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JAMSTEC 2002 Annual Report Frontier Research System for Global Change P (mb) 0.1 1 10 1E+2 1E+3 0.0 5.0 10.0 15.0 20.0 25.0 Heating Rate (K/d) P (mb) 0.1 1 10 1E+2 1E+3 a TRO -0.2 0.2 -0.4 0.0 0.4 Error (K/d) 0.0 10.0 20.0 30.0 Heating Rate (K/d) P (mb) 0.1 1 10 1E+2 1E+3 c e MLW SAW CKD LBL Error CKD LBL Error CKD LBL Error -0.2 0.2 -0.4 0.0 0.4 Error (K/d) 0.0 5.0 10.0 15.0 20.0 25.0 Heating Rate (K/d) P (mb) 0.1 1 10 1E+2 1E+3 0.1 1 10 1E+2 1E+3 b MLS 0.0 5.0 10.0 15.0 20.0 25.0 Heating Rate (K/d) P (mb) 0.1 1 10 1E+2 d SAS -0.2 0.2 -0.4 0.0 0.4 Error (K/d) 0.0 5.0 10.0 15.0 20.0 25.0 Heating Rate (K/d) P (mb) f USS CKD LBL Error CKD LBL Error CKD LBL Error -0.2 0.2 -0.4 0.0 0.4 Error (K/d) 1E+3 0.0 10.0 20.0 30.0 Heating Rate (K/d) to Baiu. As to the effect on the intra-seasonal (M-J) oscillation, the inclusion of the trigger apparently improves its generation and propagation. (iii) Improvement in the diagnosis of cloud amount So far there was a problem regarding the determination of cloud amount in the currently used CCSR/NIES AGCM. Namely, in increasing the vertical resolution hence increasing the number of cloud layers the simulated total cloud amount tends to be larger compared with the observation though the TOA radiation balance is correct (parameters are tuned to keep the balance). The most likely cause of the problem was considered to come from more and more "thin clouds" formation with the increase of layers. So, in counting cloud amount or identifying cloud area, a threshold in cloud optical thickness was introduced. The value is . in accord with the threshold adopted by ISCCP. Results of simulation with this threshold were apparently better than those without it. -0.2 0.2 -0.4 0.0 0.4 Error (K/d) -0.2 0.2 -0.4 0.0 0.4 Error (K/d) Fig.19 Spectrally integrated longwave heating rates calculated by ck-D model, LBL model and differences between them for six atmospheres (a, b, c, d, e and f). and . For long wave the new scheme has such an accuracy that heating/cooling rate errors are less than . K/day in the entire troposphere and . K/day above the tropopause. At short wave range the error in heating rate is less than . K/day in the troposphere and less than . K/day above the tropopause. (ii) Introduction of "trigger" into the convection parameterization Since most of cumulonimbus type convection occurs under the latent instability conditions, there must be some triggering mechanism to bring an air-parcel up to the level of free convection by overcoming the negative buoyancy. So, we have introduced a trigger process to the CCSR/NIES AGCM and tested its performance. The introduction of the trigger intensifies the ITCZ and also enhances the precipitation belt corresponding a-. AGCM Simulation of Synoptic- and Meso-scale Weather Systems Recent progress of AGCM enables us to make simulation studies of various circulation systems. However, the previous studies mainly discussed the features of circulation systems in seasonal or monthly averaged fields, without special interest in individual weather systems, such as the extratropical cyclone, polar front, polar low and Meiyu-front. AGCM studies of each weather system are needed to understand the actual climate variations. We therefore focus our attention on these weather systems simulated in the AGCM. In , we mainly analyzed the results of simulation by seasonally varying climatological SST run by TL. The result for June and July indicates quasiperiodic alternation of "Baiu phase" and "non-Baiu phase". In the "Baiu phase", the large-scale circulation systems, such as the upper cold lows and blocking ridge in the northern latitudes, and westward extending Pacific subtropical anticyclone, monsoon westerly and 136
Japan Marine Science and Technology Center Frontier Research System for Global Change subtropical jet stream are properly maintained. Only under this large-scale condition, the realistic Baiu frontal precipitation zone is formed in the model. The simulation for January indicates the reasonable quasi-periodic development of extratropical cyclones over the east coast of the Asian continent and associated polar air outbreak. A typical polar low is formed over the coastal sea area ~km west of the major extratropical cyclone that developed over the Northwestern Pacific Ocean, under the influence of a short wave trough. The strong heating due to the energy supply from the sea surface contributes to the genesis of the polar low through decreasing the vertical stability and sustaining the thermal gradient. Takeshi Enomoto primarily investigated the summer climate in east Asia using observed data and model output. He extended his research on the Ogasawara (Bonin) anticyclone that appears in late summer over Japan to study its interannual variability. He confirmed a robust relation between the undulation of the subtropical jet and intensification of the high in its inter annual variability using NCEP Reanalysis, which is consistent with his previous numerical work. In association with researchers in other program at FRSGC and the Earth Simulator Center, he also performed a -km mesh global simulation of the Baiu/Meiyu frontal zone using AFES (AGCM code for the Earth Simulator) of the CCSR/NIES model. b. Next-generation Model Development b-. Next generation Atmospheric Modeling A new high resolution atmospheric general circulation model referred to as NICAM (Nonhydrostatic ICosahedral Atmospheric Model) is being developed. It is a grid model with an icosahedral structure and is based on the non-hydrostatic equations. The main target is high-resolution climate simulations by improving representation of cumulus convection with higher resolutions. This project started in and to date a dynamical core of the global model has been developed. We are running the new model on the Earth Simulator and found that the computational efficiency of NICAM is superior to that of a well-tuned spectral transformation model at high resolutions with a grid size smaller than km. As a subset of NICAM, we are also developing a regional Cartesian non-hydrostatic model. The model structure is almost parallel to the global icosahedral model, so that new dynamical and physical schemes are tested in order to be installed to the global model. Both models are based on the newly considered flux form Eulerian scheme, which guarantees conservation of mass and total energy. We are introducing physical processes to the regional model and tesing their performances. We are also performing radiative-convective equilibrium experiments to study interaction between clouds and radiation. We have performed the standard experiments proposed by Held and Suarez () and compared the results with those obtained with the CCSR/NIES spectral model adapted to the Earth Simulator, called AFES (Shingu et al., ). Both models are run as the dynamical cores, i.e. no physics are included. We found that the result of NICAM is almost comparable to that of AFES at the resolution glevel (∆x km) for NICAM and T for AFES. Figure compares the computational time required for one time step integration using the Earth Simulator. We use nodes where each node has processors and the corresponding peak performance is T Flops. The abscissa is the maximum total wave number N of the triangular truncation in spectral model or the minimum horizontal wavelnegth λ min corresponding to N. Figure shows that while the curve for AFES approaches asymptotically to the line N , the curve for NICAM approaches the line N as resolution becomes higher. If we interpret the resolution of NICAM as λ min = ∆x, this shows that NICAM is almost one-order magnitude efficient in comparison to AFES for all the resolutions. Even if the resolution of NICAM is interpreted as λ min = ∆x, the efficiency of NICAM becomes superior to AFES at higher resolu- 137
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