Updated: June 1, 2004

Overview

Interaction between Atmosphere and Ocean

Climate change comprises a number of interactive elements. On the ocean, when clouds form and rain falls the sea surface temperature changes. As the results from those interactions, changes of the flow of ocean currents or oceanic state will bring climate change with long-range time scale. Sea ice in Arctic and Antarctic is implicated in these climate changes, and influence maintaining mild temperature variability at the polar regions. Land surface topography, glaciers, forests and other vegetation, volcanic activity, the activity of rivers, as well as human activities, all exert a influence on climate change.

Due to the fact that any attempt to model all of the above interactive factors would be extremely complicated, the atmospheric (parameterized cumulus processes, atmospheric radiation processes, etc.), oceanic and sea ice spectra manifesting the necessary physical phenomena were integrated into the coupled model from among the foregoing elements as the essential components.

A global, high-resolution fully coupled model is indispensable to understand mechanisms of climate change how El Niño/Southern Oscillation is influenced in the progress of global warming, as well as, how these phenomena affect the climate in Japan.

Coupled Atmosphere–Ocean Model, CFES

Coupled atmosphere-ocean-sea ice model for the Earth Simulator (CFES) has been developed in Earth Simulator Center in collaboration with Frontier Research System for Global Change. AFES, which includes a simple surface model, coupled ocean-sea ice GCM (OIFES) which includes OFES and sea-ice component. In AFES, solar radiation process, cumulus clouds process, and wind effects are calculated under the fixed boundary condition obtained from OIFES. Heat flux, fresh water flux such as precipitation, river and sea-ice melting effects, and momentum flux such as wind stress are received by the ocean from the atmosphere. In the oceanic component, oceanic dynamics are calculated under the condition of forcing data which was given from the atmospheric component. After integration for a unit of time period, sea surface temperature is fed back to the atmosphere side as a boundary condition (Fig. 1).

Figure 1. Coupled atmosphere-ocean-sea ice model.

In CFES, original computational techniques have been applied. In order to fully utilize the parallelized computational power of the Earth Simulator, the execution of those components is achieved concurrently, and each model component is operated independently. In other words, by optimizing both the atmosphere and ocean models, the total computational efficiency of the coupled model is improved directly from point of view of decreasing computational cost.

Toward Climate Variation Research

Climate change projection that we are conducting involves test experiments for prediction of variability on climate time scale of several years to thousands of years. The El Niño/Southern Oscillation phenomenon, which is characterized by anomalously high sea surface temperature off shore of Peru, is the most important climate variability on the short-range time scale of a few months to several years. The predictability of the El Niño phenomena, indeed, the extent to which such prediction is even possible, is slated for verification. Climate change phenomena that occur on a scale of thousands of years include variability due to the thermohaline circulation driven by density contrasts. The possibility of predicting those climate change influenced by global warming also constitutes a direction of inquiry.

Additionally, reaching farther back in time, research will be conducted to represent climate variability in the paleoclimate by using simulations. What can be learned from the paleoclimate, which is climate change that took place on a time scale of tens of thousands of years in the past, might bring us suggestions to understand mechanisms of the climate change having progressed by present. Based on analysis of the chemical constituents of corals, marine sediments, and the ice cores obtained by boring glaciers and ice sheet, reconstruction of past climate can be made about the atmosphere and ocean conditions extending back tens of thousands of years. It enables us to verify the scale of changes during past glacial and warm periods in history.

Now, we are promoting to collaborate with domestic/foreign countries' researchers, in addition, we are planning to open to public the source code of CFES and results from experiments with CFES in near future.

Figure 2. Annual mean fields of the simulation results. (Left) Sea surface temperature.
(Center) Net heat flux. (Right) Net fresh water flux.