After WOCE what are the remaining challenges and how should we set about meeting them?

After WOCE

what are the remaining challengesand how should we set about meeting them?

Jürgen Willebrand, IfM Kiel

Input appreciated from:G. Holloway, P. Killworth, W. Large

J. Marotzke, T. McDougall, J. SarmientoR. Schmitt, P. Rhines, C. Wunsch

Thanks to A.Biastoch

WOCE and beyond, San Antonio 2002

WOCE Goals

Goal 1:

to develop models for predicting climate change,collect data necessary to test models

Goal 2:

to determine representativeness of WOCE data sets for long-term behavior of the ocean, and to find methods to determine long-term changes


WOCE Achievements (short version)

to 1:

- models greatly improved (but far from perfect) - WOCE data give unprecedented view of global ocean but important gaps in understanding remain- test of models against data usually qualitative

to 2:

- large variability on interannual/decadal time scales found- much progress with technologies to determine long-term changes


What else has changed since 1980 ?

Better understanding of

• role of ocean circulation for climate

• record of past changes

• role of circulation for biogeochemistry / ecology

• role of other parts of earth system for global change

• global change has arrived


View of SurfaceTemperature Changes 1000 – 2100

Past and projected surface temperature anomalies - Mann et al reconstruction- Instrumental record- IPCC scenarios

J. Gould


Goals for post - WOCE research

Goal 1:

to develop ocean models for simulating past and future changes in ocean circulation, climate and environment,collect data as necessary to test models

Goal 2:

to continuously and adequately observe the ocean on a global basis


Goal 1 specific objectives

1. to understand ocean processes/mechanisms relevant for ocean circulation variability at all time scales (PO-community)

2. describe and understand large-scale ocean variability at all time scales, and its role for climate (PO with climate and paleo communities)

3. understand interaction of ocean circulation with environmental changes (PO with biogeochemical / ecological communities)


1. Understanding processes / mechanisms

a) Mixingb) Effects of mesoscale eddiesc) Interaction with topography

d) improve air-sea fluxese) is ocean in equilibrium with 20th century forcing?f) relation convection - sinkingg) interaction w. sea-ice

. . .

z) Energy balance of circulation

To be addressed by process experiments, theory, modeling ...

Where applicable, ‚understanding‘ should eventually translate into physically-based parameterizations for models!


processes / mechanisms cont’d

a) Mixing

- How is the mixing distributed in the ocean? How can we find out? Consequences of spatial variations?

- Dynamics and energetics (local/global) of mixing?

- Under which conditions diffusivities for T/S are different?

- On what time scales mixing becomes important for circulation changes?

- Which mixing processes support the THC? Where do they occur?



b) Effects of mesoscale eddies

- eddy tracer transports (bolus transport, pv vs. layer thickness diffusion ...) local vs. non-local effects

- momentum exchange with mean circulation

- connection of lateral stirring with diapycnal mixing?

- percentage of eddy energy used for diapycnal mixing

- parameterizations of sub-mesoscale processes



c) Interaction of circulation with topography - parameterizations of unresolved topography

- barotropic recirculations

- flow through straits

- slope convection

- ...

Denmark Strait pot.density (R. Käse)


Overflow representation effects large-scale overturning

Kleine BildunterschriftText

J. Dengg


2. Describe/understand large-scale variability and ocean’s role in climate

CLIVAR organization along time scales:Seasonal - Interannual:

El Nino, Monsoon systems ...emphasis on predictability / prediction

Decadal - centennial: - Subpolar/subtropical circ: response to atm. forcing patterns (e.g. NAO) - Cross-equatorial transports/cells, coupling w/ extratropics - thermohaline circulation...Data from combination of observations, analysis of historical data sets, reconstructions from proxy- data (e.g. corals, tree rings, ..)

Anthropogenic climate change: prediction + detection


North Atlantic overturning in climate change simulations (IPCC 2001)

THC evolution in greenhouse scenario: large model dependence

Good argument for

- modelers to improve their models

- observers to start measuring THC change


THC evolution in greenhouse scenario: large model dependence

Latif et al. (2000)

Latif (2002, pers. comm.)

Ocean modelresponsible for difference?


Labrador Sea convection may stop even in stable THC scenario

U.Schweckendiek (2002, pers. comm.)


Role of ocean for climate variability

Tropical oceans:- dominant influence on seasonal/interannual var. (e.g. El Nino)- strong influence also on decadal extratropical var. (e.g. NAO)?

Mid-latitude oceans:- very little influence on interannual-decadal var. (except through heat storage)- some influence on interdecadal var. ?

Recently:- role of ocean heat transport challenged by atmospheric modelers

but:- thermohaline circ. dominant for centennial/millenial var. ?


Centennial-millenial climate variability during last glacial

Temperature from sediments and ice cores (Rahmstorf, 2002)

Millenial time scales (not part of CLIVAR)allow view of different dynamical regimesopens possibility to obtain long-term perspective

so far most explanations involve thermohaline circulation changes„Physics of most paleo-models is unimpressing“


3. Interaction ocean circulation – environment

Understand role of ocean circulation for

- transport of radiatively active gases (CO2, methane) - natural carbon cycle and anthrop. perturbation- ocean ecosystem/biological pump

- natural variability and response to greenhouse warming

joint observations where possibleforward/inverse modeling of joint system

Help interpreting paleo-record by modelingpaleo-proxies (e.g. 13C, 18O), sedimentation rates..


OCMIP-2: Anthropogenic CO2 Flux, Storage and Transport

Large model dependence


Resolution Dependence of Anthropogenic CO2 Flux

(poster Biastoch et al.)

4/3° resolution 1/3° resolution

December 1989, in mol/m∆/yr


Simulated Surface Chlorophyll in an Eddy-resolving model

A.Oschlies


Can we learn from biol. distributions about ocean physics?

A.Oschlies

SeaWiFS surface chlorphyll 10S-12S during 1998 Rossby wave propagation(Kawamiya and Oschlies, 2002)


Ocean model development

- parameterization of subgrid-scale processes- models should be sufficiently adiabatic

- what resolution is sufficient for a) convergence of coupled climate integrations? b) convergence of eddy energy / WBC structure? c) convergence of biological production? d) convergence of eddy stirring effects? e) numerical convergence?

- model errors should be quantified- model hierarchies helpful- same circulation models for physical oceanography, biogeochemical and paleo applications

- software engineering


Observing System(s)

- design: follows from objectives and techn./econ. possibilities climate prediction climate change detection ocean prediction (e.g. ecosystem) understanding ocean variability applications ..

- should evolve with technological advances

- should stay close to assimilation activities


Combining observations and models (assimilation)

- obtain global state estimation on ongoing basis

- develop robust methods that work a) with non-Gaussian statistics b) with chaotic models

- include biogeochemical state variables

Proof of the (assimilation) pudding is in the eating!

The End

After WOCE what are the remaining challenges and how should we set about meeting them?

Documents

Transcript of After WOCE what are the remaining challenges and how should we set about meeting them?