oceans and climate: an occam perspective andrew c. coward 1 large scale modelling team james rennell...

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

acc@soc.soton.ac.ukhttp://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