2. Oceans and climate: an OCCAM perspective Andrew C. Coward 1 Large Scale modelling team James Rennell Division for Ocean Circulation and Climate Southampton Oceanography Centre 1 OCCAM team: David J. Webb, Beverly de Cuevas, Yevgeny Askenov Isopycnic team: Adrian New, Yanli Jia, Alex Megann, Bob Marsh acc@soc.soton.ac.uk http://www.soc.soton.ac.uk/JRD/LSM

3. Outline The ocean's role in climate Current concerns and uncertainties The OCCAM global ocean model Computational aspects Post-processing requirements The way ahead

4. Major components of the climate system From Crowley and North 1991

5. Timescales for different components of the climate system From Crowley and North 1991

6. The Earth's radiation and energy budget

7. Latitudinal distribution of net radiation +ve

9. A typical overturning streamfunction (Sv) Depth (m) LatitudeNorthSouth Global Atlantic only

13. Z-level ocean general circulation models Bryan-Semtner-Cox 1969, 1974, 1984

14. Z-level ocean general circulation models Bryan-Semtner-Cox 1969, 1974, 1984 Fine Resolution Antarctic Model (FRAM) 1988-1992 Cray XMP/YMP autotasking parallelism 8 processors memory slab window with SSD asynchronous "putwa's and getwa's"

15. Z-level ocean general circulation models Bryan-Semtner-Cox 1969, 1974, 1984 Fine Resolution Antarctic Model (FRAM) 1988-1992 GFDL Modular Ocean Model (1990, 1994,1999)

16. Z-level ocean general circulation models Bryan-Semtner-Cox 1969, 1974, 1984 Fine Resolution Antarctic Model (FRAM) 1988-1992 GFDL Modular Ocean Model (1990, 1994,1999) Parallel Ocean Program (POP) 1992- OCCAM (1994-

17. OCCAM model development route

18. Performance comparison: OCCAM vs JAMSTEC (MOM 2) OCCAM : 1/4x1/4 o truly global ocean model, 36 vertical levels requires: 24 hours per model year using 128 T3E processors JAMSTEC : 1/4x1/4 o ocean model 75 o S to 75 o N, 55 vertical levels requires: 108 hours per model year using 10 NEC SX-4 processors suggesting: 1 SX-4 node = 4-5 T3E processors

19. OCCAM 1/4 x 1/4 o global ocean model Bryan-Cox + Twin-grids for truly global coverage. Pacanowski and Philander vertical mixing Free surface code Improved advection scheme (modified split-quick) Improved vertical advection of momentum Re-written for massively parallel processing. 14 model years integration with monthly mean winds (ECMWF, 1986-88 climatology) Starting from rest with Levitus '82 climatological values. 4 years with relaxation at all depths (initially to Levitus '82, Levitus '94 after day 180) Monthly mean Levitus values used to relax surface temperature towards climatology Salinity difference converted to a freshwater flux which affects the sea surface height. Full restarts saved every 15 days throughout; Every 3 days for last 2 years Other runs include: 5 year control run with 6 hourly ECMWF wind-stresses and pressure (1992 onwards) 5 year run with 6 hourly ECMWF wind-stresses and assimilation of T/P altimeter data True "running means" stored at 5 day intervals. OCCAM 1/8 x 1/8o global ocean model: Started from 8 model year state of the 1/4 o model Two model-year integration completed, Full restarts saved every 10 days

20. Sea surface temperature: OCCAM 1/4x1/4 o global model

21. SOC-CSIRO Ocean Atmosphere ProgrammE (SCOAPE) Top-level communication subroutines in use between SCOAPE components

22. Compute resources At SOC: 400GB on-line data 12 processor Origin 2000 Large memory SGI R10,000 and Sun Ultra 10 workstations National centre (Manchester): O(1TB) near-line storage O(100GB) on-line 776 Processor Cray-T3E 1200 16 processor Origin 2000 post-processing machine 8 processor Fujitsu VPP300