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Global Land/Atmosphere System Study (GLASS)


Land-surface modeling has shown rapid development in the past two decades. Where energy and water fluxes were the primary focus of studies in the late 1980s and early 1990s, increasing attention to the global carbon cycle triggered the development of models addressing vegetation phenology, dynamic vegetation structure and carbon pools. In the meantime, improved representations of wetlands, urban areas, interactions between irrigation and ground water, nutrient cycles, cryosphere processes and land properties, and in particular, spectral intervals to enable satellite data assimilation, have continued to be developed. This expanding scope is driven by the growth of interdisciplinary studies of the Earth system. The Global Land/Atmosphere System Study (GLASS) encourages these developments by coordinating the evaluation and intercomparison of the new generation of Land Surface Schemes (LSSs) and their applications to scientific queries of broad interest.

A key objective of GLASS is model development and evaluation and two of its projects address this: The Project for the Intercomparison of Land-Surface Parameterization Schemes (PILPS) for offline point-scale evaluation; and the Global Soil Wetness Project (GSWP-2) for the large global scale (see figure below). Because the land-surface component does not stand on its own and is tightly coupled to the atmosphere in many ways, two GLASS projects address these aspects: the Local coupled land-atmospheric Modelling (LoCo) Project (single column mode); and the Global Land-Atmosphere Coupling Experiment (GLACE) for the global mode.


Rational for a New GLASS Structure

The rapid development of the scientific research agenda calls for a different GLASS organizational structure. The difference between local and global coupling is not straightforward, as many processes that play a role in land-atmosphere interaction have both local and regional aspects. Many feedbacks shown on global maps are partially an expression of local land-atmosphere coupling, which cannot be clearly defined without consideration of interactions with the moving, advecting atmosphere. In addition, it was realized that the realm of data assimilation should get a renewed incentive, as model development and verification increasingly make use of modern statistical techniques and new data. Finally, the development of land models raises the question as to which level the available observations contain enough degrees of freedom to adequately attribute single processes to the overall land state or flux.

In analyzing the structure of GLASS, it was noted that a critical assessment of the expected performance and intrinsic predictability of land processes in models was missing. In addition, GLASS model parameterization and evaluation activities were missing that are necessary for proper assessment of the true added value of land model updates. For this purpose, a protocol needed to be developed in which comparisons of models and data against benchmarks was a key component. To accomplish these new requirements, three new working groups were created: (1) Benchmarking Land-Surface Models and Observations; (2) Model Data Fusion; and (3) Land-Atmosphere Coupling.

Benchmarking Working Group
The goal of this working group is to develop a protocol for evaluation experiments to address the central question: “Does my land-surface model describe the processes in the climate system sufficiently well?” This implies that one needs to define what is “sufficiently well.” Recent studies have compared the skill of state-of-the-art land surface models to statistical models or neural networks calibrated on forcing data alone. This is one example of a test in which we can understand the information content actually added by the land-surface models.

Model Data Fusion Working Group
Activities in land data assimiliation and procedures to calibrate and optimize models by systematic confrontation with observations are the focus of this working group. It will aim at the development of an optiminal system to create global land-surface data sets in which information is extracted from both land-surface models and sophisticated observations.

Land-Atmosphere Coupling Working Group
An important activity of this working group is the estimation of the contribution of memory in the land system to the overall predictability of regional atmospheric phenomena at seasonal time scales. In addition, changes in this predictability under changed climate conditions, and the creation of a systematic hierarchy of levels of land-atmosphere coupling will be coordinated by this working group.

New GLASS Structure

The new structure of GLASS (below) highlights the spatial scales at which the schemes are applied and the degree of interaction allowed with the atmosphere. Four actions which will coordinate intercomparisons in land-surface scheme applications. GLASS includes one transversal action, the Assistance for Land-surface Modelling Activities (ALMA), which provides infrastructure and technical support for the intercomparisons. PILPS continues to address local scales and off-line simulations. GLASS also serves as an interface between the land-surface community (e.g, Land-Use and Climate, Identification of robust impacts - LUCID; Project for Intercomparison of Land Data Assimilation Systems - PILDAS) and other GEWEX projects (e.g, LandFlux).


GLASS is managed by a science panel composed of the leaders of the five actions and representatives of the GEWEX Modelling and Prediction Panel, the International Geosphere-Biosphere Programme (IGBP) Integrated Land Ecosystem–Atmosphere Processes Study (iLEAPS) and the Working Group on Numerical Experimentation (WGNE). Its role is to coordinate the five actions and ensure that all application areas of LSSs benefit from progress made in the various projects.


Dr. Joseph A. Santanello, Co-chair
Hydrological Sciences Branch
Greenbelt, Maryland USA

Dr. Aaron Boone, Co-chair
Centre National de Recherches Meteorologiques


For More Information

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LoCo LoCo - Local coupled land-atmospheric Modelling

PILPS - Project for the Intercomparison of Land-Surface Parameterization Schemes

GSWP-2 (Global Soil Wetness Project)

GLACE-2 (Global Land-Atmosphere Coupling Experiment)

ALMA (Assistance for Land-surface Modelling activities)