The OCCAM papers page

This directory contains details of papers and OCCAM documentation. Additional information is also available in the form of posters. Portable Document Format (PDF) versions of many of the posters presented during the project are available from our posters page.

Brief details:

Webb, D.J., and de Cuevas, B.A. 2003:

The region of large sea surface height variability in the southeast Pacific Ocean.

Journal of Physical Oceanography, 33(5), 1044-1056.

Webb, D.J., and de Cuevas, B.A. 2002

An ocean resonance in the Indian sector of the Southern Ocean.

Geophysical Research Letters, 29(14), 9.1-9.4, doi:10.1029/2002GL015270.

Lee, Mei-Man, A.C. Coward and A.J. George Nurser, 2001:

Spurious diapycnal mixing of the deep waters in an eddy­resolving global ocean model.

Submitted to Journal of Physical Oceanography
Currently available: PDF version or just the abstract

Webb, D.J., 2000:

Evidence of shallow zonal jets in the South Equatorial Current region of the Southwest Pacific.

Journal of Physical Oceanography, 30 (4), 706-720. 2000

Fox, A.D., K. Haines and B.A. de Cuevas 1999:

Satellite altimetry data assimilation in the OCCAM global ocean model.

Phys. Chem. Earth (A), Vol. 24, No. 4, 375-380.

D. J. Webb et al (1998): The first main run of the OCCAM Global Ocean Model

Southampton Oceanography Centre, Internal document no. 34.

Abstract:
This report contains background information on the OCCAM global ocean model and the first main run of the model. It includes a discussion of the underlying model equations and information on the model grid, the representation of advection and diffusion, the timestepping scheme and the free surface scheme used by the model.

The report also contains information on how the model was initialised for the first main run, how it was forced, the changes that were introduced during the model run and the format of the archived data sets. The report is available as a Portable Document Format or PostScript file.

P. Saunders et al (1999): Circulation of the Pacific Ocean seen in a global ocean model (OCCAM)

J. Geophys. Res., 104, C8, 18281-18299. (1999).

Abstract:
This paper compares observations made in the Pacific Ocean and the 8-12 year climatology of the OCCAM global model. Meridional mass and heat transports and their divergences are calculated, and zonal averages compared with the air-sea exchange values of Doney et al. [1998] with mixed success. The large scale distribution of sea surface height and near-surface currents are shown to be well reproduced by the model, but their variance is underestimated, severely so in areas of weak variability. Synoptic wind forcing enhances the latter, though only slightly, while higher model resolution improves agreement in areas of strong variability. Model mean transports in the East Australian Current, in the Vitiaz Strait and in the Kuroshio exceed measurements by 10, 0, 18 Sv, respectively, and variability is underestimated by factors between 2 and 4. Near 1000 m and in strong currents the flow is overestimated, but over most of the ocean, model output does not match either the magnitude or the spatial variability of the observations. In contrast, the inflow of bottom water and its spreading path throughout both South and North Pacific is well described. Good agreement is found with measured transport through the Samoan Passage, but at 32°S, east of the Tonga-Kermadec Ridge, the model yields only 60% of the observed value. The Sverdrup balance is shown to hold widely in the model interior. Utilizing the complete depth-integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents.

The report is available as a Portable Document Format or gzipped PostScript file.

Lee, Mei-Man, A.C. Coward and A.J. George Nurser, 2001: Spurious diapycnal mixing of the deep waters in an eddy­resolving global ocean model.

Submitted to Journal of Physical Oceanography
Abstract:
Recent idealized studies have shown that the advection scheme in high resolution z­coordinate models may drive unrealistically high rates of diapycnal mixing. Our aim here is to see whether the diapycnal mixing associated with the advection scheme in a global eddy­resolving (1/4° by 1/4° ) z­level model is sufficiently strong to corrupt the thermohaline circulation. We diagnose the diapycnal fluxes by using the ideas of water mass transformation. In the Southern Ocean, the model deep and bottom waters drift rapidly away from the Levitus climatology, with dense isopycnals moving downwards at rates of up to 35 m/year ; . The strong upward flux (up to 50 Sv) through the dense isopycnals cannot be explained by the incorrect surface forcing (as a result of poor surface fluxes and no ice model) as most of the anomalous diapycnal fluxes are occurring in the deep ocean far from surface forcing. Hence, the excessive diapycnal flux is driven by diffusion in the model, both explicit and implicit. The `effective' diapycnic diffusivity driven by the numerical diffusion (associated with the horizontal advection scheme) is found to be the same order, 1-10 cm²/s , as that driven by the explicit horizontal diffusion. For strong vertical velocities (¸ 20 m/day ) as in models forced by high frequency winds, the vertical advection scheme also gives similar effective diffusivities. These effective diffusivities are considerably greater than suggested by observations. To alleviate these problems, we suggest that eddy­resolving z­level climate models will require (1) less diffusive horizontal advection schemes and (2) better vertical resolution throughout much of the water column.