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2001 Vol. 18, No. 1

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An Oceanic General Circulation Model in Pressure Coordinates
Huang Ruixin, Jin Xiangze, Zhang Xuehong
2001, 18(1): 1-22. doi: 10.1007/s00376-001-0001-9
A new oceanic general circulation model in pressure coordinates is formulated. Since the bottom pressure changes with time, the vertical coordinate is actually a pressure-σ coordinate. The numerical solution of the model is based on an energy-conservation scheme of finite difference. The most important new feature of the model is that it is a truly compressible ocean model and it is free of the Boussinesq approxima tions. Thus, the new model is quite different from many existing models in the following ways: 1) the exact form of mass conservation, 2) the in-situ instantaneous pressure and the UNESCO equation of state to calculate density, 3) the in-situ density in the momentum equations, 4) finite difference schemes that conserve the total energy. Initial tests showed that the model code runs smoothly, and it is quite stable. The quasi-steady circulation patterns generated by the new model compare well with existing models, but the time evolution of the new model seems different from some existing models. Thus, the non-Boussinesq models may provide more accurate information for climate study and satellite observations.
Sensitivity of Numerical Simulations of the East Asian Summer Monsoon Rainfall and Circulation to Different Cumulus Parameterization Schemes
Huang Ronghui, Wu Bingyi, Sung-Gil Hong, Jai-Ho Oh
2001, 18(1): 23-41. doi: 10.1007/s00376-001-0002-8
A 5-level spectral AGCM (ImPKU-5LAGCM) is used to examine the sensitivity of the simulated results of the summer monsoon rainfall and circulation in East Asia to different cumulus parameterization schemes in the climatological-mean case and in the cases of weak and strong Asian summer monsoons,respectively. The results simulated with the Arakawa-Schubert's(hereafter A-S's), Kuo's and Manabe's cumulus parameterization schemes show that these simulated distributions of the summer monsoon rainfall and circulation in East Asia depend strongly on the cumulus parameterization schemes either in the climatological-mean case or in the cases of weak and strong Asian summer monsoons. From the simulated results, it might be shown that the Kuo scheme appears to be more suitable for the simulation of the summer monsoon rainfall and circulation in East Asia than the A-S scheme or the Manabe scheme, although the A-S scheme is somewhat better in the simulations of the tropical rainfall. This might be due to that the Kuo's cumulus parameterization scheme is able to reflect well the characteristics of rainfall cloud system in the East Asian summer monsoon region, where the rainfall system used to be a mixing of cumulus and stratus.
The Effects of Climate on Development of Ecosystem in Oasis
Pan Xiaoling, Chao Jiping
2001, 18(1): 42-52. doi: 10.1007/s00376-001-0003-7
When vegetation and bare soil coexist, in consideration of some ecological conditions of plant, the total evapotranspiration rate of the oasis and the temperature of vegetation and soil in different climatic and ecological conditions are calculated by using the thermal energy balance equations of vegetation and soil.The evapotranspiration rate depends on climatic and ecological conditions. In some conditions,quasi-bifurcation and multi-equilibrium state appear in the solutions of evapotranspiration rate in the are as covered by small part of vegetation.
Simulation of Climate Change Induced by CO2 Increasing for East Asia with IAP/LASG GOALS Model
Guo Yufu, Yu Yongqiang, Liu Xiying, Zhang Xuehong
2001, 18(1): 53-66. doi: 10.1007/s00376-001-0004-6
Two simulations, one for the control run and another for the perturbation run, with a global coupled ocean-atmosphere-land system model (IAP / LASG GOALS version 4) have been carried out to study the global warming, with much detailed emphasis on East Asia. Results indicate that there is no climate drift in the control run and at the time of CO2 doubling the global temperature increases about 1.65℃. The GOALS model is able to simulate the observed spatial distribution and annual cycles of temperature and precipitation for East Asia quite well. But, in general, the model underestimates temperature and overestimates rainfall amount for regional annual average. For the climate change in East Asia, the temperature and precipitation in East Asia increase 2. l℃ and 5% respectively, and the maximum warming occurs at middle-latitude continent and the maximum precipitation increase occurs around 25°N with reduced precipitation in the tropical western Pacific.
On the Helicity Dynamics of Severe Convective Storms
Fei Shiqiang, Tan Zhemin
2001, 18(1): 67-86. doi: 10.1007/s00376-001-0005-5
A well-documented supercell thunderstorm occurred in Del City, Oklahoma, on 20 May 1977 is successfully simulated by a three-dimensional, nonhydrostatic storm-scale numerical model ARPS. With the numerical simulated data of the storm, the structure and evolution of the helicity, superhelicity and their dynamical influences on the development of the storm are investigated. The initial helical structure of environmental flow is favorable to the development of storm. In the developing stage of storm, low helicity is beneficial to the nonlinear energy cascade. However, the high helicity is of help to maintain the energy of convection cell at the mature stage of storm, and lead to a long life cycle of convective cell. Rotating thunderstorm has a tendency of adjusting to the Beltrami flow structure and tends to a higher helicity of flow.The negative superhelicity could lead to an increase of helicity. Superhelicity is negative in the initial developing process of storm however the superhelicity is positive in the mature stage of storm. Therefore, the superhelicity can be used as an indicator of the mature degree of convective storm.
The Maintenance of the Blocking over the Ural Mountains during the Second Meiyu Period in the Summer of 1998
Li Shuanglin, Ji Liren, Lin Wantao, Ni Yunqi
2001, 18(1): 87-105. doi: 10.1007/s00376-001-0006-4
The 1998 summer-time floods at the Yangtze River basin of China, the severest in last 50 years or so,directly resulted from the abnormal extension of Meiyu (rainy season), which was related to a weak East Asian summer monsoon and persistent anomalies of extratropical circulation. The long persistence of blocking over the Ural Mountains is a conspicuous feature. The physical processes responsible for the prolonged maintenance of this key system are investigated in terms of internal forcing (transient eddy upon basic flow)and external forcing (tropical heating forcing) via diagnosis and numerical experiments in the paper. Using the adjoint method, the location and structure of optimal perturbations favorable for the development and maintenance of Ural blocking are identified, which shows an apparent coincidence with the observed storm track at the eastern Atlantic to Europe sector. The diagnosis of E-vector and the response of baroclinic stationary wave to transient forcing both suggest further that the enhanced transient eddy activity favors the occurrence and maintenance of positive anomalies. The upper-level jet and heat sources (sinks) during that period are calculated, and the results indicate that the anomaly of upper jet and tropical heating is evident. The ensemble forecasting experiments by a GCM, IAP T42L9 show that the anomalous heating over the tropics, especially over the central-western Pacific and Atlantic, favors the formation of positive anomalies of height at the Ural region. Finally, a self-sustain mechanism of positive anomalies through two-way interaction between planetary stationary wave and transient eddy under the stimulation of anomalous tropical heating is proposed.
Interannual Variability of Atmospheric Heat Source/Sink over the Qinghai-Xizang (Tibetan) Plateau and its Relation to Circulation
Zhao Ping, Chen Longxun
2001, 18(1): 106-116. doi: 10.1007/s00376-001-0007-3
Based on the 1961-1995 atmospheric apparent heat source/sink and the 1961-1990 snow-cover days and depth over the Qinghai-Xizang Plateau (QXP) and the 1961-1995 reanalysis data of NCEP/NCAR and the 1975-1994 OLR data, this paper discusses the interannual variability of the heat regime and its relation to atmospheric circulation. It is shown that the interannual variability is pronounced, with maximal variability in spring and autumn, and the variability is heterogeneous horizontally. In the years with the weak (or strong) winter cold source, the deep trough over East Asia is to the east (or west) of its normal, which corresponds to strong (or weak) winter monsoon in East Asia. In the years with the strong (or weak) summer heat source, there exists an anomalous cyclone (or anticyclone) in the middle and lower troposphere over the QXP and its neighborhood and anomalous southwest (or northeast) winds over the Yangtze River valley of China, corresponding to strong (or weak) summer monsoon in East Asia. The summer heat source of the QXP is related to the intensity and position of the South Asia high. The QXP snow cover condition of April has a close relation to the heating intensity of summer. There is a remarkable negative correlation between the summer heat source of the QXP and the convection over the southeastern QXP, the Bay of Bengal, the Indo-China Peninsula, the southeastern Asia, the southwest part of China and the lower reaches of the Yangtze River and in the area from the Yellow Sea of China to the Sea of Japan.
Numerical Simulation Study for the Structure and Evolution of Tropical Squall Line
Sun Tingkai, Tan Zhemin
2001, 18(1): 117-138. doi: 10.1007/s00376-001-0008-2
The occurrence and evolution of an oceanic tropical squall line observed on 22 February 1993 during TOGA-COARE over the equatorial Pacific Ocean were simulated by use of a three-dimensional,nonhydrostatic storm-scale numerical model ARPS. The capacity of ARPS to simulate such tropical squall line was verified. The structure and dynamic mechanism of the squall line were discussed in details as well.The impacts of the different microphysical process that including the ice phase and warm rain schemes on structure and evolution of the squall line were investigated by the sensitive experiment.The simulations of the three-dimensional structure and evolution of the squall line are closely related with the observations when the proper microphysical processes were employed. The more latent heating released in the ice phase processes associated with the freezing process leads to strengthening deep convection due to the vertical gradient of buoyancy, which results in a long life of the convective system. In contrast, the warm rain process is characterized by short life period, more pronounced rearward tilt structure and extension of stratiform cloud.
Validation of IAP94 Land Surface Model over the Huaihe River Basin with HUBEX Field Experiment Data
Yang Xiaosong, Lin Zhaohui, Dai Yongjiu, Guo Yufu
2001, 18(1): 139-154. doi: 10.1007/s00376-001-0009-1
Off-line experiments have been conducted with IAP94 land surface model on different surface types (cropland, forest and paddy field) in different seasons (spring, summer and autumn) over the Huaihe River basin. The simulated energy fluxes and canopy temperature by IAP94 agree quite well with the observations,simulation results also show that IAP94 can successfully simulate the tendency of total soil water content variation. The comparison results between simulation and observation indicate that strong evaporation at the paddy field in summer should be paid more attention to within the land surface models, and model s performance leads to the conclusion that IAP94 is capable of reproducing the main physical mechanisms governing the land-surface processes in the East Asian semi-humid monsoon region.