Climate Modelling Group
School of Earth and Ocean Sciences

Global Ocean Modelling

CICS - #11 --Global Oceans

Summary of Proposed Research



Andrew Weaver

School of Earth and Ocean Sciences
University of Victoria
PO Box 1700
Victoria, B.C., V8W 2Y2
Canada

Tel: 250-472-4001
Fax: 250-472-4004
http://wikyonos.seos.uvic.ca

Overview

The Canadian Institute for Climate Studies (CICS) Global Oceans project is now in its third year and I am reapplying to the Canadian National Climate Research Committee for a renewal. In this summary, I am providing additional details as to the specific research that will be conducted using CICS funds.

CICS funds were initially used under a joint agreement between the University of Victoria, CICS and the Atmospheric Environment Service (AES) to provide me with additional research time and support to assist the Canadian Centre for Climate Modelling and Analysis (CCCma) in developing global ocean general circulation models (OGCMs) for the purpose of coupling them to the CCCma atmospheric general circulation model (AGCM). The initial phase of this project is now complete in that a fully-coupled AOGCM has been developed by the CCCma. This coupled model has now been used to undertake climate change experiments.

The building and improving of the coupled model is a continuous process and it is for this reason that I am seeking continued support for the project. While an OGCM has been developed (in collaboration with Warren Lee at the CCCma) we are now seeking methods for improving this model through the incorporation of improved numerics and subgrid scale parameterizations as detailed below.

Michael Eby is currently employed as a full time programmer/Research Associate in my lab to develop improved global ocean models for the purpose of undertaking climate change experiments. We are coupling these new OGCMs both to our locally-developed atmospheric energy-moisture balance model (EMBM) and, via technology transfer to the CCCma, to the CCCma AGCM. His duties include the development of new numerical schemes to handle advection, the implementation of new subgrid scale mixing schemes, and the undertaking of numerous sensitivity studies to various model parameterizations. The knowledge gained from these experiments is transferred to the CCCma modelling groups through discussions at our weekly coupled modelling meetings.

Unlike other network proposals which fund teams of researchers across Canada, this proposal has only one principal investigator. The CCCma moved to Victoria to take advantage of local expertise in ocean modelling. In particular, I have been heavily involved in the development of the new coupled model through both the participation in weekly coupled model meetings and the development, testing and experimenting with various global ocean models and simple coupled models. The purpose of this proposal is therefore to take advantage of the unique opportunity afforded by my proximity to the CCCma modelling group. The CCCma does not have extensive ocean modelling expertise within their division yet the OGCM is a crucial component of the coupled model. By maintaining strong expertise in ocean modelling down the hall from the CCCma we will be able to continue our fruitful collaboration into the development of the next generation of ocean models.

I recently received notification that I was awarded a Steacie Fellowship for the period 1997-1999 and hence no longer need to request teaching relief from the CICS. As such, my requested level of research grant funding is now $50,000. This will allow for the full support of Michael Eby as well as partial support for my systems manager (D. Robitaille). As I will now be able to spend 100% of my time undertaking research, I expect my productivity to be enhanced still further over the next few years.

Scientific Goals

While at the University of Victoria my research group and I have invested a large amount of effort to develop an atmospheric model suitable for coupling to ocean models, for the purpose of undertaking the long-timescale integrations required to investigate climate variability on the decadal-millennial timescale. To this end we have coupled to a newly-developed EMBM, into which a thermodynamic ice model has been incorporated. We have also recently incorporated a parameterization which allows for wind stress feedbacks. The virtue of the atmospheric component of the coupled model is that we do not need to employ flux adjustments to keep the simulation of the present climate stable. Thus, it is ideally suited for both climate and paleoclimate modelling. This fully-coupled model will be released to the climate modelling community along with a user manual by August 1997 via our web site (http://wikyonos.seos.uvic.ca). We foresee releasing a parallelized version of this code towards the end of 1999.

In the first area of proposed research we will use the coupled model to try and understand the regional and global impacts of using flux adjustments in more complicated atmosphere-ocean models. This will be accomplished by conducting global warming simulations, with and without flux adjustments, and comparing the resulting model fields. During the course of this research we also expect to be able to develop techniques for reducing these flux adjustments. The knowledge gained from this research will be transferred to the CCCma through our weekly coupled model meetings. This research will be of great benefit to the CCCma as one of their short term goals is to try and find ways of minimizing the flux adjustments currently used.

In the second area of research we will continue to explore the effects of using improved numerical methods for handling advection in the GFDL ocean model. This will be accomplished by undertaking global coupled and uncoupled model experiments (with and without the Gent and McWilliams parameterization for mesoscale eddies) which use a variety of advection schemes (including the flux-corrected transport scheme). The individual experiments will be analysed in an attempt to make recommendations to CCCma recording the numerics and mixing schemes to be used in the next generation ocean model.

The North Atlantic Ocean is fundamentally linked with the rest of the world's ocean via communication through the Antarctic Circumpolar Current (ACC) and the Southern Ocean. The extent to which processes occurring in the North Atlantic affect the circulation in other oceans and vice versa is still unknown. A fundamental question regarding the North Atlantic and its relationship with the rest of the world's oceans concerns the reason why the North Atlantic forms deep water yet the Pacific does not. Many geographical clues also exist regarding the asymmetry of the thermohaline circulation in the two oceans. The first and most obvious one is that the North Atlantic extends farther north than does the Pacific, and has a deeper connection with the Arctic. Furthermore, the Pacific is twice as wide as the Atlantic. The narrow Isthmus of Panama at low latitudes allows westward freshwater export via the trade winds, while the Rocky Mountains block an opposite flow at higher latitudes. The narrower width of the Atlantic compared to the Pacific would cause a greater fraction of its area to be susceptible to the incursions of cold dry continental air that favour evaporation. Within the ocean, the salty Mediterranean outflow assists in preconditioning intermediate water flowing into the Norwegian Sea to undergo deep convection, as does the exchange with South Indian waters off the Cape of Good Hope. Finally, it has been hypothesized that the poleward extension of South America compared to South Africa might impede the transport of freshwater out of the Pacific by the ACC.

The global coupled EMBM-TIM-OGCM will be used to try and unravel which of the different mechanisms is the most crucial in determining the observed preference for deep water formation in the Atlantic instead of the Pacific. This project will point to the fundamental processes governing the present day ocean climate and hence will underline the importance of various components of the ocean model which is being used by the CCCma.

In using ocean models it is also fundamental to understand the processes involved in the real ocean and how they are parameterized in these models. To this end, in my final area of proposed research, I would like to investigate how oceanic mixing in boundary layers, versus the interior of the ocean, affects the large-scale thermohaline circulation. More specifically, previous attempts at modelling the ocean's large-scale thermohaline circulation have ignored the observation that diapycnal mixing in the ocean is enhanced near lateral boundaries. I have already invested a great deal of intellectual effort in setting the stage for examining this problem and I am eager to carry it through to its completion. This problem is fundamental to ocean dynamics and the role of the ocean in climate since the oceans thermohaline circulation so critically depends on the parameterization of diapycnal mixing. It will also be of importance to the CCCma as I may be able to develop improved subgrid scale mixing parameterizations for incorporation into the next generation CCCma ocean model.

The specific deliverables of this research grant proposal are therefore:



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