発表要旨
1. プロジェクトの目的
This project realized in the frame a MOU between ESC and CNRS, is composed of two main themes sharing the same dynamical core of the ocean: OPA.
First theme: “The impact very shallow ocean mixed layers on the tropical climate intraseasonal variability”. The aim of this work is to get a better understanding and quantification of the resolved upper oceanic structures with small vertical scale that can influence the development of large scale coupled phenomena. Specific objectives will concern the upper ocean equatorial dynamics with a focus on the impact of diurnal cycle and the barrier layer on the tropical climate variability. To carry on this project, the use of an ocean-atmosphere coupled model (OPA9-ECHAM5) with a very high vertical resolution (301 levels) in the ocean.
Second theme: “The impact of sub-mesoscale physics on the North Atlantic balance (heat transport, nutrient cycling, CO2 pump)”: The objective is to get a better understanding and quantification of the contribution of sub-mesoscale physics (eddies and filaments) on the basin scale budgets of heat and salt transport, subduction, (nutrient cycling and production of phytoplankton for the North Atlantic ocean. This requires long term integration (50 years) of an idealized oceanic basin (2000 km x 3000 km) with very high (2 km) horizontal resolution. We use the OGCM OPA coupled with the biogeochemical model LOBSTER. For comparison, we run the same experiment with a range of horizontal resolutions (1°, 1/3°, 1/9°, 1/27°, 1/54°).
2. 今年度当初の計画
Simulations:
First theme: the main goal of this year was to achieve the technical work and the adjustment of the model physics especially for the 301 level configuration. We were planning to perform 2 twin experiments (31 versus 301 levels) of the stand-alone ocean component in forced mode and next 2 twin experiments (31 versus 301 levels) of the ocean coupled to ECHAM5 atmospheric model (T106, 31 levels).
Second theme: The strategy was to proceed in two steps: physics alone and physics coupled with biology. 50 year of spin-up with reduced outputs and online diagnostics, followed by 1 year with complete outputs and diagnostics, for each resolution, for physics alone first, and then for with physics and biology. Implementation of on-line diagnostics for
the budget of T, S, and biological tracers in the mixed-layer
Analysis:
As this second year is focused on achieving the main simulations, the analysis part will remain limited to preliminary exploration.
First theme:
- Validation of the forced stand-alone ocean experiments with available data
- Examination of the impact of the high vertical resolution in ocean forced experiments
- Validation of the large-scale features and variability of the twin coupled experiments
Second theme:
- Examination of the sensitivity of the physics to lateral diffusion
- Examination of the mean state of the thermocline for different resolution
- Examination of the nutrient content of the mode waters
3. 今年度得られた成果
Simulations:
First theme: Tuning and adjustment of the model physics of the stand-alone ocean has been achieved. The numerical stability problems we had in equatorial regions with the 301 levels configuration had been solved by introducing a time splitting for the vertical advection. In addition we switched to a 3rd order upstream-biased scheme for the horizontal advection that is more slightly diffusive than the TVD scheme originally used. Reference twin experiments (31 versus 301 levels) of the forced ocean on recent years (1992-2000) have been achieved. Parallel use of the OASIS coupler has been implemented to speed-up numerical performance of the coupled model. Coupled experiments are in currently in progress, 50(37) years have been done with 31(301) oceanic levels.
Second theme: Both the spin-up simulations and the diagnostics simulations are now completed for the physics alone case. For the coupled experiments, spin-up have been performed for resolutions 1°, 1/3°, 1/9° and1/27°. The spin-up with 1/54° is still to be done. We have also one year with all outputs at 1°, 1/3°, 1/9° and1/27°. The mixed-layer diagnostics for T and S have been implemented in the code and have been runned. The mixed-layer diagnostics for biological tracers have been partially implemented and tested.
Analysis:
First theme: the analyze part was reduced to some first explorations as most of our efforts were focus on the realization of the experiments. Validation of the forced experiment is almost done, its detailed exploration is in progress. The first years of the coupled twin experiment are currently analyzed.
Second theme: analyses of the sensitivity of the physics to lateral diffusion and of the mean state of the thermocline for different resolution are in progress. Preliminary results have been presented. Analysis of the nutrient content of the mode waters has been performed on the low resolution and is the subject of a manuscript in preparation.