GASS Projects

GASS Projects are listed below with descriptions and contact information for anyone interested in learning more about a particular project.

Surface drag and momentum transport
Contact: Irina Sandu, Louise NuijensAnnelize van Niekerk

With this project GASS provides the framework for bringing together the observational and modelling communities for efforts to constrain and thereby improve the representation of drag processes.  The idea is to use high and low resolution simulations over some of the most complex mountain chains to identify caveats of blocking and gravity wave drag parametrizations.

The main focus will be on the Himalayas, and, optionally, other complex orography such as the Caucasus. The main questions are:

  • Do the high resolution models agree in terms of the impact of the resolved orography on the flow? (Validation to use these simulations to constrain the parametrizations.)
  • How does parameterized and resolved orographic drag impact the flow in different models?
  • Which common biases, associated with orographic processes, do the models have?
  • How does the large scale dynamics respond to the blocking and GWD parametrization scheme in the various models?

More detailed information on participants and participation, timeline,  etc. can be found here.

Impact of initialized land temperature and snowpack on sub-seasonal to seasonal prediction (ILSTSS2S)
Co-Chairs: Yongkang Xue, Tandong Yao, Aaron Boone

The focus area of the first phase of this project will be the Tibetan Plateau and will be a joint effort with the Third Pole Experiment (TPE) Earth System Model (ESM) inter-comparison project (TPEMIP).
This project intends to address two questions:

  • What is the impact of the initialization of large scale LST/SUBT and snow pack, including the aerosol in snow, in climate models on the S2S prediction over different regions?
  • What is the relative role and uncertainties in these land processes versus in SST in S2S prediction? How do they synergistically enhance the S2S predictability?

This project focuses more on the process understanding and predictability rather than the operational S2S prediction.

More detailed information on participants and participation, timeline, stages, publication etc. can be found here.

Demistify: An LES & NWP fog modelling intercomparison
Contact: Ian Boutle

This GASS project presents an opportunity to form a community and address challenges related to fog modelling.
In the first stage of the project participants are planning a Large-Eddy Simulation (LES) & NWP model inter-comparison using data from the Local and Non-local Fog Experiment (LANFEX, Price et al. 2018).
Key questions to be answered include:

  • How well can models simulate the development of radiation fog?
  • What are the key processes governing the development of radiation fog, i.e. aerosol, cloud microphysics, radiation, turbulence, dew deposition, …?
  • What level of complexity is required from NWP models to simulate these processes?
  • What role does land-surface interaction play in the development of radiation fog?

More detailed information on participants and participation, timeline, stages and publications can be found here.

Improving the simulation of diurnal and sub-diurnal precipitation over different climate regimes
Contact: Shaocheng Xie, David Neelin, Peter Bechtold, Hsi-Yen Ma

As understanding and improving the modeling of diurnal and sub-diurnal precipitation processes can have a broad impact on the fidelity of climate simulations, this white paper proposes a GASS project focusing on improving the model capability through multimodel intercomparison studies against observations.

The overall goals are:

  1. to understand what processes control the diurnal and sub-diurnal variation of precipitation over different climate regimes in observations and models and,
  2. to identify the deficiencies and missing physics in current GCMs to gain insights for further improving the parameterization of convection in GCMs.

Potential Research themes are:

  • Interaction between convection and water vapor
  • Nocturnal convection over land
  • Diurnal cycle of convection over ocean
  • Convection transition

More information on the modelling approach, participation, timelines, coordination with other projects and publication can be found here.

Second phase of the “Grey Zone” project based on the EUREC4A and phase III of GATE field campaigns
WGNE/GASS White Paper on scale-awareness, stochasticity, and convective organization
Contact: Lorenzo Tomassin, Rachel Honnert, George Efstathiouk, Adrian Lock, Pier Siebesma

For the second phase of the “Grey Zone” project it is proposed to investigate (sub-)tropical environments. It is envisaged to have two parts: 1) focusing on shallow convection, and 2) exploring deep convection. Furthermore, we would aim at ambitious high-resolution simulations including “real case” nested large-eddy simulations at O(100m) resolution and global convection-permitting model forecasts of O(5km) resolution.

More information on this project can be found here.

GEWEX Atmospheric Boundary Layer Study 3 (GABLS-3)

Contacts: Bert Holtslag and Gunilla Svensson
GABLS-3 Websites:

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.

GEWEX Atmospheric Boundary Layer Study 4 (GABLS-4)

Contact: Eric Bazile

This GABLS case study examines the interaction of a boundary layer of strong stability with a surface possessing a low conductivity and a high cooling potential, such as snow. The case is explored using observations at the Antarctic Plateau, and the intercomparison involves land-snow surface models, single column models, and large eddy simulations.

GEWEX Process Evaluation Study on Upper Tropospheric Clouds and Convection (UTCC PROES)

Contact: Claudia Stubenrauch

The GEWEX UTCC PROES working group aims to gain a better understanding of the interconnection between the convection and the properties of the outflowing anvils. The focus will be widened to the role of cirrus originating from in situ freezing driven by large-scale forcing, via a link to the Stratosphere-troposphere Processes And their Role in Climate (SPARC) Project.

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

The objective of this project is 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.

Clouds Above the United States and Errors at the Surface (CAUSES)

Contact: Cyril Morcrette and Hsi-Yen Ma

CAUSES is a joint GASS/DOE-RGCM/DOE-ASR project that aims to use observational data from the Atmospheric Radiation Measurement (ARM) program’s Southern Great Plains (SGP) site to understand the role that clouds have in creating the surface temperature error seen over the American mid-west in a number of general circulation models.

Microphysics Project

Contact: Ben Shipway

This project aims to create a better understanding of the differences between 3-D models in different intercomparison cases.

Boundary Layer Cloud Projects

Contact: Adrian Lock

The Boundary Layer Cloud Projects will improve the physical parameterizations of clouds and cloud-related processes and their interactions.

CFMIP-GASS Intercomparison of LES and SCMs (CGILS)

Contacts: Minghua ZhangChris Bretherton, and Peter Blossey
CFMIP Website:

The objective of CGILS is to 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

Contacts: Mikhail Ovchinnikov and Hugh Morrison

The Polar Cloud Project seeks to understand the role of dynamical and microphysical processes and their interactions in mixed-phase Arctic clouds.

Cirrus Model Intercomparison Project

Contact: Andreas Muhlbauer

CMIP investigates 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

The goals of the Grey Zone Project is 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.