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1998 Vol. 15, No. 3

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The Development and Initial Tests of an Atmospheric Model Based on a Vertical Coordinate with a Smooth Transition from Terrain Following to Isentropic Coordinates
D. R. Johnson, Zhuojian Yuan
1998, 15(3): 283-299. doi: 10.1007/s00376-998-0001-0
An atmospheric model (η model) is developed by modifying the UW θ-σ hybrid model. In the η model, the vertical coordinate transforms smoothly from terrain following to isentropic coordinates. The model is developed to capitalize on the inherent advantage of numerical modeling in isentropic coordinates and to eliminate the interface between the sigma planetary boundary layer and isentropic free atmosphere present in the UW θ-σ model. This formulation provides the potential for the data assimilation and the application of higher order schemes. This paper describes the structure of the η model and presents results from initial numerical experiments. The first experiment tests the capability of the η model for simulating the baroclinic development process. In the 48-hr numerical weather forecast experiment, the η model produces reasonable precipitation and synoptic fields at all levels which are similar to those from the UW θ-σ model. The second and third experiments test the capability of the η model for conserving 1) the joint distribution of isentropic potential vorticity (IPV) and proxy ozone and 2) equivalent potential temperature under frictionless and isentropic conditions. These experiments show that distributions of IPV and proxy ozone in the pure isentropic domain and the distributions of prognostic and diagnostic equivalent potential temperature in the model domain remain highly correlated to day 10.
Numerical Experiment for the Impact of the Ozone Hole over Antarctica on the Global Climate
Chen Yuejuan, Zhang Hong, Bi Xunqiang
1998, 15(3): 300-311. doi: 10.1007/s00376-998-0002-z
A numerical experiment has been carried out with IAP (Institute of Atmospheric Physics) 9-layer general circu-lation model to investigate the influence of the Antarctic Ozone Hole on the global climate. The results show that the changes of total amount of ozone over higher latitude and polar region of the Southern Hemisphere affect not only the climate in the Southern Hemisphere, but also that in the Northern Hemisphere significantly. In the next spring, al-though the total amount of ozone over Antarctica has returned to the normal value, the influences of Ozone Hole still exist.
Low-Frequency Waves Forced by Large-scale Topography in the Barotropic Model
Fu Zuntao, Liu Shikuo, Fu Caixia
1998, 15(3): 312-320. doi: 10.1007/s00376-998-0003-y
A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency waves mostly is maximal height of topography and topographic slope. The former makes frequency of topographic Rossby waves decrease, the latter makes Rossby waves instable. Moreover, when topographic slope is appropriate, it can also make Rossby waves turn into low-frequency waves.
The Water-Bearing Numerical Model and Its Operational Forecasting Experiments Part II: The Operational Forecasting Experiments
Xu Youping, Xia Daqing, Qian Yueying
1998, 15(3): 321-336. doi: 10.1007/s00376-998-0004-x
The water-bearing numerical model is undergone all round examinations during the operational forecasting ex-periments from 1994 to 1996. A lot of difficult problems arising from the model’s water-bearing are successfully re-solved in these experiments through developing and using a series of technical measures. The operational forecasting running of the water-bearing numerical model is realized stably and reliably, and satisfactory forecasts are obtained.
Seasonal and Interannual Variations of Upper Tropospheric Water Vapor Band Brightness Temperature over the Global Monsoon Regions
Qian Weihong, Zhu Yafen, Xie An, Ye Qian
1998, 15(3): 337-345. doi: 10.1007/s00376-998-0005-9
The upper-troposphere water vapor (UTWV) band brightness temperature (BT) dataset derived from the High-resolution Infrared Radiation Sounder (HIRS) channel 12 of the National Oceanic and Atmospheric Admini-stration (NOAA) polar satellites from 1979 to 1995 is used to analyze the seasonal and interannual variations for the global monsoon regions. Results show that (i) there are three major regions where the UTWV band BT varies significantly with season, i.e., South Asia, the western coastal South-North America tropical region and the low-lati-tude African region; (ii) UTWV band BT clearly reveals the water vapor temporal / spatial features as well as the at-mospheric circulation structure over the low-latitude during the monsoon onset; and (iii) there is a remarkable rela-tionship between the interannua] variation of the UTWV band BT over the monsoon regions and the sea surface tem-perature anomaly in the eastern equatorial Pacific.
On the Forcing of the Radial-vertical Circulation within Cyclones-Part 1: Concepts and Equations
D. R. Johnson, Zhuojian Yuan
1998, 15(3): 346-369. doi: 10.1007/s00376-998-0006-8
Following the theoretical result of Eliassen, the Sawyer-Eliassen equation for frontal circulations and the equa-tion for forcing the meridional circulation within a circum polar vortex are extended in isentropic coordinates to des-cribe the forcing of the azimuthaHy averaged mass-weighted radial-vertical circulation within translating extratropical and tropical cyclones. Several physical processes which are not evident in studies employing isobaric coordinates are isolated in this isentropic study. These processes include the effects of pressure torque, inertia! torque and slorm translation that are associated with the asymmetric structure in isentropic coordinates. This isentropic study also includes the effects of eddy angular momentum transport, diabatie heating and fractional torque that are common in both isentropic and isobaric studies. All of the processes are modulated by static, inertial and baroclinic stabilities. Consistent with the theoretical result of Eliassen, the numerical solution from this isentropic study shows that the roles of torque, diabatic heating and hydrodynamic stability in forcing the radial-vertical circulation within stable vortices are that 1) positive (negative) torque which results in the counterclockwise (clockwise) rotation of vortices al?so forces the outflow (inflow) branch of the radial-vertical circulation, 2) diabatic heating (cooling) forces the ascent (descent) branch of the radial-vertical circulation and 3) for given forcing, the weaker hydrodynamic stability results in a stronger radial-vertical circulation. It is the net inflow or convergence (net outflow or divergence), vertical mo?tions and the associated redistribution of properties that favor the evolution of vortices with colorful weather events. Numerical solutions of this isentrcpic study ate given in companion articles. The relatively important contribu?tion of various physical processes to the forcing of the aamulhally-averaged mass-weighted radial-vertical circula?tion within different translating cyclones and in their different stages of development will be investigated.
A Two-Dimensional Zonally Averaged Ocean Carbon Cycle Model
Xu Yongfu, Wang Mingxing
1998, 15(3): 370-379. doi: 10.1007/s00376-998-0007-7
An ocean carbon cycle model driven by a constant flow field produced by a two-dimensional thermohaline circu-lation model is developed. Assuming that the biogenic carbon in the oceans is in a dynamic equilibrium, the inorganic carbon cycle is investigated. Before the oceanic uptake of CO2 is carried out, the investigation of 14C distributions in the oceans, including natural and bomb-produced 14C, is conducted by using different values of the exchange coefficient of CO2 for different flow fields (different vertical diffusivities) to test the performance of the model. The suitable values of the exchange coefficient and vertical diffusivities are chosen for the carbon cycle model. Under the forcing of given preindustrial atmospheric CO2 concentration of 280 ppmv, the carbon cycle model is integrated for seven thousand years to reach a steady state. For the human perturbation, two methods including the prescribed at-mospheric pCO2 and prescribed industrial emissions are used in this work. The results from the prescribed atmospher-ic pCO2 show that the oceans take up 36% of carbon dioxide released by human activities for the period of 1980-1989, while the results from the prescribed industrial emission rates show that the oceans take up 34% of car-bon dioxide emitted by industrial sources for the same period. By using the simple method of subtracting industrial emission rate from the total atmosphere+ocean accumulating rate, it can be deduced that before industrial revolution a non-industrial source exists, while after 1940 an extra sink is needed, and that a total non-industrial source of 45 GtC is obtained for the period of 1790-1990.
Seasonal and Spatial Variation of Radiative Effects of Anthropogenic Sulfate Aerosol
Qian Yun, Wang Hongqi, Fu Congbin, Wang Zifa
1998, 15(3): 380-392. doi: 10.1007/s00376-998-0008-6
On the basis of the emission data of the industrial sulphur dioxide (SO2) and observed climate fields over East Asia, the distribution of anthropogenic sulfate aerosol (SO) with seasonal variation in the troposphere is simulated and analyzed by a regional sulfur transport model, and the direct radiative effects of SO under different weather conditions are also calculated using the discrete ordinate method. The results show that the concentration of SO has significant seasonal and spatial variations resulting from the effects of SO2 emission source and precipita-tion and wind fields. Both the concentration of SO2 and its radiative forcing have the largest values in October and the lowest in July. SO causes the decrease of the radiation flux absorbed by earth-atmosphere and the cooling of air temperature by scattering more solar radiation back into space. Besides, the radiative and climatic effects of SO are related to the types and height and optical thickness, etc., of the clouds.
Numerical Studies on Urban Heat Island Associated with Urbanization in Yangtze Delta Region
Tang Youhua, Miao Manqian
1998, 15(3): 393-403. doi: 10.1007/s00376-998-0009-5
The impact of modifications of the surface characteristics on local climate is simulated with a numerical mesoscale model in the Yangtze delta region, east of China. The simulated reference case with the current surface properties shows that there is urban heat island in Shanghai city which is located in the center of this region. The mod-ifications of surface characteristics due to the urbanization around Shanghai will lead to the change of local air circu-lation and redistribution of surface temperature. Simulation for this case shows that the urbanization around Shanghai has little effect on Shanghai, but will extend the area of heat island. Another case is assumed that the area of grassland is kept as 50% while the urban areas are extended. Compared with the case of pure urbanization, the max-imum reduction of surface air temperature is 2.0oC in the daytime and 2.3oC at night.
The Solitary Waves of the Barotropic Quasi-Geostrophic Model with the Large-scale Orography
Chen Jiong, Liu Shikuo
1998, 15(3): 404-411. doi: 10.1007/s00376-998-0010-z
Starting from a modified barotropic quasi-geostrophic model equation, considering the actual situation of the large-orography of the Tibetan Plateau, neglecting its slope in x direction, and using the reductive perturbation method, then the solitary waves are obtained. The results show that the orography is essential factor exciting solitary Rossby waves in a flow without shear.
Cloud Feedback on SST Variability in the Western Equatorial Pacific in GOALS / LASG Model
Liu Hui, Zhang Xuehong, Wu Guoxiong
1998, 15(3): 412-423. doi: 10.1007/s00376-998-0011-y
The cloud feedback on the SST variability in the western equatorial Pacific in GOALS / LASG model is studied in this paper. Two versions of the model, one with the diagnostic cloud and another with the prescribed cloud, are used. Both versions are integrated for 45 years. It is found that in the prescribed cloud run, the SST variability in the western equatorial Pacific is mainly of interdecadal time scale and the interannual variability is very weak. In the diagnostic cloud run, however, the interdecadal SST variability is depressed much and the interannual SST variability becomes much significant. The mechanism for the feedback is then explored. The variability of sea surface temperature (SST) in the western equatorial Pacific is found to be controlled mainly by the zonal wind anomaly, through the process of upwelling / downwelling in both versions. Then it is found that in the diagnostic cloud case, the negative feedback of the solar short wave (SW) flux acts significantly to balance the effect of upwelling / downwelling in addition to the la?tent flux. In addition, the variability of the SW flux is shown to be closely related to the variability of the middle and high cloud covers. Therefore, the negative feedback of the SW surface flux may have significant contribution to the cloud feedback on the SST variability.
Relationships between Rainy Days, Mean Daily Intensity and Seasonal Rainfall in Normal, Flood and Drought Years over India
C. V. Singh
1998, 15(3): 424-432. doi: 10.1007/s00376-998-0012-x
There are limitations in using the seasonal rainfall total in studies of Monsoon rainfall climatology. A correlation analysis of the individual station seasonal rainfall with all India seasonal mean rainfall has been made. After taking the significance test (strictly up to 5% level) the stations which are significantly correlated have been considered in this study in normal, flood and drought years respectively. Analysis of seasonal rainfall data of 50 stations spread over a period of 41 years suggests that a linear relationship fits better than the logarithmic relationship when seasonal rain-fall versus number of rainy days is studied. The linear relationship is also found to be better in the case of seasonal rainfall versus mean daily intensity.