1. ALADIN view of the way forward J.-F. Geleyn, ALADIN PM (also for F. Bouttier, C. Fischer and M. Janoušek) EUMETNET SRNWP Interoperability Workshop, Reading, 14-15/1/2008

2. Foreword n What follows is a draft set of proposals, for steering discussion n It is based on the experience of the ALADIN community, in its links with Météo-France (‘provider’ for the coupling on the ARPEGE side, i.e. with a complex global horizontal geometry) n It is aimed at addressing as globally as feasible the deliverables D1/D3/D4/D5+D6.

3. Basic principles n Software developed for deliverable D4 (‘post- processing’) should be reusable as much as feasible for deliverables D5/D6 (‘coupling’). n Double interpolation should be avoided when it does not endanger the spirit of the common effort (e.g. in the horizontal). n One should clearly separate two issues: –Vertical structure (and variable content), orography, surface characteristics and variables; –Horizontal geometry. n The common standardisation effort should be clearly concentrated on the first issue, the second one better remaining ‘bilateral’.

4. Ensuing proposal items (1/3) n Single exchange file format. n Horizontal geometry of exchanged files left to the responsibility of the producer (either original, or interpolated [with care for orographic issues] on a bilateral agreement basis). n Horizontal interpolation issues for final production (post-processed product as well as coupling files) of the responsibility of the user (better tailored to local specific needs). n Data interpolation/conversion in the vertical under the responsibility of the producer.

5. Ensuing proposal items (2/3) n For the ‘vertical’ content of the exchange files (including surface aspects), two solution are possible: –Like for the horizontal (i.e. original and/or bilaterally agreed); –A common intermediate standard (recommended). n The choice for the orography is similar but may be decoupled from the previous one: –What is the definition of a ‘common’ orography? –Possibility of having differing orographies between upper-air and surface computations in some Consortia.

6. Ensuing proposal items (3/3) n Generation of commonly agreed post- processed parameters (e.g. PV, fields on special levels, …) under the responsibility of the producer (otherwise, it is often too late). n Special attention to be dedicated to the (much model dependent) parameters (and characteristics) of the surface. n The same may apply to cloud and precipitation properties, if exchanged (at least for post-processing).

7. Items to be checked n Support of the common exchange file format for all horizontal geometries. Staggering issue. n Idem for the ‘vertical’ structure(s), staggering issue included. n Decision needed about the single or multiple choice for the ‘vertical’. n Idem for the orographic item. n Creation of a commonly agreed list of variables/parameters. Metadata system for maintenance and documentation. n For the surface avoid both being ‘simplistic’ and ‘model-specific’. n Separate ‘local’ & ‘common’ development needs.

8. Outlook n Discussion needed on all raised aspects during the workshop. n It might be interesting to re-read the items lists after common conclusions have been reached (as a safeguard against forgotten hurdles or issues).