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GEWEX Modeling and Prediction Activities

Two GEWEX Panels, GASS and GLASS, oversee GEWEX modeling and prediction activities, which include development and improvement of boundary layer, cloud and land-surface parameterization schemes to ensure their successful integration into global circulation models.

The co-chairs of GASS and GLASS are members of the Working Group on Numerical Experimentation (WGNE), which is jointly sponsored by the World Climate Research Programme and the World Meteorological Organization Commission for Atmospheric Sciences. WGNE leads the development of atmospheric models for both climate studies and numerical weather prediction.




The Global Atmospheric System Studies (GASS) Panel facilitates and supports the international community who carry out and use observations, process studies and numerical model experiments with the goal of developing and improving the representation of the atmosphere in weather and climate models. Primarily, GASS coordinates scientific projects that bring together experts to contribute to the development of atmospheric models.

Co-chairs: Jon Petch and Stephen Klein

GASS Science Steering Committee and Terms of Reference

Subscribe to the GASS E-mail List

The 1st Pan-GASS Conference was held on 10-14 September 2012 in Boulder, Colorado, USA, and focused on observing, understanding and modelling atmospheric physical processes. The final conference program with links to the plenary presentations is available on the conference website.

GASS Projects Description

GEWEX Atmospheric Boundary Layer Study (GABLS-3)

Contacts:  Bert Holtslag and Gunilla Svensson

GABLS-3 Websites:

GABLS-4 Website:


GABLS coordinates research on boundary layer physics to improve the representation of the atmospheric boundary layer in models.

The GABLS-3 large-eddy simulation (LES) intercomparison case is based on a moderately stratified, baroclinic, mid-latitude boundary layer observed over Cabauw, the Netherlands on 1 July 2006.

Vertical Structure and Diabatic Processes of the Madden-Julian Oscillation -- A joint project with the MJO Task Force using YOTC data

Contacts: Xianan Jiang and Prince Xavier


To understand the role that convection, cloud, radiative and dynamic processes play in the development and evolution of the MJO in order to achieve better fidelity of the MJO in global prediction models.

Convective and Cloud Processes During TWP-ICE: A Multi-Model Evaluation Project

Contacts: Ann Fridlind and Jon Petch


To understand the large-scale controls on tropical deep convection properties, including convective scale vertical velocity and stratiform vs. convective partitioning.

Microphysics Project

Contact: Ben Shipway


To better understand the differences between 3D models in different intercomparison cases.

Boundary Layer Cloud Projects

Contact: Adrian Lock


Improve physical parameterizations of clouds and cloud related processes and their interactions.

CFMIP-GASS Intercomparison of LES and SCMs (CGILS)

Contacts: Minghua Zhang, Chris Bretherton, Peter Blossey


CFMIP website:


Improve understanding and simulation of boundary-layer cloud feedbacks on climate through intercomparison of LES and
single-column models forced by idealized climate perturbations.

Polar Cloud Project

Semi-Direct Aerosol Campaign (ISDAC) Mixed-Phase Arctic Clouds Project

Contacts: Mikhail Ovchinnikov and Hugh Morrison


To understand the role of dynamical and microphysical processes and their interactions in mixed-phase Arctic clouds.

Cirrus Model Intercomparison Project

Contact: Andreas Muhlbauer

To investigate the microphysical and macrophysical evolution and life cycle of a synoptically driven cirrus and to compare simulated cirrus cloud properties and radiative effects among models.


Grey Zone Project
: Cold Air Outbreak Intercomparison Case

Contact: Pier Siebesma

To systematically explore the capability of climate and weather models to represent cloud and convective processes in the resolution range between 1 and 10 km (the so called grey zone) in support of the development of scale adaptive parameterizations for these processes. As a first activity, a comprehensive intercomparison case for a cold air outbreak such as observed during the CONSTRAIN field campaign has been developed.

Other GASS Projects


Continuous Intercomparison of Radiation Codes

Contacts: Lazaros Oreopoulos and Eli Mlawer


CIRC is intended as an evolving and regularly updated reference source for evaluation against "line-by-line" standards of radiative transfer codes used in Global Climate Models and other atmospheric applications. CIRC differs from previous intercomparisons in that it relies on an observationally validated catalogue of cases. It is currently completing Phase I.


See the Core Group on Theoretical Studies of the Convection Parameterization Problem if you are interested in joining a European effort for strengthening the theoretical basis of physical parameterizations.