrade of the ARPEGE physics and some ALARO transitional aspects, which will minimise the extra effort needed to prepare for a first good ALARO version in 2006;
The participation of the Partners in the AROME development will not be limited to the above-mentioned ALARO-targeted work, but will encompass scientific and technical issues under the work-streams;
Considering the extra work required in the short term on the ‘externalised surface’, we have to relax the too tight intermediate 2005 ALARO schedule, whilst keeping the same target of end 2006 for a marked evolution with respect to ALADIN based on AROME-type ingredients;
The common objective for 2006 should be to achieve the first phasing compatible with all model configurations, enabling each Partner to use for research and/or operations any configuration of the ALARO framework, based on suitable boundary conditions;
In addition, also in 2006, we will offer a portable version of the AROME software to Partners, together with installation support and training, to facilitate our preparation for AROME and the participation of ALADIN scientists in testing and evaluation of preoperational versions.
I am aware that some of the above could have been formulated earlier and appropriated by all of us, if the schedule and work load had not been so demanding in the second half of 2004. We certainly accept our share of responsibility in this, but I can assure you that we have made all possible efforts to define what we believe is the most promising and balanced implementation of our common strategy in the short, medium and long term.
Making this perspective a reality deserves and requires full support and commitments of all of us and of our scientists, who have now access to a lot of documents outlining the implications of the above. As I am told that some of them are already convinced of the advantage of familiarising themselves with AROME in the spirit of a continuous evolution of ALADIN, I trust that the indispensable consensus will develop further, and that you will confirm your commitment on that basis.
On our side, I can assure you that we remain more than ever committed to our ALADIN-2 Partnership, and have accordingly dedicated additional resources to ALARO-targeted work and to making our AROME prototype software more portable and user friendly, along the lines described above.
With my best personal regards,
Alain Ratier
Deputy Director-general
