The oceans and sea-ice play an important part in the global climate system. In particular, the large thermal inertia of the oceans, and the consequent long timescales of adjustment, means an accurate representation of ocean processes is critical for realistic climate simulation. For many years, in the Hadley Centre and elsewhere, the relatively coarse horizontal ocean resolution used has meant these models have had to adjust the heat and freshwater fluxes at the ocean surface to produce realistic simulations. In the latest HadCM3 version of the model, a 1.25° ocean grid is used and heat and freshwater transport processes are better represented than before. This has been a major factor in the ability of the model to run without the need for flux adjustments.

The ocean component of HadCM3 contains the following features: a 1.25° x 1.25° latitude/longitude grid with 20 vertical levels, Gent and McWilliams (1990) mixing as implemented by Visbeck et al (1997), a hybrid Kraus Turner and K-theory mixing scheme, a simple overflow parametrization and Levitus (1994) initial ocean temperature and salinities. The coupled model has been run for over 1000 years and has been extensively used in climate change simulations.

Ongoing research in the Global Ocean and Sea-Ice Modelling Group includes:

• development of the 1.25° x 1.25° global ocean model used in coupled climate simulations;
• study of the sensitivity of the ocean circulation to the choice of model parametrizations;
• study of North Atlantic decadal variability in the HadCM3 model and in observations;
• development of a global coupled model, comprising a 40 level 1/3° eddy-permitting ocean model and a 2.5° x 3.75° atmosphere model;
• configuration of a 1/3° resolution Atlantic Ocean model for studying parameter sensitivity and for comparison with the 1.25° resolution model;
• improvement to the representation of thermodynamic and dynamic sea-ice processes including the implementation of an elastic-viscous-plastic ice dynamics;
• ocean carbon cycle studies.

For more details, click on the following links:

• ocean model development;
• sea-ice model development;
• eddy-permitting global ocean model;
• decadal variability in HADCM3;
• ocean carbon cycle studies.
  
  

The Ocean Model Validation and Techniques Group performs two tasks. In our validation work (which is part of the programme of the Hadley Centre for Climate Prediction and Research) we confront the climate configurations of the ocean model with our knowledge of the real world, derived from oceanographic observations of many kinds. The aim is to assess how well the model is performing for key oceanic aspects of the climate system, and to understand any important discrepancies between the model and the observations. The ultimate aim of this understanding is to help us develop improved climate models and so reduce uncertainty in climate projections.

The group also co-ordinates technical developments to the Met Office's Unified Model (UM) ocean code. This code is used by all the ocean modelling groups in the Met Office, and some outside, and provides a flexible modelling environment for a wide range of deep ocean modelling applications.

Some examples of current topics of the group's work are listed below and can be found by clicking on the following links.

• thermohaline circulation;
• ventilation and intermediate waters;
• vertical mixing;
• technical development and system management.