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1997 Vol. 14, No. 4

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A Land Surface Model (IAP94) for Climate Studies Part I: Formulation and Validation in Off-line Experiments
Dai Yongjiu, Zeng Qingcun
1997, 14(4): 433-460. doi: 10.1007/s00376-997-0063-4
The IAP (Institute of Atmospheric Physics) land-surface model (IAP94) is described. This model is a compre-hensive one with detailed description for the processes of vegetation, snow and soil. Particular attention has been paid to the cases with three water phases in the surface media. On the basis of the mixture theory and the theory of fluid dynamics of porous media, the system of universal conservational equations for water and heat of soil, snow and vegetation canopy has been constructed. On this background, all important factors that may affect the water and heat balance in media can be considered naturally, and each factor and term possess distinct physical meaning. In the computation of water content and temperature, the water phase change and the heat transportation by water flow are taken into account. Moreover, particular attention has been given to the water vapor diffusion in soil for arid or semi-arid cases, and snow compaction. In the treatment of surface turbulent fluxes, the difference between aerodynamic and thermal roughness is taken into account. The aerodynamic roughness of vegetation is calculated as a function of canopy density, height and zero-plane displace?ment. An extrapolation of log-linear and exponential relationship is used when calculating the wind profile within canopy. The model has been validated against field measurements in off-line simulations. The desirable model’s per?formance leads to the conclusion that the IAP94 is able to reproduce the main physical mechanisms governing the en?ergy and water balances in the global land surface. Part II of the present study will concern the validation in a 3-D experiment coupled with the IAP Two-Level AGCM.
Simulation of East Asian Summer Monsoon with IAP CGCM
Chen Qiying, Yu Yongqiang, Guo Yufu
1997, 14(4): 461-472. doi: 10.1007/s00376-997-0064-3
East Asian summer monsoon simulated by a coupled ocean-atmosphere general circulation model developed in the Institute of Atmospheric Physics (IAP CGCM) is analyzed. The precipitation, low-level streamline field, sea level pressure, low-level temperature and mixing ratio are compared with the observed ones respectively. The results show that IAP CGCM can simulate most features of summer monsoon circulation, but it still has some important systematic errors. The simulated Somali jet tends to be much weak and lies too far south. The cross-equatorial flows between 120oE and dateline are also too weaker in the model than those in reality, while the South Asia monsoon low is stronger than that in the observation and reaches, further east. At the same time, the subtropical high in the western Pacific extends too far west and north. Accompanied by these deviations in tropical and subtropical zones, the westerly troughs in the middle and high latitudes affect further southerly regions in China than those observed. All these deficiencies in simulating summer monsoon circulation result in the errors in modelled precipitation in East Asia, which include the underestimation of precipitation over East Asia in summer, the prema?ture emergence of maximum precipitation and the further southerly rainfall belt in East Asia than the observed one. So the most obvious drawbeck of the model is the apparent underestimation of Meiyu frontal rainfall.
Nonlinear Retrieval of Atmospheric Ozone Profile from Solar Backscatter Ultraviolet Measurements: Theory and Simulation
Li Jun, Lu Daren
1997, 14(4): 473-480. doi: 10.1007/s00376-997-0065-2
The Solar Backscatter Ultraviolet and Total Ozone Mapping Spectrometer (SBUV/TOMS) instrument has provided useful data for deducing ozone vertical profiles and total ozone amounts. Although, data processing tech-niques for solving the inverse problem have been discussed, the retrieval accuracy still needs to be improved by devel-oping new methodology. In this paper the Newtonian non-linear iteration method was applied to the Ultraviolet radiative transfer equation to retrieve the atmospheric ozone vertical distribution. In order to reduce the number of unknowns for retrieval and make the solution procedure more stable, the atmospheric ozone profile is represented by its Empirical Orthogonal Functions (EOFs) which can be derived from a set of global ozone profiles such as TIGR. Ozone retrievals based on simulated SBUV albedo measurements from 6 model atmospheres show the potential ap-plication of this method in operational processing of SBUV real observed measurements which will fly on the satellite such as NOAA-K.
Ozone Vertical Profile Characteristics over Qinghai Plateau Measured by Electrochemical Concentration Cell Ozonesondes
Liu Qijun, Zheng Xiangdong, Luo Chao, Ding Guoan, Li Xingsheng, Zhou Xiuji
1997, 14(4): 481-490. doi: 10.1007/s00376-997-0066-1
An analysis of 50 ozonesondings in Xining (36.43oN, 101.45oE , 2296m, ASL), between April 1995 and August 1996 is presented. General vertical distribution characteristics and seasonal changing of ozone profile are reported. The analysis indi?cates that the stratospheric ozone concentrations of Autumn and Summer are lower than those of Spring and Winter; and the highest value of the tropospheric ozone concentrations is found in Summer; ozone concentration changing is bigger from the troposphere to the lower stratosphere altitude region, while it is stable in the middle and upper stratosphere region; there is a lower ozone concentration region in 10-15 km altitude; the result why higher ozone concentration of the troposphere occurs in Summer is the ozone injecting from the middle and upper stratosphere.
The Influence of Tibetan Plateau on the Interannual Variability of Asian Monsoon
Wu Aiming, Ni Yunqi
1997, 14(4): 491-504. doi: 10.1007/s00376-997-0067-0
Forced by the realistic SST, an atmospheric general circulation model (AGCM) with 9 sigma levels in vertical and rhomboidal truncation at wave number 15 in the horizontal is run for 16 years with and without the Tibetan Pla-teau respectively (called TP and NTP experiment). The result simulated is used to investigate the influence of the Tibetan Plateau on the interannual variability of Asian monsoon. It is found that the interannual variability of Asian monsoon associated with El Nino / La Nina in NTP experiment is quite different from that in TP experiment. With the Tibetan Plateau included, the results are consistent with the observation very well. To a great extent, the anoma-lous variation of Asian monsoon during El Nino / La Nina period in observation is due to the existence of the Tibetan Plateau. Therefore, the topography of the Tibetan Plateau is an important factor to the interannual variabili-ty of Asian monsoon.
Vertical Ozone Profile over Tibet Using Sage I and II Data
Zou Han, Gao Yongqi
1997, 14(4): 505-512. doi: 10.1007/s00376-997-0068-z
This paper discusses the vertical ozone distribution over Tibet using SAGE I and SAGE II data. The annual and seasonal vertical ozone profiles in 10.5-50.5 km a.s.l. over Tibet are analyzed to understand the vertical structure of low ozone value in this region, Regarding to the local ozone deficit, these profiles are compared with the vertical ozone distribution in the non-mountain areas at the same latitudes. The summer low ozone and the May maximum ozone deficit are detected from the SAGE data. The largest ozone deficit in May is found in 15.5-20.5 km a.s.l. centered at 16.5 km over this region. This ozone deficit can be related to the upward mass transfer described by poten-tial temperature variation over Tibet.
Simulation of East Asian Summer Monsoon by Using an Improved AGCM
Lin Zhaohui, Zeng Qingcun
1997, 14(4): 513-526. doi: 10.1007/s00376-997-0069-y
The IAP 2-L AGCM is modified by introducing a set of climatological surface albedo data into the model for substituting the model’s original surface albedo parameterization. The comparison between the observations and the simulation results by the modified model shows that the general features of the East Asian summer monsoon can be well reproduced by the modified IAP 2-L AGCM. Especially for the simulation of monsoon precipitation, the modi-fied model can well reproduce not only the monthly mean features of the summer monsoon rainfall over East Asia, but also the stepwise advance and retreat of the East Asian summer monsoon rainbelt. Analysis results demonstrate that the good simulation of the monsoon rainfall is closely related to the reasonable simulation of the large scale gen-eral circulation over East Asian region, such as the western Pacific subtropical high, Asian monsoon low and the low level flows. The good performance of the modified model in the rainfall simulation shows its great potential to serve as a useful tool for the prediction of summer drought / flood events over East Asia.
Symmetric Development of Meso Perturbation in Zonally Curved Basic Flow
Zhou Weican, Chen Jiukang, Zhou Shunwu
1997, 14(4): 527-534. doi: 10.1007/s00376-997-0070-5
Addressed is a problem as to meso perturbation wave ensemble development in a curved basic flow in the contest of a f-plane non-hydrostatic equilibrium acoustic wave filtering model in natural coordinates with the aid of the WKJB and energetic approaches. Results show that the symmetric development depends crucially on the matching of structures of the disturbance wave and background field, and for a smooth (curved) basic flow the wave ensemble evolution hinges upon the spatial imhomogeneity of nonthermal wind of the background field (under nongradient wind balance). Finally, presented is the wave ensemble evolution in relation to the thermal curvature vorticity in the background field.
The Effect of Mesoscale Flows on Regional Atmospheric Transport in a Complex Terrain
Jia Xinyuan
1997, 14(4): 535-540. doi: 10.1007/s00376-997-0071-4
Model results simulated over a complex terrain under a synoptically calm condition, using a three-dimensional (3-D) regional-scale meteorological acid deposition model (RMADM), show that thermally induced mesoscale cir-culations (MCs): sea-and land-breeze circulations and up- and down-slope flow circulations play a fundamental role in determining how the pollutants being dispersed. Analysis showed that under synoptically calm condition, the role played by the MC would dilute the smoke released during the early stage of the emission, the accumulation, however, would become important if the synoptically calm condition lasts long. Since the structure and intensity of the MCs depend on geography and topographical allocation, land surface coverage, incoming solar radiation intensity and so on, it makes the estimates of source-reception relationship and long-range atmospheric dispersion more diffi-culty. It concluded that it is impossible for a pollution model to correctly simulate smokes transport using only the synoptic station data, since the mesoscale information can not be resolved from these datasets.
Seasonality of the Interaction between Convection over the Western Pacific and General Circulation in the Northern Hemisphere
Hu Zengzhen, Tsuyoshi Nitta
1997, 14(4): 541-553. doi: 10.1007/s00376-997-0072-3
The seasonality of the interaction between convection over the western Pacific and general circulation in the Northern Hemisphere (NH) is analyzed in the present paper with singular value decomposition (SVD) and empirical orthogonal function (EOF) analysis approaches, based on 500 hPa monthly mean geopotential height data and high-cloud amount data. The analyses demonstrate that coupled dominant patterns in the interaction between the convection over the western Pacific and the general circulation in NH are different in various seasons. In spring, the convection over the western Pacific is closely related with the western Atlantic (WA) and North Pacific (NP) like patterns of the general circulation in NH, and some associations between the WA and NP like pat?terns and the El Ni?o / Southern Oscillation (ENSO) cycle are also existed. The Pacific Japan (PJ) pattern is the dom?inant pattern in the interaction between the interannual variabilities of the convection over the western Pacific and the general circulation in NH summer. The WA like pattern and 3-4 year period oscillation are also relatively obvious for the summer case. In autumn, the convection over the western Pacific is closely linked with the Eurasian (EU) like pattern and the Atlantic oscillation in the general circulation in NH, it is suggested that in autumn the vitiation of convective activity over the western Pacific is largely affected by the general circulation anomaly (cold air from high latitudes) through EU like teleconnection pattern. Abrupt change happened by the end of 1980’s in the autumn interaction. The strong interaction between the western Pacific (WP) and EU like patterns in the general circulation in NH and the convection over the western Pacific and a linear trend of increasing of this interaction are also suggested in winter. It is also demonstrated that the interaction in summer and winter is stronger than in the transition seasons (spring and autumn).
The Interannual Variability and Predictability in a Global Climate Model
WangHuijun, Xue Feng, Bi Xunqiang
1997, 14(4): 554-562. doi: 10.1007/s00376-997-0073-2
The interannual variabilities of the climatological simulation (V1) and the AMIP (Atmospheric Model intercomparison Project) simulation (V2) by the IAP 9-Level Atmospheric General Circulation Model are studied and discussed in this paper. Based on the analysis of ratio of variability (R) of above two simulations the predictability of the model on the interannual climate variation are studied as well. Results show that V2 is bigger than V1 generally and V2 is more comparable to the real variability of the atmosphere, the major difference of VI and V2 is in the tropics, for temperature and geopotential height the predictability is higher in the tropics while in the extra-tropics there is almost no predictability and the predictability is bigger in higher level thin in lower level. The predictability for precipitation is generally low in the globe, and generally the predictability is high in the tropical eastern Pacific for the lower level. This study suggests that the possible way of increasing the model predictability is the improvement of land surface process modelling and the inclusion of the interannual variations of the land surface conditions (snow cover, albedo, soil moisture, etc.) as the forcing factor for climate modelling and prediction.
Multispectrum Method and the Computation of Vapor Equation
Ji Zhongzhen, Wang Bin
1997, 14(4): 563-568. doi: 10.1007/s00376-997-0074-1
In order to improve the practicality of spectral method and the efficiency of computation, the multi-spectrum method is proposed on the basis of multi-grid method. Coarse spectra are used to compute the slow nonlinear part (including physical process), while fine spectra are used to compute the fast linear part. This method not only can re-duce computation time, but also can obtain computational efficiency similar to that from only fine spectra. Thus, it is an economical numerical method. Both explicit complete-square-conservation scheme and multispectrum scheme are used to improve IAP L9 T42 spectral climate models, with and without physical forcings respectively, and the ad-vantage of reducing computation time is obtained satisfactorily. In order to overcome the difficulty that vapor equa?tion is very sensitive to the change of time step, the square-conservation semi-Lagrangian scheme is used to solve vapor equation. Because the semi-Lagrangian scheme has the property or square-conservation, computational in?stability can be avoided. When time step becomes longer with the semi-Lagrangian Scheme, through numerical ex?amples, the vapor transportation can be depicted objectively and the effect of precipitation simulation can be modi?fied.
Parallel Computing of a Climate Model on the Dawn 1000 by Domain Decomposition Method
Bi Xunqiang
1997, 14(4): 569-572. doi: 10.1007/s00376-997-0075-0
In this paper the parallel computing of a grid-point nine-level atmospheric general circulation model on the Dawn 1000 is introduced. The model was developed by the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS). The Dawn 1000 is a MIMD massive parallel computer made by National Research Center for In-telligent Computer (NCIC), CAS. A two-dimensional domain decomposition method is adopted to perform the par-allel computing. The potential ways to increase the speed-up ratio and exploit more resources of future massively parallel supercomputation are also discussed.