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JAMSTEC 2002 Annual Report Frontier Research System for Global Change Our dataset shows good consistency with previous knowledge on the ocean state. As for water masses, North Pacific Intermediate Water (NPIW), Subtropical Mode Water, and South/North Pacific Tropical Water, which characterize subsurface water mass structure in the North Pacific, are well reproduced. In order to validate the net air-sea heat flux field in the North Pacific, we compared our result with recent products derived from the satellite data (J-OFURO, Kubota et al., ). Since the satellite products are only one-year measurement, the quantitative difference between the two mainly comes from large interannual variabilities. Nevertheless, its overall patterns/intensities in the midlatitude region (˚N(S)-˚N(S)) have good similarities (.Wm rmsd) with the observation. Further, we have compared our results with those obtained by the nudging method often used. As a result the NPIW is reproduced largely by the artificial supply of less saline water in the nudging case (not shown), which prevents us from investigating its formation and transformation processes. In contrast, it is not the case in our reanalysis dataset because artificial sources or sinks for temperature and salinity are never added in our D-VAR system. We have also performed a sensitivity experiment. This is the powerful advantage that facilitates the identification of the water mass pathway. The experiment reveals that the origin of NPIW can be traced back to the Okhotsk Sea and the Bering Sea in the subarctic region and to the subtropical Kuroshio region further south (Fig.). These results are in broad agreement with recent studies (e.g., Yasuda et al. ). d-. Preliminary Results of s Ocean Reanalysis Using the assimilation method described above, we have initiated a long-term ocean reanalysis experiment. The aims are to get a dynamically consistent ocean state in the s and to investigate the origin and the propagation of interannual phenomena like El Niño. The assimilation method is the D-VAR with preconditioned CG, using the ocean model MOM and its adjoint code. The period is from January to December , and a spinup is performed from to . Taking account of the typical time scales of interannual phenomena, assimilation windows are set to . years. We have already performed the preliminary experiment to check the ability of our method. adS*dS sens_1nn2 -01yrs -0 / 4 sigma 26.8 adS*dS sens_1nn2 -05yrs -0 / 4 sigma 26.8 65N 65N 60N 60N 55N 55N 50N 50N 45N 45N 40N 40N 35N 35N 30N 30N 25N 25N 20N 20N 15N 15N 10N 10N 5N 110E 120E 130E 140E 150E 160E 170E 180 170W 160W 150W 140W 130W 120W 110W -5e-05-4.5e-05-4e-05-3.5e-05-3e-05-2.5e-05-2e-05-1.5e-05-1e-05 -5e-06 -5e-05-4.5e-05-4e-05-3.5e-05-3e-05-2.5e-05-2e-05-1.5e-05-1e-05 -5e-06 adS*dS sens_1nn2 -03yrs -0 / 4 sigma 26.8 adS*dS sens_1nn2 -06yrs -0 / 4 sigma 26.8 65N 65N 60N 60N 55N 55N 50N 50N 45N 45N 40N 40N 35N 35N 30N 30N 25N 25N 20N 20N 15N 15N 10N 10N 5N 110E 120E 130E 140E 150E 160E 170E 180 170W 160W 150W 140W 130W 120W 110W 5N 110E 120E 130E 140E 150E 160E 170E 180 170W 160W 150W 140W 130W 120W 110W 5N 110E 120E 130E 140E 150E 160E 170E 180 170W 160W 150W 140W 130W 120W 110W -5e-05-4.5e-05-4e-05-3.5e-05-3e-05-2.5e-05-2e-05-1.5e-05-1e-05 -5e-06 -5e-05-4.5e-05-4e-05-3.5e-05-3e-05-2.5e-05-2e-05-1.5e-05-1e-05 -5e-06 Fig.22 Product of adjoint variable of S by its increment dS on 26.8 sigma in the case of 'artificial cost' input at 43N, 180E (400m-depth) with streamline on the same isopycnal surface; 1-year, 3-year, 5-year, and 6-year backward calculation. 140
Japan Marine Science and Technology Center Frontier Research System for Global Change d-. Development of Assimilation Scheme Using Statistical Method The analysis scheme for the Ensemble Kalman Filter has been implemented using MPI fortran on the Compaq Alpha SC. The system has been tested on the Compaq Alpha SC with an ensemble size of members, assimilating a range of real data. The analysis code has been successfully tested on the Earth Simulator. A further issue under investigation is the use of a range of parameter values across the ensemble members. This is intended to address the question of model error, since using (incorrectly specified) fixed parameter values contributes to structural model error. Some preliminary experiments have been undertaken in collaboration with the Paleoclimate Group of the Global Warming Research Program using a low-resolution climate model in identical twin tests. 7. International Pacific Research Center (IPRC) Since FRSGC's IPRC Program is fully integrated into the research at the IPRC, the IPRC research efforts and results for FY are briefly summarized below. For more detailed information visit the IPRC website, http://iprc.soest.hawaii.edu, which posts the IPRC annual reports and issues of the IPRC Climate, IPRC's semiannual newsletter. Science Plan The work of the IPRC scientists is guided by the IPRC Science Plan, which is reviewed annually and updated to reflect developments. The newest version, Version ., is posted on the IPRC website. The plan consists of the following four scientific themes: Theme : Indo-Pacific Ocean Climate Theme : Regional Ocean Influences Theme : Asian-Australian Monsoon System Theme : Impacts of Global Environmental Change Each theme has a Goal, which broadly outlines the theme's subject matter and specific Objectives, which are achievable within a finite amount of time and with well-defined resources. It is expected that these four themes will endure throughout the IPRC lifetime, but additional themes may be added at some future time. The objectives, on the other hand will change with research developments. The IPRC research strategy is to carry out diagnostic analyses and modeling studies of the atmosphere, ocean, and coupled ocean-atmosphere-land system, rather than to conduct experimental programs. Research on FY a. Theme : Indo-Pacific Ocean Climate Regarding Pacific Ocean circulation and climate, research included modeling studies of the Kuroshio Extension, the California Current, and the low-latitude western boundary currents, as well as studies of inertial instability of the equatorial undercurrent. Regional atmospheric models, including the IPRC Regional Climate Model, were applied to the study of the Kuroshio, the East China Sea, and eastern tropical Pacific climate–particularly the effects of the Andes. Atmospheric and coupled GCMs were used to study the effect of continental asymmetry on the northward-displaced ITCZ and the influence of SST anomalies on extratropical storm tracks. Regarding the Indian Ocean, studies were conducted on the relationship between the Indian Ocean Dipole and the El Niño-Southern Oscillation; the remote climate effects of Indian Dipole events; the effects of the monsoons, El Niño, La Niña, and the Indian Ocean Dipole on Indian Ocean circulation by using salinity tracers in a .-layer ocean model; and the relative strength of the fall and spring Wyrtki Jets by analyzing data products and comparing them with ship-drift data. Application of satellite observations to climate research has emerged as a new strength of Theme- research and has led to the discovery of SST effects on local winds: From the equator to mid-latitudes, results show a robust and ubiquitous pattern of ocean-toatmosphere feedback, namely, surface wind speeds 141
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