UJCC climate models

UJCC is making use of a broad group of models in order to systematically explore the role and value of resolution in climate system research: starting with the base N96 AOGCM (HadGEM1), an array of coupled and uncoupled models has been set up, in order to test hypotheses about the global impact of increasingly resolving the fundamental building blocks of climate. This model "matrix" will be an invaluable resource for understanding the impact of resolution in both atmosphere and ocean model components, and will help to guide future model development.

All these models have as their baseline science that of the initial reference HadGEM1a models used at the Hadley Centre. These build on the IPCC AR4 version of the model, and include various small improvements to the science and fixing of known problems.

See http://www.higem.nerc.ac.uk/higem_only/validation/hadgem1a/hadgem1a.html for more details of HadGEM1a.

The following figure illustrates the role of resolution in climate modelling. In this figure, model clouds have been drawn with a grey/white colour scale, while precipitation has been overlaid in red. The model-produced information is shown on a global map. The impact of resolution can be discerned by analogy, noticing how the left panels remind us of a picture taken with a cheap digital camera, where the individual pixels are visible; as resolution increases, the pixels are smaller and the image is of higher quality. In climate modelling, at lower resolution, many of the climate elements (e.g. weather fronts, organised convection) are not properly resolved, so that their characteristics are only approximative and their interaction with other climate elements is only partially possible. Their impacts (e.g. high winds, extreme precipitation) are only partially included in the climate simulation. At higher resolution it is possible to see how weather fronts are narrower, how regions of convection seem to have more coherent structure and how large regions of intense precipitation emerge.

The value of high resolution in climate system research

The UJCC team work alongside Japanese scientists at the Earth Simulator Centre and at the University of Tokyo, who have also developed models at high and ultra-high resolution to solve climate problems.  It is beneficial to make use of a broad group of models of varying resolution (and model science) in order to explore the role and value of resolution in climate system research, particularly at the regional scale.  Because of the way certain processes and feedbacks are modelled, different GCMs may simulate quite different responses to the same forcing.  The inter-comparison of models is essential to achieve the most reliable climate simulation, and will also help to guide future model development.  

UJCC achievements

In the first two years, UJCC have made the following contributions to UK climate system research:

• Demonstration of the importance of resolution for capturing tropical cyclones and extreme weather events.
• Use of a matrix of models (outlined on the right) to provide significant advances in the understanding of the influence of model ocean and atmosphere resolution on the simulation of climate phenomena, such as El Nino, and on model errors.
• Detailed studies of land-atmosphere interactions and the sensitivity of soil moisture, especially with respect to the Asian Summer Monsoon.
• The production of high quality movies of global weather systems from NUGAM simulations, in collaboration with the NASA Earth Observatory.

Coupled models 

HadGEM1: The Hadley Centre's HadGEM1 model, successor to the famous HadCM3, is normally run with an atmospheric resolution of (1.88x1.25, ~135 km in mid-latitudes) and was recently integrated for hundreds of years within the framework of IPCC AR4. In the ocean, this coupled model is integrated with a grid spacing of 1x1 (1x0.333 in the tropics).

HadGEM1a status on the ES can be seen at:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Hadgem1aPd

NERCs UK-HiGEM project has developed, in collaboration with the Hadley Centre, a higher resolution model, pushing resolution to 1.25x0.83 (90km) in the atmosphere and 0.3x0.3 (30 km) in the ocean. HiGEM1a status on the ES can be seen at:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Higem1aPd

Cross-coupled models:  

With these models established on the ES, two further models combining their resolutions have also been developed.

The HadGEM1 atmospheric resolution model (135km) has been coupled to the HiGEM ocean model (30km). Hadgem1a3rdDegOcnPd status on ES:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Hadgem1a3rdDegOcnPd

The HiGEM atmosphere model (90km) has been coupled to the HadGEM1 ocean model (90km). Higem1a1DegOcnPd status on ES:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Higem1a1DegOcnPd

In order to fully exploit the power of the Earth Simulator, the Nihon-UK Global Environmental Model (NUGEM) was co-developed by the UKMO Hadley Centre and by NERCs NCAS-CGAM. The atmospheric model, NUGAM, is an N216 model(0.83x0.56, corresponding to ~60 km in mid-latitudes), the resolution of the weather forecasting global model which was operational at the UK Met Office until December 2005. The ocean model component is the same 30km model as in HiGEM. NUGEM1a status on ES:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Nugem1aPd

Uncoupled models (AMIP2 simulations)

Atmosphere-only versions of the HadGEM1, HiGEM and NUGEM models, using AMIP2 forcing of the sea-surface temperature and sea-ice, have also been integrated on the ES. These allow us to understand how the behaviour of the atmosphere changes as resolution is increased, with the forcing from the ocean remaining consistent.

HadGAM1a status on ES:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Hadgam1aAMIP2Pd

HiGAM1a status on ES:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Higam1aAMIP2Pd

NUGAM1a status on ES:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/Nugam1aAMIP2Pd

There have also been a variety of other integrations, including using SSTs derived from the coupled HiGEM model to drive the atmosphere-only model. These can be found from the Models section of:

http://www.cgam.nerc.ac.uk/pmwiki/ES/index.php/Main/HomePage