Figure 1: Predicted changes in carbon dynamics ofthe global terrestrial ecosystem in off-linesimulations with Sim-CYCLE. Simulations are basedon climate change scenarios obtained by threedifferent coupled general circulation models usingSRES emission scenarios.

Photosynthesis Plant biomass

Ecosystem respiration Soil carbon

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Person in Charge: T. Matsuno

a. Development of a Coupled Carbon Cycle- Climate Change Model

Terrestrial Carbon Cycle Model

Members: A. Itoh, K. Ichii, and K. Tanaka

This group develops a model that estimates carbonbudget of terrestrial ecosystem, which may exertshort- to long-term effects on atmospheric carbondioxide concentration. The model should allow us topredict leaf area index: an index of land-surfacefunctions with respect to atmosphere-biosphereexchange. In the FY2002, we have developed aframework of the ecosystem model, on the basis ofSim-CYCLE, which is a simple compartment modelincluding physiological responses to l ight,temperature, CO2, and water availability. The modelcould appropriately capture the observed state ofterrestrial carbon dynamics in various ecosystems,and then we applied the model to a preliminary off-line experiment to examine the responsiveness ofterrestrial carbon budget to global environmentalchange derived from the IPCC/SRES scenario. Theexperiment showed that terrestrial ecosystems wouldact as both positive and negative feedback mechanism,dependent on prescribed climate scenario, implyingan uncertainty of model prediction with the model(Figure 1). In the next fiscal year, we are planning tovalidate the model with a variety of observation data(e.g. satellite image and flux measurement) to reducethe uncertainty. Then, the model will be incorporatedinto the climate system model, allowing us to performon-line simulations including the interaction betweencarbon cycle and climatic dynamics.

(2) Subject 2: Development of Integrated Earth System Modelfor Global Warming Prediction

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b. Oceanic Biogeochemical Model

Members: M. Kawamiya, M. Aita, C. Yoshikawa, Y. Yamanaka, M. Kishi

This group is in charge of developing the oceancomponent of the integrated earth system model. Inthe first year of the project, an ecosystem model wasembedded in an ocean general circulation model andthe model results were compared with observationsafter integration of 7 years. The ecosystem model is asimple nitrogen-based one with 4 compartments, andthe circulation model is CCSR Ocean ComponentModel (COCO), which is cooperatively developed bythe CCSR, and FRSGC. Spatial and temporalvariations of the mixed layer depth, one of the mostimportant physical factors for pelagic ecosystems, arereproduced by the model including the largeamplitudes of seasonal variations in the northern

North Atlantic and the Southern Ocean. The modelresults are well compared to satellite observationsregarding surface chlorophyll distribution, in that theconcentrations are high in the areas with Ekmanupwelling such as northern North Atlantic, northernNorth Pacific, equatorial regions, and the SouthernOcean (Figure 2). The model also captures the distinctblooming event in the northern North Atlantic due tothe sudden shallowing of the mixed layer depth inspring. Incorporation of the carbonate system into themodel is also completed. Model integration of a fewthousand model years, required for achieving thestationary state, is going to be conducted. The modelhas a relatively fine resolution for a model for theglobal scale, and it is estimated that approximately 3months are needed even using the Earth Simulator tocarry out such a long integration, which means thatthe integration is virtually impossible with otherexisting supercomputers.

Figure 2: Seasonal variation of surface chlorophyllin the model. Units are mg/m3.

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c. Dynamical Global Vegetation Model

Members: T. Kohyama, H. Satoh

The objective of this group is to establish a plant-dynamics-model, which will be incorporated into theintegrated-terrestrial-model in Kyousei 2 project.This plant-dynamics-model is specifically designedfor predicting vegetation changes at high latitude ofthe Northern Hemisphere, where potentially large,rapid climate changes would occurs. Although mostof the present DGVMs assume that vegetationdynamics were regulated by gap mechanism,vegetation dynamics at high latitude would beprimarily regulated by climate and disturbanceregimes rather than gap mechanism. Accordingly, as

Figure 3: Time evolution of (a) tropospheric ozone inventory, (b) global mean methane, and (c)sulphate aerosol inventory simulated by the model using the SRES-A2 scenario. Solid lines representexperiments considering the effects of climatic changes, and dashed lines not considering.

d. Development of a Coupled StmosphericComposition - Climate Change Model

Model for Global warming - AtmosphericComposition Change Interaction

Members: M. Takigawa, S. Watanabe, T. Nagashima (NIES), K. Sudo, T. Takemura (Kyushu Univ.)

Ozone, a greenhouse gas as well as carbon dioxideand methane, is the most important chemical speciesfor tropospheric photochemistry to control the lifetimeof other chemical species. The principal objective ofour study is to evaluate the influence of troposphericand stratospheric ozone to the climate change by usinga photochemically coupled global circulation model.Additionally, our model will be used as a sub-component of the integrated model, and theinteraction with other sub-component such asvegetation and ocean chemistry will be considered.In this year, a new advection scheme was introducedinto the model. After 2-years integration, it is foundthat the new advection scheme improves the humidityin the upper troposphere. Next, the model, which isfully coupled with tropospheric photochemistry, isused for the simulation to evaluate impacts ofemission change and climate change independently(Figure 3). Global mean methane concentrationincreased to about 4ppmv in 2100 with emissionchange only, but to 3.3 ppmv with climate change,reflecting the impact of temperature and water vaporincreases on the methane lifetime (Figure 3 b).

e. Accurate Estimate of Feedbacks on theGlobal Warming through Interactions inthe Cloud - Aerosol - radiation System

Members: N. Kuba, T. Suzuki, T. Nozawa (NIES), Y. Tsushima, K. Suzuki, T. Nakajima

The purpose of our sub-group is to develop theparameterization for GCM to estimate the effect oftropospheric aerosol on the optical properties ofclouds i.e. the indirect radiative forcing of aerosol.

First, we investigated the parameterization to estimatethe indirect radiative forcing of aerosol in CCSR/NIES-GCM and ECHAM-GCM (Max Plank Institute).Second, we developed the parameterization toestimate the effect of CCN on the microstructure ofcloud (Kuba et al., 2003, Kuba and Iwabuchi, 2003).Third, we examined the treatment the output ofSpedral Radiation Transport Model for Aerozol(SPRINTARS; Takemura et al., 2000) to make thisparameterization effective.

The scale gap between cloud microphysical model andGCM is remarkable. To bridge this scale gap we areplanning to install the cloud microphysical model inNICAM and MRI/NPD-NHM (Saito and Kato, 1999).We conducted many numerical experiments using ourcloud microphysical model with particle method todevelop the parameterization to estimate therelationship between CCN and cloud microstructure.Due to the scale gap between microphysical modeland GCM, there are many problems to install this

a base of the vegetation-dynamics-model, we employAlaska Frame Based Ecosystem Code (ALFRESCO)that simulate vegetation change from arctic tundra toboreal forest in response to global changes in climate,fire, and land use. Although, ALFRESCO predictslandscape-level response of vegetation, it does notpredict changes in plant biomass nor forest size-structure, which will be required for the integrated-terrestrial-model. Thus, we extend ALFRESCO toincorporate plant growth model for predicting bothof the changes in plant biomass and forest size-structure. For finer simulation of vegetation change,we also explore to incorporate (1) seed dispersalprocess, (2) highly heterogeneous landscapes at borealand arctic areas.

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parameterization to GCM, such as how to estimatethe updraft velocity in the cloud from grid meanupdraft velocity, and how to estimate LWP of thecloud from the grid mean LWP. Therefore, we aretrying to compare the simulated results betweenGCM( grid scale is a few hundred km), NICAM (5km) coupled with cloud microphysical model withbase function expansion method and NHM (50 m)coupled with cloud microphysical model with binmethod.

f. Development of a Cryospheric ClimateSystem Model

Ice sheets are huge glaciers that extend over thecontinents. At present there are two ice sheets on theearth, the Antarctic ice sheet and the Greenland icesheet, which are together equivalent to more than 80meters sea level. Slight changes in the ice sheets havethe potential to affect the geography and economy ofthe worlds coastal regions. Therefore it is critical thatwe understand how much the ice sheets will changein size due to future changes, such as global warming.The aim of our research is to tackle these issues byusing coupled models of the ice sheets, the atmosphereand the seaice-oceans to simulate the evolution of thei c e s h e e t s . R u n s o n t h e E a r t h S i m u l a t o rsupercomputer are planned.

For the FY2002, the development and validation ofthe ice sheet model were done, since it has tosufficiently simulate the present situation. Sensitivityof the ice sheet model to the regional warming wasinvestigated and it is found that a 3 to 4 degree Celsuiswarming is sufficient for the Greenland ice sheet tohalf its volume or raise the sea level by 3 meters,although the response time is about the order ofhundreds to thousands years. For the futureprediction, not only the ice sheet model but also theclimate model (GCM) should predict the regionalclimate changes over the Antarctic and Greenland icesheet region with both high resolution and highprecision, since ice sheet is very sensitive to a smalltemperature change. The evaluation of theatmospheric GCM is done in a high resolution (T106,1 deg. lat. and lon.) AGCM, which was done so faronly by one GCM (ECHAM) referred in the IPCCThird Assessment Report. It is concluded that carefultreatment of the albedo of the snow over the ice sheetand the altitude correction could bring about a morerealistic result. Moreover, one way coupling of highresolution GCM to Ice sheet model was attempted.The role of ice sheet flow becomes important after 21century and lasts for millennium. Since this onewaycoupling does not include the detailed scenario ofwarming and the albedo feedback effect, the fullycoupled ice sheet - GCM is essential for the next step.

To investigate the other important cryospherecomponent, sea ice, in the coupled GCM, we focusedon the sea ice dynamics and assess its effect on thepresent-day sea ice climatology. Previous studiesusing numerical models have shown that summer seaice area in the Southern Ocean decreases due to thesea ice dynamics. In winter, on the other hand, sea icedynamics cause little difference in the simulated seaice area. However, one of the reasons for this lesssensitivity in winter may be that dynamic responseof the ocean, such as convection, has not beenincorporated in the sea ice models used in theexperiments. In the present study, therefore, weemploy a coupled ocean-atmosphere GCM (OAGCM)to verify whether sea ice dynamics can affect sea icedistribution by controlling the ocean convectionprocess. It is found that (a) sea ice dynamics increasethe static stability of the ocean by enhancingfreshwater release near the ice edge, and (b) sea icedynamics increase the static stability by decreasingthe sea ice concentration and thickness, whichenhances the deep water cooling in winter (especiallynear the Antarctic continent). In the NorthernHemisphere, on the other hand, impact of sea icedynamics on the sea ice extent appears to be minor,although significant effect on sea ice thickness wasfound.

Figure 4: Difference in surface fresh water fluxaround the Antarctica in August betweenexperiments with and without sea ice dynamics.Positive values mean that those with dynamics arelarger than without (positive upward). Yellow solidand dashed lines show the edges in the experiments

with and without dynamics, respectively.

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d. Improvement of the Physical ClimateSystem Model

Members: S. Watanabe, S. Emori, Ts. Suzuki,Ta. Suzuki, K. Takata, M. Kimoto (Univ. ofTokyo), T. Matsuno, H. Hasumi (Univ. ofTokyo)

Main objective of this sub-group is to improve aclimate model (CCSR/NIES model) which consists ofa coupled atmosphere and ocean GCM, a sea icemodel, and a land surface model. In particular, variousimportant processes in the stratosphere will beimproved and/or newly implemented.

Effects of anthropogenic gases and aerosols on theozone chemistry may cause dramatic climatevariability over the whole atmosphere throughcomplex interactions between radiative anddynamical processes. In addition, variability of thesolar radiation can cause ozone changes and climatevariability in the middle atmosphere, which maycoupled with climate change near the surface. Hence,numerical studies should be conducted with animproved version of the climate model.

Behaviors of internal gravity waves and thoseinfluences on the general circulation should beinvestigated by performing numerical experimentswith an ultra-high resolution GCM, since they playvery important roles in the middle atmosphere.

In this year, vertical domain of the atmosphere GCMwas extended to the mesopause level (~80 km).Importance of various atmospheric waves controllingmean states and variability of the middle atmospherewas confirmed by a series of numerical experiments.For this purpose, hundreds of sets of horizontal-and-vertical resolution and physical parameters of themodel were tested. Simultaneously, numericalresources of the Earth Simulator required for thesesimulations were checked. The highest resolutionsimulation performed to date is T106 L250, i.e., 1.1degrees in both longitude and latitude and 300 m invertical.

Sigma vertical coordinate system used in the originalGCM was replaced with a sigma-pressure hybridcoordinate. As a result, accuracy of transport processesin the stratosphere was improved. On the other hand,causal mechanisms of cold and moist biases near thetropopause were investigated, though yet to be solved.

Figure 5: Mixing ratio of water vapor on 120 hPa in January, averaged over the 20th-24th model yearsusing the identical initial and boundary conditions with (a) the sigma-p hybrid coordinate and (b)the sigma coordinate.