Climate Modelling Group
School of Earth and Ocean Sciences


Canadian Climate Research Network - Global Modelling

Progress Report: October 1, 1995

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Principal Investigator:
Dr. Andrew J. Weaver
School of Earth and Ocean Sciences
University of Victoria
PO Box 1700
Victoria, British Columbia
CANADA V8W 2Y2

tel: (250) 472-4001
fax: (250) 472-4004
e-mail: weaver@ocean.seos.uvic.ca
___________________________________________________________________

Collaborative Research Agreement at the University of Victoria on Behalf of the Canadian Institute for Climate Studies and Environment Canada (#11 CICS-Global Oceans)

The purpose of the #11 CICS -- Global Oceans grant is to allow Dr. A. Weaver to participate in the continued development of the Canadian Climate Centre (CCC) coupled atmosphere-ocean model and to act as the Scientific Leader of the Ocean Modelling Division of the CCC. In order to accomplish these tasks research grant money is requested to provide secretarial support (Wanda Lewis), teaching relief (Rolf Lueck), Computer Programming Support (Michael Eby) and minor operating expenses. These three people have all now been appointed.

A copy of my progress reports and the original grant proposal are available on the world wide web at:

http://wikyonos.seos.uvic.ca/projects/CCC-Global-Progress.html
http://wikyonos.seos.uvic.ca/projects/CCC-Global-Progress2.html
http://wikyonos.seos.uvic.ca/projects/CCC-Global-Progress3.html

3.2 Global Ocean Modelling

Development of the global ocean model continued during this period, with an investigation of the seasonal cycle, and its relevance to the annually-averaged water mass properties and overturning circulation. In a first phase, a seasonal cycle was added only to the temperature and salinity restoring boundary conditions, and the North Atlantic overturning was found to increase by a few Sverdrups. A seasonal cycle on the winds was then also added, changing the annual mean overturning again by a small amount. Preliminary investigations suggested that variability of the Mediterranean outflow temperature and salinity was an important influence, however parallel experiments in an alternate geometry with no Mediterranean Sea showed that other factors could also be contributing. In particular, large changes in convective patterns near the western boundaries of the oceans under seasonal winds gave rise to concern whether the on/off character of the standard convective parameterization was appropriate for representing seasonal excursions of the mixed layer. Annual and seasonal experiments with the isopycnal and Gent-McWilliams formulations (which can replace convection in regions of steeply-sloping isopycnals) were therefore commenced, but have not yet been fully analyzed due to an unusual numerical problem which is currently being investigated by both Daniel Robitaille and Michael Eby in idealized box models.

Another aspect of the global modelling project has been to assess the equilibrium circulation produced under observed heat and freshwater fluxes and surface wind stresses from the recent da Silva et al. (1994) climatology. Some preliminary treatment was needed to make the fluxes suitable for forcing an ocean model, since the open water bias of the observations caused heat losses in the Arctic to be overestimated. However, even after adjusting the fluxes to be consistent with the climatological ice cover, excessive cooling of the northern oceans led to the dominance of northern deep water formation while southern sinking was essentially suppressed. Resolution is thought to be a major issue here, as suggested by Tziperman and Bryan (1993) and Schiller (1995). It remains an open research question how to improve parameterizations in coarse resolution ocean models enough to resolve this incompatibility. One issue which we are exploring is the suggestion of enhanced vertical mixing in western boundary currents compared to the quiescent interior. For this purpose, we have constructed a stripped-down version of the Bryan-Cox primitive equations model which has no barotropic mode, a linear equation of state, fixed surface temperatures/ densities, and spatially-varying vertical diffusivity, and are currently running tests of the sensitivity of the overturning circulation to inhomogeneous kv in a simple flat-bottomed basin geometry.

Progress continues to be made towards the goal of constructing a global coupled atmosphere-ocean model at UVic. We have received code for the Saravanan and Oregon State University stripped-down atmospheric models, as well as the NCAR AGCM and the GFDL and CSIRO coupled AGCM-OGCMs, and are presently benchmarking these on our machines to determine which are the most appropriate for our requirements.

This summer, we also developed a new statistical model for use in forecasting the migration paths of salmon returning to the Fraser River in southwestern British Columbia for spawning. The technique currently used by the Canadian Department of Fisheries and Oceans is based upon the positive correlation between the diversion of sockeye salmon around the northern tip of Vancouver Island and June SST at Kains Island to the northwest. Multiple regression indicated that the prediction could be both improved by using information from the previous winter as well as spring, and anticipated by as much as four months by combining observations of sea level pressure and SST in winter.

Finally, a preliminary analysis of hydrographic data in the North Pacific, with the goal of studying decadal variability in the mid-latitude barotropic circulation related to secular variations in the tropical ENSO cycle is currently halted due to the conclusion that the data was insufficient for our needs.

References:

da Silva, A.M., C.C. Young and S. Levitus, 1994: Atlas of surface marine data 1994. Volume 1: Algorithms and procedures. NOAA Atlas NESDIS 6. U.S. Government Printing Office, Washington, D.C.

Tziperman, E. and K. Bryan, 1993: Estimating global air-sea fluxes from surface properties and from climatological flux data using an oceanic general circulation model. J. Geophys. Res., 98, 22629-22644.

Schiller, A., 1995: The mean circulation of the Atlantic Ocean north of 30 S determined with the adjoint method applied to an ocean general circulation model. J. Mar. Res., 53, 453-497.

3.2 CFCs and Global Ocean Models

A global version of the GFDL model was run using three different sub-grid mixing schemes: lateral/vertical, an isopycnal mixing scheme (Redi, 1982; Cox, 1987), and the Gent and McWilliams (1990) parameterization. The results from these three runs were analyzed by using CFC-11 as a time-dependent passive tracer, and by comparing with observations. the Gent and McWilliams parameterization improves the CFC-11 distributions when compared to both of the other schemes, especially in the southern ocean, where the "bolus" transport canceled the mean advection of tracers and hence caused the Deacon Cell to disappear. These results suggest that the asymmetric response found in CO2 increase experiments, whereby the climate over the Southern Ocean does not warm as much as in the northern hemisphere, may be an artifact of the particular sub-grid scale mixing schemes used.

The sensitivity of the Gent and McWilliams parameterization was also evaluated by introducing an additional stability dependent diapycnal mixing, following Tandon and Garrett (1995). This additional mixing does not affect the surface buoyancy flux, but do affect the circulation of passive tracers in the deep ocean. These results will be analyzed by looking at the role of boundary layer versus interior mixing.

References:

Cox, M.D., 1987: Isopycnal Diffusion in a Z-Coordinate Model. Ocean Modelling, 74, 1-5.

Gent, P. R. and J. C. McWilliams, 1990: Isopycnal Mixing in Ocean Circulation Models, J. Phys. Oceanogr., 20, 150-155.

Redi, M.H., 1982: Oceanic Isopycnal Mixing by Coordinate Rotation J. Phys. Oceanogr, 12, 1154-1158.

Tandon, A., and C. Garrett, 1995: On as Recent Parameterization of Mesoscale Eddies. J. Phys. Oceanogr, submitted.

3.3 The Canadian Climate High Resolution OGCM

Collaboration with Warren Lee and other researchers in the Canadian Climate Centre has continued. At present, a simplified version of the CCC OGCM has been developed for the purpose of undertaking test simulations. In addition, a new ocean spin-up has been completed and this ocean model will be coupled to the CCC AGCM II to undertake climate change studies.

4. Budget request for the 1995-96 fiscal year:

The budget request remains unchanged from the original request. This original request is detailed below.

1) Continued partial support for a secretary (Ms. Wanda Lewis) $10,000
2) Continued sessional teaching replacement (Dr. Rolf Lueck) $15,000
3) Partial support for one scientific computing Research Associate (Michael Eby) $30,000
4) Operating and Media Costs $10,000
Total: $65,000


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