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Oceans and climate: an OCCAM perspective
Andrew C. Coward1
Large Scale modelling team
James Rennell Division for Ocean Circulation and Climate
Southampton Oceanography Centre
1OCCAM team:
David J. Webb, Beverly de Cuevas, Yevgeny Askenov
Isopycnic team:
Adrian New, Yanli Jia, Alex Megann, Bob Marsh
[email protected]://www.soc.soton.ac.uk/JRD/LSM
Outline
• The ocean's role in climate
• Current concerns and
uncertainties
• The OCCAM global ocean model
• Computational aspects
• Post-processing requirements
• The way ahead
Major components of the climate system
From Crowley and North 1991
Timescales for different components of the climate system
From Crowley and North 1991
The Earth's radiation and energy budget
Latitudinal distribution of net radiation
+ve
A typical overturning streamfunction (Sv)
Dep
th (
m)
Dep
th (
m)
LatitudeNorth South
Global
Atlantic only
Space
IceIncoming SWOutgoing LW
South NorthUpwelling(S. Ocean)
Tdeep "Deep Ocean"
100m
Fixedlocation
Variablelocation
One- dimensional (meridional) energy balance modelwith specified oceanic "Thermohaline" circulation
20
0
- 20
- 40
- 60
- 80
- 100
- 120
0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9
Hysteresis due to varying ice albedo
Gl o
bal M
ean
Tem
pera
t ure
(C
)
Ice Albedo
Snowball Earth
Typical values
Z-level ocean general circulation models
•Bryan-Semtner-Cox 1969, 1974, 1984
Memory slabwindow
I
J
K
Z-level ocean general circulation models
•Bryan-Semtner-Cox 1969, 1974, 1984
•Fine Resolution Antarctic Model (FRAM) 1988-1992
Cray XMP/YMP autotasking parallelism8 processorsmemory slab window with SSDasynchronous "putwa's and getwa's"
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)
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-
MOM
MOMA
MOMA-MPI
Master
Slave Slave
Slave
SlaveSlave
Slave
Slave
OCCAM
OCCAM model development route
Performance comparison: OCCAM vs JAMSTEC (MOM 2)
OCCAM : 1/4x1/4o truly global ocean model, 36 vertical levels requires:
24 hours per model year using 128 T3E processors
JAMSTEC : 1/4x1/4o ocean model 75oS to 75oN, 55 vertical levels requires:
108 hours per model year using 10 NEC SX-4 processors
suggesting: 1 SX-4 node = 4-5 T3E processors
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 climatologySalinity 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 dataTrue "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
Sea surface temperature: OCCAM 1/4x1/4o global model
SOC-CSIRO Ocean Atmosphere ProgrammE (SCOAPE)
Top-level communication subroutines in use between SCOAPE components
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
