Showing papers by "Nanjing University of Information Science and Technology published in 2004"

Preliminary analysis on boundary climate effects between oasis and desert in the north margin of the Taklimakan Desert

Abstract: According to the analysis to the climatic data of Xiao Tang in desert, Lun Tai in oasis during 1992 to 1997, the following viewpoints were noted: (1)The air temperature of desert is lower than the one of oasis in winter, the air temperature rise gradually from oasis to desert in summer. The diurnal range and annual range of air temperature in desert is wide than the one in oasis. (2)The precipitation of oasis is more than the precipitation of desert. The difference of seasonal precipitation is great in desert, the most of precipitation is in warm period, it is basic characteristics that mean-square diviations of precipitation are big in desert. Not only large-scale weather system affects the precipitation in desert, but also violent local thermal circulation can form the local unstable precipitation in desert. (3)The Humidity of desert is lower than humidity of oasis and the evaporation amount of desert is bigger than evaporation amount of oasis. The evaporation capableness of desert is mighty, the difference of seasonal evaporation amount is great in desert and the 77% of annual mean evaporation amount is in summer and spring.(4)The days of sand blown by wind weather in desert are more than the one of oasis. The wind speed in desert is faster than the one of oasis. These indicate that the difference is apparent between desert and oasis. This is caused by differences of Landscape and water amount. The exploitation and utilization on oasis enlarge this difference.

Three-Dimensional Numerical Simulation of a Strong Convective Storm

Abstract: The fully elastic three-dimensional convective storm model(IAP-CSM3D) developed by the Institute of Atmospheric Physics(IAP),was used to simulate the strong convective storm occurred in Hunan Province on April 23,2004.A squall line swept over the most of Hunan Province,and the torrential rain(three-hour precipitation more than 50 mm) occurred in Shaoyang,Loudi,Changsha and Liuyang from 08:15 to 11:42BST.Meanwhile hailstones attacked Changsha and Zhuzhou from 12:37 to 14:25BST.The distribution and evolution of the macro-physical as well as micro-physical quantities of the strong convection process,such as wind field structure,radar echo,water content,etc.are simulated,and the formation mechanism of hailstones in the storm is analyzed.The simulation results indicate that the auto-conversion of frozen drops and graupels(CNfh,CNgh) are the main sources of the hailstones in the strong convective storm studied,but the contribution of frozen drops(CNfh) is greater than that of graupels(CNgh).The growth of hailstones mainly depends on collecting supercooled water(CLch,CLrh).The Doppler weather radar observations are compared with the simulated airflow structure,and results indicate that the change of divergence with height observed is consistent with the airflow structure simulated,and that the reflectivity and echo top output from the model are close to those observed.

Response of different crop growth and yield to enhanced UV-B radiation under field conditions

Abstract: Enhanced UV-B radiation due to stratospheric ozone depletion may have impacts on the productivity of agricultural crops. Which crop will be more sensitive to increased UV-B has received little attention. This paper presents a comparative study of the effects of supplemental UV-B on plant height, leaf area, biomass and yield among soybean, cotton, corn and wheat which were cultivated in fields in Nanjing, China. The experimental results showed that the four crops response to enhanced UV-B irradiation was shortened plant height, decreased leaf area and reduced biomass and yield of crops. Using the same criteria, the response of soybean and cotton to elevated UV-B is bigger than that of wheat and corn. RI (response index) is an integrated index which is the accumulation of relative change in plant height, leaf area, biomass and yield, reflecting general impact of increased UV-B on crops. The results suggested that the RI for the four crops was minus, demonstrating a negative impact of enhanced UV-B on the crops. According to the RI, the soybean and cotton belong to the sensitive plants category, wheat is a moderately sensitive plant and corn is a tolerant plant.

Effect of enhanced UV-B radiation combined with other climate stressors on winter wheat

Abstract: Ultraviolet radiation-B (UV-B) would increase due to the Ozone depletion. Global climatic factors, such as temperature, precipitation, evapotranspiration, soil moisture and CO 2 content, are changing because of the increase of greenhouse emission and the destruction of ecosystems. Climate stress factors including enhanced UV-B irradiance have effects on crop production. Many studies have assessed the effects of enhanced UV-B on crops and impacts of global climatic change on crops separately. However, when UV-B effects were discussed, other environmental stress factors were generally neglected. It is well-known that crops in nature are seldom affected by only a single stress factor, such as UV-B radiation. The impacts of enhanced UV-B radiation can be greatly increased or decreased by other environmental stress factors. In this paper, through field and plant growth chambers experiments, combined effects of enhanced UV-B radiation with other environmental stress factors including solar visible light, temperature and soil moisture content on winter wheat were investigated. The experimental results showed that enhanced UV-B irradiance can restrain growth and development of winter wheat, which leads to reduction of plant height, leaf area, and slowing physiological activity and decreasing biomass and yield of winter wheat. The response of winter wheat to enhanced UV-B varied under different UV-B intensity and its combination with other environmental stress factors.

Effect of Horizontal Nonuniformity of Diabatic Heating on Tropical Cyclone Intensity and Structure

Abstract: The eect of the horizontal variation of diabatic heating on the tropical cyclone intensity and structure is studied in this paper. According to the potential vorticity (PV) equation in axis-symmetric cylindrical coordinates, PV disturbance caused by the radial dierence of diabatic heating is positive (negative) inside (outside) the maximum heating radius, implying that the radial nonuniformity of diabatic heating should contribute positively to the intensity of a tropical cyclone while negatively to its size. A primitive equation model is then used to get some quantitative ideas on the problem. Results show that the modeled tropical cyclone weakens by about 20% but is larger in size if the eect of horizontal variety of convective heating is excluded in thermodynamic and dynamic equations. The PV disturbance originated from the horizontal nonuniformity of diabatic heating is positive inside the maximum heating radius and negative outside, in consistent with the PV equation analyses. The maximum disturbance (both negative and positive) appears around the maximum heating level and their magnitude is comparable to that generated by vertical variance of heating. It is concluded that the eect of the horizontal heat nonuniformity on the intensity and structure of TC cannot be neglected.

Atmospheric Free Modes and Subtropical High

Abstract: By numerically solving the unforced and inviscid nonlinear barotropic vorticity equation through the quasi-Newton method, the steady free modes are obtained, which are very similar to the real o w elds, and their scatter diagram of ( ;q) display segmented linear or nonlinear relations. From this scheme a range of free modes have been achieved, each corresponding to one of the atmospheric o w elds. In the study of changes in the western Pacic subtropical high (WPSH) as revealed by free modes it is discovered that the west-extension/northward jump and east-movement/southward withdrawal of WPSH for the free mode occur 5-10 days ahead of the changes in the high as shown in the 500 hPa geopotential height eld. Besides, a standard mode technique is adopted to investigate the stability of the free modes, indicating that the faster the instable mode grows, the closer it comes to a quasi-steady state. Especially, the instable mode with its quasi-steady state growing the fastest bears a correspondence with the high in steady intensication, leading to the fact that the persistent strengthening of the high is likely to be caused by the instable free modes with the fastest growth that are of quasi-steady state, or experience long-period low-frequency variation.