Global Land Atmosphere System Study(GLASS)Jan Polcher, Roni Avissar, Peter Cox, Paul Dirmeyer, Hoshin Gupta,
Ann Henderson-Sellers, Paul Houser, Randy Koster, Taikan Oki,
Andy Pitman, Pedro Viterbo

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GLASS is a proposal by GMPP/WGNE, in collaboration with other GEWEX panels and BAHC, to coordinate the development andevaluation of the next generation of complex land-surface schemes.
• The aim is to improve land-surface schemes for the benefit ofnumerical weather prediction and climate models.
• GLASS proposes to achieve these goals by providing a structure to facilitate and promote land-surface scheme (LSS) intercomparisons.

1. Evolution towards the next generationof complex land-surface schemes
The end of the 80’ saw the implementation of the first complex LSSs
in GCMs. The community is currently moving towards the next
generation of complex LSSs.
The higher complexity of the schemes will move them from the statusof GCM parameterizations to that of independent models.
Three workshops have contributed to this evolution :JJII• IGBP/GEWEX, La Jolla, 1997

JI• ECMWF/GEWEX, Reading, 1998

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Quit• GEWEX/INSU, Gif-sur-Yvette, 1999

1.1. New features in the next generation LSSs
The greening of the surface :⇒Introducing the carbon cycle.
⇒Dynamical vegetation.
Vertical vs. horizontal complexity :More emphasis on the horizontal complexity of LSSs :⇒It is needed for surface hydrology.
⇒Model evaluation and data assimilation will benefit.
Land/Atmosphere interactions : Our understanding of thesensitivity of the atmosphere to surface processes needs to be
improved before new feedbacks are introduced.
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Integrator of observations : LSSs will be used in assimilation
mode to construct global datasets of surface variables.

2. Achievements in LSS validation
PILPS :⇒ Established the first generation of complex LSSs.
⇒ Introduced some basic concepts in the community.
⇒ Showed how difficult the coupled problem is.
GSWP :⇒ Raised the question of the meaning of soil moisture at the 1◦ ×1◦resolution.

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What is needed for the next generation ?
⇒ Validate the new processes with off-line point simulations.
⇒ Address the sub-grid variability issues.
⇒ Study the interaction of LSS with the planetary boundary layer.
⇒ Perform coordinated sensitivity experiments with GCMs.
⇒ Help modelers participate in inter-comparison projects.

2.1. From the point to the GCM grid-box.
Land surface schemes are applied from the plot scale to the regional
scale and in a forced or coupled mode.
Because of the high heterogeneity of the surface and the complex interactions between the surface and the planetary boundary layer, it is
not clear how the concepts used by LSS transfer from one application
area to the other.
Soil moisture will be used here as an example to show how thesedifferent applications of LSSs complement each other and how they
contribute to our understanding of surface processes.
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This reasoning also applies to other variables or concepts used inLSSs.

2.2. Soil moisture : local and off-line.
Because of its large spatial heterogeneity soil moisture measurements
are only representative of small areas.
PILPS-2 compared LSSs forced with atmospheric data from available
measurement sites. Soil moisture simulated by LSSs can be validated
at the local scale with in-situ observations.

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Shao et al., 1996, Global and Planetary Change

2.3. Soil moisture : global and off-line.

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In the GSWP experiments LSSs are applied globally at aresolution of 1◦ ×1◦ using observed atmospheric data.
This utilization iscloser to the GCM
application but poses the problem ofsoil-moisture validation.

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Observed soil moisture anomalies may still provide useful information
at these scales.

2.4. Soil moisture : local and coupled.
A single column atmospheric model coupled to a LSS can be used toimprove our understanding of the interactions and to evaluate dataassimilation methods.
DAILY MEAN ROOT ZONE SOIL WETNESS (%)
UNPERTURBED [1/06/87−9/10/87]

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167

182

197

212

227

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Using 4 month ofthe FIFE data theECMWF compareda nudging (NUD)
and an optimal
interpolation (OI)
technique to assimilate 2m temperatureand humidity observations.

40257

272The IO method yields soil moisture values and fluxes which are ingood agreement with observations.
Douville et al., 2000, Q.J.R.M.S

2.5. Soil moisture : global and coupled.
LSSs coupled to GCMs are for instance used to predict the impact ofclimate change on water resources.
A European project addressed this issue by performing time slice
experiments in a doubled CO2 environment with 4 GCMs (4 colors)
coupled to 2 LSSs each .

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The uncertainties in the predicted soil moisture changes over Northern
Europe is caused in part by different sensitivities of the LSSs.
Polcher et al., 1998, GEWEX News.

3. Organization and management
GLASS will coordinate LSS inter-comparisons from local to global
scales and from off-line forcing to fully coupled.
Itwillensure
progress in all applications of LSSs
and advance ourunderstanding
ofthe concepts needed
to represent surface
processes at variousscales.

JJII• The 4 scientific actions will coordinate projects in their field. A
5th action will provide the infrastructure.

JI• The science panel of GLASS will coordinate the 5 actions.

Full ScreenQuit• The science panel will ensure that GLASS contributes to landsurface modelling needs of other GEWEX activities and BAHC.
• WGNE, IGBP/BAHC and the GEWEX panels will be represented on the science panel.

3.1. Local-scale/Off-line action
Coordination : Ann Henderson-Sellers, Andy Pitman

PILPS will continue the phase 2 projects. Next in line is PILPS 2e onthe Torne River Basin. It will validate cold-season processes in LSSs.
Other projects will follow :• A CO2 flux validation with the EuroFlux data from Loobos willbe organized.
• Valdai mature forest data will be used to explore the snow/vegetation interactions.
• A PILPS experiment with ARM/CART data will prepare a parameter estimation exercise and an inter-comparison with a simplified coupling.

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Full ScreenQuit• South Ontario field measurements will be used to validate coldseason processes with high quality data.
Contacts with CSE’s will be established in view of organizing PILPS
experiments in climatic zones not yet used.
PILPS-2e will launch the ALMA activities and set new standards forcollaboration in LSS inter-comparisons.

3.2. Global-scale/Off-line action
Coordination : Paul Dirmeyer, Taikan Oki

GSWP-2 will use the ISLSCP-II data to perform global off-line simulations over a 10 year period. Inter-annual variability of soil moisture
will be the focus.
In the meantime GSWP-1.5 will help prepare phase 2. The following
questions will be addressed :• How Sensitive are LSSs to errors in the forcing data ?
• How well can LSSs be validated at the global scale with remotesensed data ?
• Are the drying out cycles of LSSs comparable ?
• Do LSSs operate in similar soil moisture stress ranges ?
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With the help of a high resolution data the scale aggregation of soil
moisture by LSSs will be explored. It will help understand the meaning of soil wetness at a 1◦ × 1◦ resolution. Data from the Rhône Basinwill be used.

3.3. Local-scale/Coupled action
Coordination : Hoshin Gupta, Paul Houser, Pedro Viterbo

This group will concentrate on the ARM/CART data. It will distribute a simplified single column model and extend the PILPS experiments.
The scientific questions are :• What are the feedbacks between the PBL and LSSs ?
• How does the PBL interact with the surface heterogeneity ?
• Is the sensitivity of the LSS different in off-line and PBL-coupledmodes ?
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The parameter estimation procedure will ensure that the effective
parameters are the same in all schemes.
This action build on PILPS inter-comparisons and will lead into theevaluation of data assimilation methods.

3.4. Global-scale/Coupled action
Coordination : Peter Cox, Randy Koster

Two aspects of land-surface atmosphere interactions are considered
to require model independent assessments :• Climate sensitivity to anthropogenic forcing• Climate variability and predictability.
The first experiment will evaluate the impact of improved surface
conditions on short term forecasts. This will be achieved with a flux
correction of atmospheric fluxes; precipitation in the first phase.
These experiments should yield information on :• The geographical distribution of the strength of the landatmosphere feedback,
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Full ScreenQuit• its inter-model variation,and• its role in the predictability of the hydrological cycle.
The coupled action will maintain close contact with the two AMIP diagnostic sub-projects which deal with the role of LSSs in determining
the quality of the climate simulated by GCMs.

3.5. Advancing(ALMA)

Land-surface

ModelingandAnalysis

Coordination : Jan Polcher, Taikan Oki

The aim is to facilitate the inter-comparison activities within GLASS.
• Provide standards for data transfer. The first version is available
and used by the PILPS and LDAS projects.
• Ensure that data from past experiments remains available.
• Distribute software for the modelling and analysis of land-surface
processesCurrent actions :• Provide LSS drivers based on the interface defined in PILPS-4c :JJIIJI

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http://www.lmd.jussieu.fr/PILPS4c.html• PILPS-2e is currently using the standard data transfer methods.
ALMA provides the technical support for the users.

4. Time line

2001

2002

2003

PILPSC-1

PILPS-CARE

2004

PILPS-2e
Local
off-line

PILPS-2f

Future PILPS ex. (LBA, GAME, SALSA,...)

GSWP-2

GSWP-1.5
Globaloff-line

Validation with remote sensed data
GSWP-aggregation
PILPS-ARM/CART Parameter EstimationModel dist.

Local
coupled

Coupled ARM-CART
Assimilation of in-situ and remote sensed data

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GlobalcoupledALMAEx. design

Coupled predictability ex.
Coupled land-use ex.

Data exchange protocol

PILPS-4c coupler

5. Conclusion
The main innovations GLASS will bring to land-surface intercomparisons are :• Provide a framework which facilitates the inter-comparison andvalidation of LSSs.
• Initiate PILPS type inter-comparisons for simulated CO2 fluxes.
• Integrate the coupling to the atmosphere in the intercomparisons.
• Encourage validation of LSSs with remote sensed data and work
towards data assimilation.
• Establish the role of land-surfaces for the predictability at short
to seasonal scales.
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The following actions will be taken in the next few month

Full Screen• The implementation plan will be finalized before the end of theyear.

Quit• Ensure links with the other GEWEX panels and IGBP projects.