Mean circulation and variability in the global high-resolution GCM ― the Equatorial Currents System in the Pacific Ocean ―
Akio Ishida*1, Yuji Kashino*1, Humio Mitsudera*2 and Teruaki Kadokura*3
*1 Japan Marine Science and Technology Center
*2 International Pacific Research Center
*3 Fuji Research Institute Corp.
We have investigated the mean ocean circulation and the variability which are simulated by the JAMSTEC Eddy-resolving General Circulation Model (JEGCM). The model covers global domain except the Arctic Ocean with 1/4 degrees horizontal grid spacing and 55 vertical levels. The surface heat and freshwater flux is implemented as a restoring to the Levitus hydrographic data, and the Hellerman and Rosenstein wind stress is used to force the model. The model has been spun-up by the annual averaged climatologies in the first 2 years, and then forced by monthly averaged for 18 years.
The quasi-equilibrium state in the final years of the simulation shows many realistic features of ocean circulation including the separation and variability of western boundary currents especially of the Kuroshio, and the westward propagation of mesoscale eddies in the interior ocean. The model also well simulates the vertical structure of the equatorial currents system in the Pacific Ocean comprising the North and South Equatorial Currents, the Equatorial Undercurrent, the Subsurface Countercurrents (SSCCs), and the Equatorial Intermediate Current, which have not been well reproduced in previous high-resolution GCMs.
The model SSCCs have similar structures compared with the observed, i.e., (a) the SSCCs are associated with the pycnostat between 26.0 and 26.8 sigma, (b) deep and week in the west and shallow and strong in the east, (c) the densities in the SSCCs' cores show decreases to the east. The model North SSCC transports low salinity water in the intermediate layer in the North Pacific through the western boundary area. These results suggest the usefulness of this model for the studies of the general circulation in the equatorial Pacific and the interaction between the equatorial and subtropical ocean circulations.
Ocean Climate Change by Acoustic Tomography, Satellite Altimetry, and Modeling
Bruce M. Howe*1 and the ATOC Consortium
*1 Applied Physics Laboratory, University of Washington
Comparisons of gyre-scale acoustic and direct thermal measurements of heat content in the Pacific Ocean, satellite altimeter measurements of sea surface height, and results from a general circulation model show that only about half the seasonal and year-to-year changes in sea level is attributable to thermal expansion. Interpreting sea level climate change signals is therefore complicated. The annual cycle of heat flux is 150W / m2 peak-to-peak, corresponding to a 0.2 degreeC (vertically-averaged) temperature cycle; an interannual change of similar magnitude is also detected. Meteorological estimates of surface heat flux, if accurate, require a surprisingly large seasonal cycle in the advective flux.
