1. Presently performed by SWECLIM (the Swedish regional climate modelling programme) that involves the Rossby Centre of the SMHI and two Swedish universities SWECLIM terminates in June 2003. The Rossby Centre activity continues. Activities also at Swedish universities. Climate modeling in Sweden Climate modeling in Sweden Markku Rummukainen, SMHI/Rossby Centre and SWECLIM Erland Källén, Stockholm University and SWECLIM

2. A scientific goal of climate modeling is the prediction of climate change Ref: IPCC, 2001

3. Regional modeling for details of global change Typical present-day regional model < 50 km Typical present-day global model  200-300 km

4. A typical Swedish regional climate model simulation Limited area domain, nested to a global domain. Atmosphere: @50 km resolution: 106  102  24 grid points (259 488) @20 km resolution: 206  202  24 grid points (998 688) Baltic Sea: @6 nm res. 107  120  41 grid points, 10% active (52 773) @2 nm res. 320  362  41 grid points, 10% active (447 899) 30 years/simulation, with a 10-30 min timestep. Est. # of flops/atmospheric grid point/timestep > 3  10 3. Planned during the next 3 years: Atmosphere @ 10 km, up to 200-year simulations Regional modelling for the Arctic. Also global modelling

5. Climate modeling needs more computing power (ENES, Bryssel, 2001) Purpose est. need of increase Global model resolution 300  50 km100  Feedback (e.g. clouds, carbon cycle)??  Short-term internal variability of climate10  Emission scenarios, parameterizations100  Long-term internal variability of climate10  ------------------------------------------------------------------------------- Sum> 1 000 000  I.e., internationally. This is hardly realistic. Priorities need to be defined and work conducted in international cooperation. Swedish climate modelling participates in international networks for both climate science, model developmnet and climate computing infrastructure. A possible spearhead contribution to international networks could be the use of PC-clusters for climate modelling.

6. On the seven requirements... 1) Comp. Resources: now ~500 000 CPU-hrs/year (Xeon 2.2 GHz-equiv.). 2) Inter- vs. intra-PE comm. speed: Crucial! 3) Primary memory: 1-2 Gb/PE 4) Secondary storage: now ~2Tb operat., ~4Tb archive. 5) Reaccess of stored data: weekly/monthly. 6) Access to databases: National+international. Infrequent exchange of large data sets. 7) Software: exists for T3E, SGI3k, Linux-clusters Planned during the next 1-3 years: Computing resources requirement ~factor 2-10 Secondary storage requirement ~factor 10.

7. An example of inter-PE vs. intra-PE aspects: For Xeon 2.2 GHz (4.8 Gflop/s peak), to use more than 16 PEs requires latency < 8  s bandwidth > 200 Mb/s For Xeon 5 GHz, similar inter-PE requirements apply already if #PEs > 8. Interconnect! If Gigabit - max # of PEs ~30. If Scali -max # of PEs ~120. A generalization: more PEs = faster/more simulations faster network = more PEs can meaningfully be used for a simulation

8. Swedish climate modeling and SweGrid SweGrid of use? Data storage -aspect Additional computing power Software development intresting ”Ensembles” rather than ”high resolution” Arctic modelling: an example of a modelling subtask on the scale of a realistic share of SweGrids for climate modelling. Eventually grounds for a Nordic Virtual Organization, on regional Arctic modelling. Linux-cluster ok Interconnect important! Possible DJF precipitation change by 2071-2100, in %