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JAMSTEC 2002 Annual Report Frontier Research System for Global Change RMS of SSH anomaly (year 46-50) 70N 60N 50N 40N 30N 20N 10N EQ 10S 20S 30S 40S 50S 60S 70S 60E 120E 180 120W 60W 3 6 9 12 15 18 21 24 27 30 Fig. 2 Distribution of the standard deviation of sea-surface height anomalies simulated in the OFES with 0.1˚ resolution. Large variability associated with strong eddy activity along the western boundary currents and the Antarctic Circumpolar Current is realistic as compared with satellite altimetry data. b. Climate Diagnostics Group b-. Climate Variability in the Extratropical Atmosphere We have extended our analysis to multidecadal modulation in the occurrence of an inter-annual seesaw (AIS) between the intensities of the Aleutian and Icelandic lows. We found that the occurrence of AIS was much less frequent in the s and s than since the s. The following two factors are likely to cause this bi-decadal modulation: (i) a recent midwinter tendency toward a stronger meander of the westerlies over North America that allowed Rossby wave activity to be transferred effectively into the North Atlantic from the North Pacific; and (ii) another midwinter tendency towards more zonally-elongated and more persistent anomalies developing over the North Pacific. We also found that model-simulated AIS exhibits a multidecadal modulation in each of the AFES (AGCM for the ES) and ECHAM at IRI without any SST anomalies imposed, suggesting the importance of internal dynamics of the atmospheric flow in causing the long-term AIS modulation. b-. Climate Variability in the Extratropical Coupled Atmosphere-Ocean System Linearizing our high-resolution data of turbulent heat flux anomalies with respect to anomalies in SST, air temperature and surface wind speed, we found that warm (cool) SST anomalies along the Pacific subarctic front associated with the decadal variability inherent to the North Pacific accompany the enhanced (suppressed) heat release into the atmosphere (Fig. ). This is important evidence that, unlike in other locations in the extratropics, SST anomalies in the subarctic frontal zone can force the atmosphere. This is likely through systematic changes in the storm track activity, reinforcing stationary atmospheric anomalies over the Pacific. b-. Collaboration with the ESC As our continuous contribution to super-high resolution simulations of the global atmosphere with the AFES, we analyzed its -day integration with T resolution and vertical levels under the climatological SST forcing. We have found that AFES can realistically simulate synoptic weather systems and their internal structure. The model can realistically simulate a polar low over the Sea of Japan with mesoscale precipitation bands. Organization of shallow convective clouds along cold surface winds and topographic precipitation behind those cyclones was also simulated in a realistically-looking manner. c. Predictability Research Group To deepen our understanding of the physical nature of our climate system, basic studies have been performed on the thermodynamical properties of turbulent fluid systems. Each of the mean states of the systems is shown to correspond to a unique state in which the entropy production rate by thermal and viscous (turbulent) dissipation is maximized. An application of a new method of entropy evaluation to large-scale ocean circulation models has revealed that the oceanic deep-water circulation, when perturbed, tends to change its state from the one with a lower rate of entropy production to the other with a higher rate. These results suggest that the dissipation rate of available potential energy may be used as a measure of the entropy production rate for representing the relative stability of nonlinear fluid systems. 120
Japan Marine Science and Technology Center Frontier Research System for Global Change Dec-Jan Feb-Mar 60N 50N (a) Qe 60N 50N (b) Qe 40N 40N 30N 30N 20N 120E 150E 180 150W 120W 20N 120E 150E 180 150W 120W 60N 50N (c) w(qs') 60N 50N (d) w(qs') 40N 40N 30N 30N 20N 120E 150E 180 150W 120W 20N 120E 150E 180 150W 120W 60N 50N (e) -w (qa') 60N 50N (f) -w (qa') 40N 40N 30N 30N 20N 120E 150E 180 150W 120W 20N 120E 150E 180 150W 120W 60N 50N (g) w'(dq) 60N 50N (h) w'(dq) 40N 40N 30N 30N 20N 120E 150E 180 150W 120W 20N 120E 150E 180 150W 120W -40 -30 -20 -10 0 10 20 30 40 Fig. 3 (a-b) Difference maps of bi-monthly anomalies in upward latent heat flux (W/m 2 ) between the opposing phases of the dominant mode of the North Pacific decadal variability for (a) November- December and (b) January-February. (c-d); As in (a-b), respectively, but for a contribution from SST anomalies. (e-f); As in (a-b), respectively, but for a contribution from air temperature anomalies. (g-h); As in (a-b), respectively, but for a contribution from wind speed anomalies. 2. Hydrological Cycle Research Program Asian countries depend, to a great extent, on summer and winter monsoon precipitation for their water resources. The regional as well as continental-scale hydrological cycles, at the same time, affect variabilities of monsoon climate through various feedbacks. To understand the physical processes involved in the hydrological cycles is, therefore, very crucial for predicting the hydro-climate condition with various time-scales. This program will focus on understanding the hydrological processes in the weather and climate systems, and develop models for predicting regional and continental-scale hydrological cycles. Particular emphasis will be put on the processes in the Asia/Australia monsoon region and the Eurasian continent. a. Group for Large-scale Hydrological Processes This group focuses on the impact of climate change and variability on continental and regional scale hydrological cycle and their feedbacks to climate variability, based on global scale reanalysis data, satelliteremote sensing data and in-situ measurement data. Validation of hydrological processes obtained from simulations by General Circulation Models (GCM) and regional climate models is also carried out by using observational data mentioned above. In the FY, the following studies were conducted. a-. Variations of Global, Continental, and Regionalscale Energy and Water Cycle Long-term trends in the energy and hydrological cycle in the tropics were examined using global gridded precipitation data (CMAP, GPCP), Outgoing Longwave Radiation (OLR) data as a convective activity, diabatic heating data from NCEP- reanalysis and divergent circulation parameters for the recent two decades (-). The results demonstrated a decrease of precipitation (weakening of convective 121
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