Research
PhD Investigation | Current Work | Conferences & Presentations | Publications
PhD Investigation
Robust Responses of the Ocean Circulation to Climate Change
Supervisor: Dr Arnaud Czaja
Currently, the future projections for ocean behaviour based on the ensemble models from the IPCC archive have too large a spread for any predictions to remain strong against criticism. To increase our faith in climate models, consistent results are needed which both obey the laws of physics and also makes common sense.
One method of achieving this goal is to provide new diagnostic tools that are easy to implement with models. Currently we are developing new theory on the partitioning of heat transport by the ocean and atmosphere from ocean temperature and salinity variations in the ocean: this theory is sufficiently simple to intuitively understand and incorporate into models. By testing these new diagnostic tools and analysing the output, we look into whether the answers are consistent and therefore robust across models.
Current work
Estimating the ratio of Ocean to Atmospheric Heat transport at mid-latitudes from a simple theory involving ocean temperature and salinity
Abstract
Estimates of oceanic and atmospheric poleward heat transport have been published over the years, yet there is generally little agreement over the order of magnitude of the contribution of the ocean and the atmosphere to the total poleward energy transport in middle latitudes. This region is particularly resistant to simple explanations due to the difficulty in parameterizing the heat transport by atmospheric baroclinic waves and ocean eddies, and because of the lack of a simple theoretical framework to predict the heat transport of the large-scale ocean circulation beyond that associated with Sverdrupian (horizontal) gyres (Czaja 2009).
Using a previous expression on the ratio of ocean heat transport to freshwater transport in the atmosphere by Stommel and Csannady (1980), we build up on the theoretical framework to incorporate the ratio of ocean to atmospheric heat transport as a function, solely based on ocean salinity and temperature.
Within the confines of the HadCM3 model we find that our results are within 10% of the model predictions. This equates to roughly an accuracy of 0.1PW for the ocean and 0.5PW for atmospheric heat transport components.
Considering the complexity of the fluid motions and of the diabatic processes (e.g., air-sea interactions, condensational heat release in the storm tracks) associated with oceanic and atmospheric heat transports, the above expression appears as a remarkably powerful and simple relation to compute their ratio.
Running Diagnostics on the CHIME ocean model based at the National Oceanographic Centre (NOC) at the University of Southampton.
Abstract
Current ocean models (eg. HadCM3) use the SI unit of meters as their depth coordinate system. Although a good approximation, the layer depth discretisation scheme gives a non continuous representation of quantities which make eddy parameterisations difficult.
The new CHIME ocean model utilises planes of constant density as its depth coordinate, providing a smoother transition of water mass properties between adjacent grid cells and improving the modelling of mesoscale eddies.
Since the models HadCM3 and CHIME are identical except for their depth coordinate system, it will be of interest to see if properties such as heat and mass transport change given the coordinate system used. As the oceans cover roughly two-thirds of the planet’s surface it is of vital importance to correctly model ocean processes that can regulate local climate processes.
Conferences and Presentations
Ocean-Atmosphere Energy Transport Conference
November 2009, Caltech, California, USA
Ocean Modelling Group Meeting
September 2009, Oxford, UK
Reading Student Conference
July 2009, Reading, UK
Advanced Climate Dynamics Course (ACDC) Summer School
June 2009, Bergen, Norway
Imperial College Atmospheric Physics Group Presentation
May 2009, London, UK
Publications
Dancel, C., and A. Czaja, 2010: A Relation between the T/S Curve and the ration of Oceanic to Atmospheric Poleward Heat Transport in Middle Latitudes, submitted to Journal of Climate.