Vol.15, NO.1, 2004

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THE MECHANISMOF A SAND STORMOVER CHINA IN MARCH 2002
Xiao Xianjun, Liu Huanzhu, Song Zhenxin, He Jinhai
2004, 15(1): 1-9.
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Abstract:
A numerical model from Shao Yaping is applied to the sand storm over China in March 2002, and the predictions are in good agreement with meteorological records and satellite images. A dynamical diagnose based on the data from model presents more information than real meteorology record about the mechanism of the sand storm. It is caused by the frontogenesis of cold front connected with Menggu cyclone. Large amount of available potential energy convert to dynamic energy in the baroclinic mesosphere. It results in frontogenesis. As the strong normal share of the wind, turbulent fluctuation is strengthened and the sands are raised up from the surface ground. The wind speed in the atmosphere of the low level has a horizontal share and this pushes the sands in the atmosphere aggregate, so the visibility descends. A strong sandstorm is produced.
A CALCULATION OF CONVECTIVE ENERGY AND THE METHOD OF SEVERE WEATHER FORECASTING
Li Yaodong, Gao Shouting, Liu Jianwen
2004, 15(1): 10-20.
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Abstract:
Two methods-pseudo equivalent potential temperature conservation and reversible moist adiabatic process are reviewed to deal with moist adiabatic process .Modified convective available potential energy (MCAPE) is int roduced to modify CAPE by presenting the gravitational effect of the condensed liquid water in upward convection .Modified downdraft convective available potential energy (MDCAPE) is defined to modify DCAPE by considering the dragging effect of liquid water .Real case studies show that liquid water plays more significant roles in rising parcel by diminishing CAPE largely than it does in downward f low by increasing DCAPE tenderly .Reversible moist adiabatic process is recommended in calculating MCAPE and MDCAPE .A synthetic multi-indicator superposition method is developed to predict the unstable and severe weather area based on the diagnosis of numerical model output .Experiment shows that the skill is practicable to both MM5 and Chinese National Meteorological Center T106 model output s.
A CASE STUDY OF PERSISTENT HEAVY RAINFALL OVER HUNAN PROVINCE IN JULY 1996
Zhang Xiaoling, Tao Shiyan, Zhang Shunli, Zhang Qingyun
2004, 15(1): 21-31.
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Abstract:
The heavy rainfall over Hunan Province in July 1996 was studied. The main conclusions are made as follows: (1) Persistent rainstorms causing flash-flood in Hunan Province lied in the front of 500 hPa short wave troughs. (2) MCS generated and detained in the same area, which is the direct reason causing lasting heavy rainfall. (3) By warm advection in the lower troposphere and other large-scale forcing, the upper troughs maintained over the middle of the Yangtze River Basin, which brought continuous lifting movement in the rainstorm area. At the same time, continuous moisture convergence and potential instable energy transport in the lower layers provided enough water and energy for lasting heavy precipitation over the rainstorm area。
CHARACTERISTICS OF CHANGE AND TRANSPORTOF AEROSOLS IN THE MIDDLE AND UPPER TROPOSPHERE AND STRATOSPHERE OVER INDIAN OCEAN AND CHINA IN 1984-2000
Wang Kaicun, Li Weiliang, Bai Lijie
2004, 15(1): 32-39.
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Abstract:
The latest version (6.0) daily aerosols extinction dataset of the 1.020 μm zone SAGE Ⅱ was analyzed, and the characteristics of transport and change of aerosol optical depth in the middle and upper troposphere and the stratosphere (above 10 kilometer high) was given. The results show that aerosol optical depth in the low latitude is larger than that in the higher latitude. There are three high value centers over the island in Indian Ocean. The high value centers of aerosol optical depth are corresponding with the high value of up flow in the middle and upper troposphere. Comparing to the average of the 17 years (1984—2000), latest 6 years the aerosol optical depth from the Bengal Bay to the southeast of the Tibetan Plateau increases distinctively. Contrary to the middle and eastern of China, the aerosol optical depth over the eastern of China is decreased. Aerosol optical depth has three longitudinal increasing zones and two longitudinal decreasing zones. The Brewer-Dobson circulation between the middle latitude and the equator area causes these longitudinal change zones. This transporting of aerosols between the lower layer and middle and upper layer atmosphere may cause important climate change。
A SOIL-WATER BALANCE MODEL UNDER WATERLOGGING CONDITION IN WINTER WHEAT
Hu Jichao, Cao Weixing, Luo Weihong
2004, 15(1): 41-50.
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Abstract:
Based on soil moisture budget method, a soil water balance model for waterlogged winter wheat field was developed, which can be coupled with crop growth model. In order to simulate the soil waterlogging status, the calculation of capillary rise from the water table and the functions of hydraulic conductivity characteristics were incorporated. The simulated values of daily evapotranspiration were verified by the dataset from the pot experiments. The model was validated for water table and soil water contents for 0~10 cm, 10~20 cm, 20~30 cm, 30~40 cm and 40~50 cm soil layers using the observed data in Jingzhou and Jintan sites. Statistical analysis shows a good agreement between the simulated and observed data.
METHOD RESEARCH FOR OPERATIONAL DYNAMIC FORECASTING OF MAIZE YIELD IN NORTH-WESTOF CHINA
Wang Jianlin, Yang Feiyun, Song Yingbo
2004, 15(1): 51-57.
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Abstract:
The study of the relationship between climatic productivity and maize yield, and the relationship between soil water content and precipitation, and the relationship between soil water content and the sum of precipitation and initial soil water content in the Northwest China is showed that the correlation between climatic productivity of precipitation and maize yield, and the correlation between soil water content and the sum of precipitation and initial soil water content in local area are obvious. Based on them, Miami model of precipitation was improved by soil water content of sowing time and precipitation during maize growing period. The improved Miami model of precipitation is better in operational dynamic forecasting of maize yield trend every month. And also, it is practicable in assessment of precipitation influence on growth and development and dry matter accumulation of maize using this method in the Northwest China. But it is not suitable for the irrigating areas, because temperature and solar hour etc. Were not considered in this method.
PRIMARY ANALYSIS OF THE LONGEST-LASTING SNOWFALL IN BEIJING
Wang Yingchun, Qian Ting ting, Zheng Yongguang
2004, 15(1): 58-65.
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Abstract:
Five-day snowfall, which occurred in Beijing on 19—23 December 2002 and became the longest-lasting snowfall since 1841, is compositely analyzed. Five-day composite circumfluence showed that the snowfall took place in the constant zonal circulation. During the period, there was a strong Mongolia High on the surface. And the ridge of high pressure protruded southward our country’s east. On 850 hPa, Hetao area has a northward trough, and Beijing lied in the positive vortex of the trough. On 500 hPa, a front crossing Asia from west to east located 40~45°N. On 300 hPa, Beijing situated positive vortex of the axis of the jet, which was straightly zonal. The vertical section indicated that Beijing was convergent on the low-lever whereas divergent on the high-level. And there were two fronts. In a conclusion, Beijing was controlled by the large-scale circumfluence that was in favor of snowfall.The analysis of Huabei area during the continuous snowfall showed that the deformation field locating the north of trough had evident vapor convergence. Moisture flux indicated that vapor came from the return flow of the Yellow Sea, but not the return flow of Bo Sea. The warm advection in the east of Hetao trough was the cause of ascending.
STATISTIC CHARACTERISTICS OF THUNDERSTORM CLIMATE AT GUANGZHOU BAIYUN INTERNATIONAL AIRPORT IN THE LATE 46 YEARS
Zhang Meiping, Ao Shuzhen, Liu Xiang, Li Nianying
2004, 15(1): 66-73.
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Abstract:
The 46-year’s hourly observational information from 1956—2001 at Guangzhou Baiyun Airport is used to statistically analyzed the thunderstorm climatic characteristics and the wavelet transform is conducted. The results are obtained as follows: Year-averaged days of thunderstorm emergence at Baiyun Airport is 75.4 days. The early thunderstorm day in a year is generally on March 1, and the last thunderstorm day is generally on October 14. It is possible to occur a thunderstorm in any month a year, but occurring frequency of thunderstorm is much concentrated in April—September, the peak is in August and the minimum is in December. There are conspicuous seasonal and daily variations the thunderstorm. The variation period thunderstorm climatology has a 9—12 years, and the frequency is gradually decreased in the last 46 years.
THE INTERANNUAL AND INTERDECADAL VARIATIONS OF TROPICAL CYCLONES IN THE NORTHWEST PACIFIC AND ITS RELATIONSHIP WITH THE SOUTH ASIA HIGH
Zhang Yanxia, Qian Yongfu, Wang Qianqian
2004, 15(1): 74-80.
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Abstract:
By use of annual numbers of the Tropical Cyclone (TC) in 48 years (1949—1996) and monthly mean characteristic parameters of the South Asia High (SAH) in 40 years (1958—1997), the features of interannual and interdecadal variations as well as the period and period energy of the annual TC numbers are analyzed. Furthermore, the relationships between the annual TC numbers and the characteristic parameters of SAH are depicted, and the features of the SAH circulation and the 100 hPa height field in prior time in TC abnormal years are also composed and discussed. The results show that the TC numbers in Northwest Pacific have obvious interannual and interdecadal variations, and that the SAH in prior time has a certain influence on the TC frequency in a year. When the center of the SAH goes more westward and northward, and its center intensity is weaker, the TC numbers in the year would be more, and vice versa.
RELATIONSHIP OF OLR AND DEVELOPMENTOF TROPICAL CYCLONE OVER SOUTH CHINA SEA
Luo Qiuhong, Li Tianran, He Xiajiang
2004, 15(1): 81-87.
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Abstract:
The relationship of OLR and the development of tropical cyclones over the South China Sea is studied by using the OLR data (1990—2000). The results show that there is a good relationship between the development of South China Sea tropical depression and the OLR variation over the South China Sea. Tropical depression would easily develop into tropical storm when OLR low center embedded in ITCZ. Under the state of binary typhoons, the development of South China Sea tropical depression depended on the strength and distances of two OLR low centers. IOD (Index of development) was defined to describe the relationship between the variation of OLR and the development of South China Sea tropical depression quantitatively. Tropical depression would easily develop into tropical storm when IOD≥9.
STANDARDIZATION OF THE SOFT DESIGN FOR UPPER-AIR OBSERVATION
Yao Wen, Zheng Guoguang, Guo Yatian, Huang Bingxun, Du Bingyu
2004, 15(1): 88-94.
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Abstract:
The upper-air observation is one of the foundations of meteorological operation. The synoptic rawinsonde observing program is designed for the real-time operational needs for weather analysis and forecasts, and provides data of upper-air observations for the purposes of the research and climatological applications, and international exchanges. The developed course of the data processing system for the new sounding system is described. The request for the soft system and ideas for the design are emphasized. The significance for the application is illustrated.
DOPPLER RADAR DATA' S FOUR DIMENSIONAL VARIATIONAL ASSIMILATION
Yang Yanrong, Li Bai, Zhang Peiyuan
2004, 15(1): 95-110.
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Abstract:
The four-dimensional variational assimilation of Doppler-radar data (4DVAR) in theory was analyzed. Its main course and basic ideas were discussed. Then the four-dimensional variational Dopple radar analysis system (4D-VDRAS) was emphasized, the cost function was defined, and conjugate formulate and simile adjoint were applied to educe its minimum. In addition, radar disposing and Barnes insert technique were introduced. The application of 4D-VDRAS was discussed.
A SIMPLE ALGORITHM FOR DEALIASING VELOCITY AMBIGUITY
Liu Shuyuan, Wang Hong qing, Tao Zuyu, Liu Haixia
2004, 15(1): 111-116.
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Abstract:
Doppler velocity aliasing will appear when the radial component of the target’s velocity is greater than the Nyquist velocity of the radar. A simple and effective algorithm for Doppler velocity dealiasing is put forward based on the characteristics that the wind field is continuous along a ring centered at the radar and an unfolding Doppler velocity-azimuth profile always has a maximal away-speed and a maximal toward-speed. This new algorithm does not require the knowledge of an auxiliary wind field and manual judgement about aliased area. So, the assumptions for finding aliasing points are avoided. It does not need the help of auxiliary wind information and manmade judgment about aliasing velocities. It can be carried out easily and automatically by computer and has potential to be implemented in operational environment. The dealiasing algorithm has two steps for each PPI scan. The first step is to make the piecewise folded velocity-azimuth curve to be a continuous curve. The second step is to determine whether the continuous velocity-azimuth curve is on the correct level based on the character that an unfolded velocity-azimuth curve always has a maximal awayspeed and a maximal toward-speed approximately equal value. If not, the velocity-azimuth curve should be adjusted to the correct level according to the number n, which n = INT ((Vrmax-Vrmin)/ Vrmax). Where Vrmax is the maximum value and Vrmin is the minimum value in the velocity-azimuth curve. After the second step, the velocity-azimuth curve will be adjusted to the reasonable velocity interval. For get better result of dealiasing, the above steps can be repeated one or two times. The Doppler velocity data with multi-aliasing collected from Typhoon OTTO observed by Ludao Doppler Radar at the southeastern Taiwan on 4th August in 1998 is used to test this dealiasing algorithm. The result shows that this algorithm can effectively dealias multiple folds of Doppler velocities ones the low signal to noise ratio data have been thresholded.
RADAR OBSERVATION AND ANALYSIS OF MESO-SCALE VORTEX
Zhu Xiaoyan, Xue Qiufang
2004, 15(1): 117-125.
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Abstract:
Using single Doppler weather radar about the radial velocity information, a simple method for estimating the divergence and vorticity is presented. The vortexes are analyzed by this method in Beijing-Tianjin-Hebei area. The result indicates that the formation of the strong meso-scale weather system is related to turn or convergence and divergence of wind filed. The vorticity cyclone is a signature recognition of heavy rain and very useful for the cumulus convection.
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