Updated: August 11, 2010

About Geophysical Fluid Simulation Research Group

The Geophysical Fluid Simulation Research Group conducts high-resolution and large-scale simulations of the ocean and atmosphere to understand the oceanic roles in global climate and its variability.

The “virtual” ocean and atmosphere in the Earth Simulator

Figure 1

Figure 1: Monthly-mean fields in February of the 19th year from a global simulation using coupled atmosphere–ocean model, CFES. (From top to bottom) wind speed at 250-hPa height, precipitation, sea surface temperature, and current speed at 1500-m depth. [Click to enlarge the figures.]

A set of computer programs describing equations which govern large-scale variability of the ocean and atmosphere based on fluid dynamics and thermodynamics is called “general circulation model” (GCM). Our group develops and improves OFES (oceanic GCM), AFES (atmospheric GCM), and CFES (coupled atmosphere–ocean GCM), which are massively parallelized and optimized for the Earth Simulator, and conducts simulation studies utilizing these models under a collaboration with Research Institute for Global Change of JAMSTEC and other institutes in the world.

Operational and research institutions worldwide including JAMSTEC conduct observations day and night in order to monitor the state of the ocean and atmosphere and to study their mechanisms. Small and fast phenomena, however, cannot be captured by the current observing systems. Moreover, some quantities are difficult to measure. Global high-resolution models, or the “virtual” ocean and atmosphere on the Earth Simulator, are adequate tools in understanding the mechanisms by obtaining information missing in the observations. For example, eddy-resolving quasi-global ocean simulation at 10-km mesh for over a past half centuries produced with OFES are used by researchers world-wide as a substitute of the real ocean complementary to observations. “Virtual” ocean and atmosphere enable us to conduct numerical experiments with various conditions to disentangle the complexity of the climate system.

Resolving small eddies and filaments in the Kuroshio Current

Figure 2

Figure 2: Surface relative vorticity (× 10-5 s-1) [Click to enlarge the figures.]

Recent satellite observations revealed even smaller eddies and filaments of only a few km in size in mesoscale eddies (about 100 km). It is suspected that these submesoscale structures influence ocean surface fields. In order to clarify the effects of the submesoscale phenomena, super high resolution experiments in the Northern Pacific are being conducted using a 3-km mesh ocean general circulation model (OFES). Submesoscale eddies and filaments are successfully resolved along the Kuroshio Current and Tsushima Warm Current (Fig. 2).

Rising heat from the Gulf Stream

Figure 3

Figure 3: Annual mean atmospheric vertical velocity and ocean current speed. [Click to enlarge the figures.]

It has been revealed that heat from the Gulf Stream warms the air in the mid-latitudes to cause significant updraft by recent satellite observations and simulations using AFES. Figure 3 is a three dimensional visualization of atmosphere–ocean interactions along the Gulf Stream in a high resolution (atmosphere 50 km, ocean 25 km) simulation using CFES. Above the Gulf Stream, which reaches a depth of 1,000 m, along the western boundary of the North Atlantic, the associated updraft climbs to roughly 10,000 m from the sea surface in this simulation.