Vol.13, NO.3, 2002

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Structures of Meiyu Fronts in 1998
Zhang Xiaoling, Tao Shiyan, Zhang Qingyun
2002, 13(3): 257-268.
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Abstract:
A diagnostic study of the dynamic and thermodynamic structures of Meiyu fronts in 1—10 June, 12—28 June, and 20—30 July 1998 is presented. It is found that fronts affecting precipitation over South China in early summer have the same dynamic and thermodynamic structures as Meiyu fronts over the Yangtze River Basin. They have the same structural characteristics as tropical synoptic systems. The vertical dynamic and thermodynamic structure of Meiyu fronts has quasi-tropical characteristics, the transition between ITCZ and the extra-tropical front.
A Diagnostic Analysis of Activities of the Western Pacific Subtropical High During the Second Meiyu Period in 1998
Liao Yishan, Yang Jingan, Shen Tieyuan
2002, 13(3): 269-276.
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Abstract:
The relationship between atmospheric meridional circulation and activities of the Western Pacific Subtropical High during the second Meiyu period in 1998 over the Yangtze River is analyzed. The results show that the advance and retreat of the Western Pacific Subtropical High are closely connected with the variation of the meridional circulation. The northward jump of the Western Pacific Subtropical High is not directly caused by the northward movement of the descending branch of the counter-circulation, which is connected with the Western Pacific Subtropical High. The development of the deep ascending motion at the lower latitudes obstructs the maintaining of the Western Pacific Subtropical High in the lower latitudes. Whereas, the sudden southward movement of the counter-circulation at the middle latitudes is in favor of the buildup of the Western Pacific Subtropical High in the farther north latitudes. Then, the Western Pacific Subtropical High jumps northward abruptly. This is form of the re-adjustment of the meridional circulation that ends Meiyu in the Yangtze-Huai River Region. The Western Pacific Subtropical High moves northward or southward along with the connected counter-circulation while remaining steady. Before the Western Pacific Subtropical High retreats from north, a new counter-circulation originates near the tropopause. When the new counter-circulation moves south rapidly, the Western Pacific Subtropical High moves south along with it.
Role of Summer Monsoon in Anomalous Precipitation Patterns During 1997 Flooding Season
Sun Ying, Ding Yihui
2002, 13(3): 277-287.
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Abstract:
By means of daily precipitation data and T63 reanalyzed in 1997, the precipitation in China during the flooding season and East Asian summer monsoon activities are studied. The results show that the precipitation in South China was obviously more than that in North China. The eastern rainbelt stayed in the South and to the south of the Yangtz River for a long time. Corresponding to the anomalous precipitation patterns, the monsoon activities showed prominent anomalies. The northward propagation of summer monsoon was very weak. The monsoon was active mainly in the lower latitudes with the northernmost position being at 35°N, 10 degrees south as compared with normal years. The main variation mode was 25 days low frequency oscillation while 30—60 day oscillation was not prominent. After the onset of SCS monsoon, the main moisture transport sources of SCS obviously changed. The high value centers of moisture transportation and convergence stayed in lower latitudes for a long time, which was favorable to the rainbelt maintenance in South China. This situation was closely related to the monsoon wind fields. The anomalous activities of East Asian monsoon play an important role in the anomalous climate of China in the summer of 1997.
Estimates of Regional Evapotranspiration in Various Surfaces
Liu Jingmiao, Zhou Xiuji, Yu Jinhua, Ding Yuguo
2002, 13(3): 288-298.
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Abstract:
The Kotoda-Bortan (K-B) model, used for estimating evapotranspiration, is modified. The estimates of evapotranspoiration on various surfaces from the modified model are compared with those from the Kotaoda model, Advection-Aridity model, Eddy-Correlation and Bowen radio methods, based on the data collected in the Yangtze Delta Field Experiment (1999) and the Huaihe River Basin Energy and Water Cycle Experiment (HUBEX, 1998). The results show that the evapotranspiration estimates from the modified model are very close to those from the Eddy-Correlation and Bowen radio methods both for instantaneous and daily emtimations. The modified model has the following advantages: (1) the necessary input data are limited to those easily obtainable from routine meteorological observation, remote sensing technique and geographical information system; (2) it can be used to estimate evapotranspiration not only from arid and semi-surfaces, but also from wet and vegetated surfaces; (3) the results can be given as digitized square-grid maps. Using this model, we estimated evapotranspiration on various surfaces in the Yangtze Delta region (118° – 123° E, 28° – 33° N) in 1995, and the regional average of evapotranspiration is calculated by the weight mean method .
Impact of Changes in Radiation Parameterization on Model Medium-range and Monthly Forecasting
Shen Yuanfang, Yi Lan, Chen Yi, Hu Guoquan
2002, 13(3): 299-311.
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Abstract:
A comparison of two radiation parameterization schemes has been carried out in the T106 Medium-range NWP model and the National Climate Center’s climate model T63. The radiation scheme used for the control integration in the two models at present was the original ECMWF operational radiation scheme (OPE), and the new radiation scheme (NEW) was the version that became operational on May 2, 1989 in ECMWF. Results indicate that OPE overestimates the short-wave water absorptivity, which leads to too large short-wave atmospheric absorption and too small downward short-wave radiation at the surface; OPE also underestimates the long-wave radiative cooling and the outgoing long-wave radiation at the top of atmosphere (OLR). In NEW the radiative energy available at the surface and an overall cooling of the troposphere increase; large turbulent heat fluxes are generated; the convective activity is enhanced; and the precipitation clearly increases. The warm temperature bias in the stratosphere in OPE is corrected. The operational parallel statistical test indicates a more pronounced improvement to the medium-range forecast of 4—7 days.
Interpretation of the Nonhydrostatic Mesoscale NWP Products in Terms of Local Weather Phenomena and Air Pollution in Beijing Area
Wang Yingchun, Liu Feng hui, Zhang Xiaoling, Zhang Chaolin, Meng Yanjun, Tuo Ya, Liang Feng
2002, 13(3): 312-321.
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Abstract:
The statistical and dynamical methods are used to interpret the mesoscale NWP products produced by the Beijing Area Mesoscale NWP System (which has been developed under a joint project of the National Meteorological Center and the Beijing Meteorological Bureau) in terms of the local weather elements and air pollution. First, the Kalman filtering method is applied to the mesoscale NWP products, generating the 3 h interval wind, temperature, and the daily maximum /minimum temperature forecasts over nine automatic weather stations in the Beijing area. The results of verification indicate that the forecasts of wind and temperature with Kalman filtering are much better than direct model outputs. Second, a simple dynamical air pollution model is connected to the Mesoscale NWP system, making daily air pollution forecasts. For the SO2, NO2 and CO, the predicted pollution levels are correct on more than 65% days during summer, fall and winter; for RSP, the forecasts are right on more than 65% days during fall and winter, but only on 50% days during summer. Both methods have been put into operational use.
Climatic Variation of Rainfall and Wet Days in Zhejiang
Gu Junqiang, Shi Neng, Xue Genyuan
2002, 13(3): 322-329.
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Abstract:
Study is made of climatic variation of rainfall and rainy on a yearly, monthly and daily basis in terms of 1961–1999 data from 36 stations in Zhejiang Province. The results show that the annual rainfall increased but the number of wet days did not correspondingly increase. The number increased in July and August but decreased in the other months, and rainfall increased more obviously than the number of rainy days in July and August, leading to the fact that mean daily rainfall intensity was augmented. The decrease in the number of wet days occurred abruptly around 1978 and the number reduced greatly in September–December after the 1998s .
Method for Detecting Rain Cloud Structure with Wind Profilers
Ruan Zheng, Ge Runsheng, Wu Zhigen
2002, 13(3): 330-338.
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Abstract:
Wind profilers are used for detecting the wind distribution of the atmosphere. During precipitation, owing to the influence of the terminal velocity of raindrops, the temporal variation of the real vertical wind structure can not be obtained directly. As wind profiler and Doppler weather radar are based on the same Doppler pulse principles, through the radar meteorological equation, the vertical structure of precipitation echo intensity, the content of liquid water in clouds and the Doppler terminal velocity of raindrops can be acquired. At the same time the wind structure of the atmosphere can be obtained through correction by the Doppler terminal velocity of precipitation particales .
Discussion on Convective Cloud Precipitation in Summer Using Radar Echo Data
Chen Qiuping, Zeng Guangping, Feng Hongfang, Sui Ping, Zheng Shuzhen
2002, 13(3): 339-346.
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Abstract:
??By using “713” digitized radar, the formation, development and dissipation processes of 101 convective clouds have been observed from July to September 2001 in the Jianyang weather radar station. Through analyzing these data, the convective cloud precipitation mechanisms in summer are discussed. The results indicate that initial echoes of 89.2% convective and 77.8% multiple-cell convective clouds appear below the 0℃ level; when the echoes reach the ground, compared to convective cells, the major echoes of obviously more multiple-cell convective clouds would expand to the cold/warm zone. Because the echo intensity, scale, precipitation time of multiple-cell convective clouds are greater than the convective cells, they are key precipitation cloud systems in summer and important to artificial precipitation.
Preliminary Analysis of Lightning Characteristics in Shandong
Feng Guili, Chen Wenxuan, Liu Shijun, Li Qingcai
2002, 13(3): 347-355.
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Abstract:
From 1998 to 2000, the data about 142588 cloud-to-ground (CG) lightning flashes are collected by a five-station lightning detection and location network in Shandong Province. In order to reveal the climatic characteristics, these data are used to study the daily variation, spatial density, intensity and polarity of lightning. The results show that major cloud-to-ground flashes are negative. The ratio of positive flashes with larger or smaller intensity to total positive flashes is bigger than that of negative flashes. The mean intensity of positive CG flashes is bigger than that of the negatives. The CG flashes occur clearly with a characteristic of daily variation, in which there are two peaks and two valleys. Furthermore, the spatial distribution of lightning is closely related to the topography and the nature of the underlying surface. The statistical analysis of some cities’ lightning density shows that Jining, Laiwu, Binzhou, Taian and Jinan, which are located in the middle Shandong Province, Should pay more attention to flash strikes.
Shanghai Heat Wave/Health Warning System
Tan Jianguo, Yin Hebao, Lin Songbai, L .S .Kalkstein, Huang Jiaxin, Shao Demin
2002, 13(3): 356-363.
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Abstract:
The Shanghai heat wave/health warning system is introduced. The Spatial Synoptic Classification (SSC) is used as the methodology for determination of the air mass classification using the daily meteorological observation data (1989–1998) in the system, and the ten-year-long air mass calendars is established. Through the comparative analysis of the daily air masses and their corresponding mortality, the MT+-pattern air mass is identified as the “offensive” air mass, which is related with the high mortality in heat wave periods in Shanghai. The equation was also produced for the prediction of excessive death by step-wise regression. The system test with actual meteorological data and mortality data in 1999 indicates that the Shanghai Heat/Health warning system has the good capability of warning excessive heat-related deaths .
A Diagnostic Experiment and Study of the Influence of O3 on Pakchoi
Bai Yueming, Wang Chunyi, Liu Ling, Guo Jianping, Wen Min
2002, 13(3): 364-370.
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Abstract:
A long time experiment on pakchoi in five O3 concentration treatments is made by using the OTC-1 open top chamber. The results show that lower O3 concentrations (25×10 –9 ~ 40×10 –9 and 50×10 –9) have chronic injury to pakchoi. When O3 concentration is up to 100×10 –9 or 200×10 –9, green pakchoi leaves faded and lost water. Increasing O3 content in ambient air may lead to shorter plant height and smaller plant pattern as well as the decreased leaf number, leaf area, photosynthesis rate, biological yield and economy yield. In addition, the experiment shows that pakchoi mesophyll and epidermis was influenced first when pakchoi in normal growing condition moved into the chamber with the O3 concentration being 100×10 –9 or 200×10 –9, but the veins of new leaves in the clamber twised and changed form first .
OLR Distribution in Summer in Dryness/wetness Years over Tibetan Plateau
Jia La, Zhou Shunwu
2002, 13(3): 371-376.
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Abstract:
Based on the OLR data observed by NOAA satellite, the climatic features of the radiation over the Tibetan Plateau and adjacent areas are investigated. The main results are as follows: the Plateau acts as the heat sink of the surface heating fields in winter and OLR is low; the Plateau rainfall mainly concentrates in summer and OLR is also low. There exists significant negative correlation between OLR over the Plateau and Plateau precipitation in summer; The change of OLR during the onset of Indian Monsoon reflects the adjustment of the Northern Hemisphere general circulation as well as the spatial and temporal pattern of thermal conditions over the Plateau during wet season. Composite India Ocean OLR anomalies patterns for five wet (dry) years over the Tibetan plateau in summer are studied. It is found that convection on the west and east of the Indian Ocean is abnormal obviously. Correlation analysis shows that OLR over the Bay of Bengal during spring has better negative relationship with rain over the Plateau in summer.
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