Vol.19, NO.5, 2008

Display Method:
Spatial/Temporal Variations and Trends of Aerosol Optical Depth at 380 nm Wavelength in China During 1980—2001
Hu Ting, Sun Zhaobo, Zhang Haidong
2008, 19(5): 513-521.
Study is undertaken of the spatial and temporal distributions and long-term trends of 380 nm Aerosol optical depth (AOD) over China of 1980—2001 TOMS/NASA monthly data which are then treated with techniques such as EOF (empirical orthogonal function), Morlet wavelet transform, Fourier power spectrum, linear trend, Mann-Kendall test (M-K test) and moving t-test. The conclusions as follows are drawn. AOD differs greatly in its meridional distribution all over China. On an annual-mean basis there are two AOD high-value regions covering wide areas and active throughout the whole year, which are the basins in South Xinjiang and Sichuan Basin, together with a short-term high-valued area in South China as well as low AOD covering Northeast China and the Tibetan Plateau. In spring, the northern values are higher in comparison with the southern ones except the high value zone in South China. In summer the southern values are slightly bigger than the northern ones and the reversal happens in winter. AOD in autumn is higher in the north than in the south to the west of 110°N and v.v. to the east. During the research period, the AOD at wavelength of 380 nm varies remarkably with time, thickest during spring in most part of China except the Tibetan Plateau and thinnest in different seasons for regions all over China. Furthermore, variations in seasonal AOD are dominated by significant geographic characteristics, which are of two patterns. The one for summer is a type with the south/west AOD opposite to north/east AOD and the other is a type with no difference in the general tendency throughout the whole country for the other three seasons. Eleven areas (Zone A—K) are selected for regional research of the spatial and temporal variations based on the annual distribution and seasonal EOF analysis of the AOD characteristics. There are five kinds of annual cycles for the AOD in the selected eleven regions. The differences among seasons are decreasing with the latitude and significant in lower latitudes. AOD in target areas and the national means show pronounced intra-seasonal/annual oscillations, as well as significant 1-, 2- and 4-yearly periods. The AOD anomaly of China and regional representatives have been weakened since late 1980s. During 1980—2001 annual-mean AODs experience the linear increasing trends on the national and regional scales, whose increase rates have been slowed down since the period from the late 1980s to the early 1990s, occurring from east to west and from north to south in China, with remarkable inter-annual abrupt changes in North China, i.e., Zone A-F, H and K in this study. Except the decreasing trend in January, most of the regional trends in different study months also have similar linear increasing trends and decreasing shifts. The turning points of seasonal AODs in eleven selected areas also occur during the period from the late 1980s to the early 1990s, especially significant in time series of spring and autumn AODs for the eleven research zones.
Variations of East Asian Monsoon and Its Relationships with Land-sea Temperature Difference in Recent 40 Years
Yang Ming, Xu Haiming, Li Weiliang, Liu Yu
2008, 19(5): 522-530.
Using the NCEP/NCAR reanalysis grid data for the period of 1957—2000, East Asian Monsoon indexes defined by Qiao Yunting are calculated with interrelationship and annual changes of the indexes are examined. Relationships between the indexes and the variability of the weather elements and characteristics of the climate change in the east of China are analyzed by using surface data from 194 surface stations. The results show that the changes of the southwest monsoon, the southeast monsoon and the north monsoon are different. The intensity of southwest monsoon has been weakening until 1990s as well as the area's change. The southeast monsoon becomes weaker in recent 40 years. On the contrary, its range increases. The north monsoon changes little both in the intensity and area in winter. However the summer monsoon affecting the China continent weakens in liner changes in recent 40 years. In summer, the precipitation of Yangtze-Huaihe River valley increases apparently and decreases over the other east parts of China in summer. The precipitation of every part in monsoon region and its corresponding land-sea temperature difference show negative correlation, and the precipitation of Northeast China and North China have positive correlation with the land-sea temperature difference of Yangtze-Huaihe River valley. It means that when the land-sea temperature difference of Yangtze-Huaihe River valley drops, the precipitation of Yangtze-Huaihe River valley increases and that of Northeast China and North China decreases. The relationship between land-sea temperature difference and precipitation in two different phases are examined, and it is found that the influence of land-sea temperature difference on precipitation in summer enhances in the second phase (1979—2000) than in the first phase (1957—1978). The temperatures of the east part of China continent and the corresponding sea increase in recent 40 years, and the increasing velocity of the sea is larger than that of the continent, which resulting in the land-sea temperature difference decreasing year by year. That may be the cause why the summer monsoon changes weakly. During the period from 1957 to 1978, the temperatures of 850 hPa in summer drop over the middle and west part of China except north part of Xinjiang and rise over the east of China. During the second period from 1979 to 2000, the temperature of 850 hPa in summer rises all over China except middle and north part of Xingjiang and Qinghai, the north part of Gansu and west part of Inner Mongolia. The area where temperature of 850 hPa in summer increases most greatly moves from southwest of Northern China and east part of Yangtze-Huaihe River valley to west part of Yangtze-Huaihe River valley and the southeast sea to China continent.
Econometric Analysis on Beijing Temperature Influence upon Electricity Load
Wu Xiangyang, Zhang Haidong
2008, 19(5): 531-538.
The variation of electricity load is influenced by the weather, especially the temperature. Relationship model between them is established by using of econometrics method, and its predictive power is assessed by forecasting a monthly and a quarterly load.The mean daily temperature from Beijing Weather Observatory and daily maximum electricity load from Beijing Electricity Company during 2002—2004 are collected to form the model. Because of the temperature's nonlinear affect on load, the heating degree days (HDD) and the cooling degree days (CDD), which are the derivation index of temperature, are used as explanatory variables to establish a concise linear model. Degree days index is defined analogically as the accumulated Celsius degrees between a threshold temperature and the daily mean temperature. The HDD is a good estimation of an accumulated cold during the cold season and the CDD estimates an accumulated warmth during the warm season. The 18 ℃ threshold temperature is chosen in Beijing.The development trend, the different influence on load of different month, different day (holiday and workday), as well as the lag-effect on load of HDD and CDD are fully considered in the model. The errors autoregressive structure is introduced. The test results and actual data have a good fitting degree, R2 is up to 95%, and DW is 2.The CDD has a stronger influence on electricity load than the HDD. If the CDD increases 1 ℃, the electricity load will increase 3%; the HDD increases 1 ℃, the load will only increase 0. 4%. CDD's lag-effect is also stronger than HDD's. The electricity load on holidays, such as Saturdays, Sundays, the May Day holiday and the National Day, is 3%—4% lower than workdays, in the Spring Festival, it is even lower. Assessment of its predictive power shows that it works good for the medium prediction of electricity load, systematic errors of seasonal forecasting is 5. 4% at 99. 7% confidence level.
Satellite Microwave Retrieval Test for Non-precipitating Cloud Liquid Water in Henan Area
Peng Liang, Yao Zhanyu
2008, 19(5): 539-546.
The detection of cloud liquid water (CLW) is very important in current meteorological service and research. The precipitation process is influenced by the interaction between CLW, vapor and ice phase particles, so the changes of global climate and local weather are influenced by the distribution of CLW. The detection of CLW can be used to identify the artificial precipitation enhancement potential regions, so the efficiency of weather modification can be improved. The liable data needed in numerical weather prediction can be obtained by the detection of CLW, and the study of numerical prediction model can be validated by the observational results of CLW. Now, the application of satellite detection can be used for monitoring the large scale and whole process of the CLW.The TRMM Microwave Imager (TMI) 85.5 GHz channel vertical polarization brightness temperature and the vertical atmospheric properties (including temperature, pressure and humidity) contained in 4 times daily 1°×1°NCEP data are used to calculate the surface emissivity in Henan Province (31.4°—36.0°N, 110.4°—116.0°E) on March 6, 2005, by means of a numerical step-by-step method with VDISORT. The surface emissivity is supposed to be unaltered in short time. The emissivity of test area on March 21 is considered to be the same with the emissivity on March 21. The cloud top height is calculated with the TRMM/VIRS 12.0 μm channel infrared radiation data, and the cloud bottom height is supposed to be the local lifting condensation level calculated with the terperature and dew point temperature. The retrieved cloud is suppose to be vertically uniform distribution, then the CLW is retrieved by means of iteration method with TRMM Microwave Imager (TMI) 85.5 GHz channel vertical polarization brightness temperature and NCEP data. The calculated surface emissivity is evaluated with the Henan map, and the retrieved CLW is compared with the CLW data from TRMM 2A12 products in the same time and the CLW data from NCEP data, infrared cloud picture in the same period. The retrieved CLW is coincident with the distribution of cloud in infrared cloud picture, and shows improvements comparing with the CLW data from TRMM 2A12 products, from which the data are probably related to the precipitation, so the range of CLW is more smaller than retrieved CLW and the valid data of CLW are too few. The CLW data from NCEP are not corresponding to either the retrieved CLW or the distribution of cloud in infrared cloud picture. The model simulation results show that the method is more accurate in retrieving high cloud CLW than low cloud. The error is increased by the use of NCEP data instead of sounding data in the CLW retrieving. So in the future the condensed sounding data should be used in CLW retrivel test. The comparative analysis is mostly qualitative for the lack of measurements, so the quantitative comparative analysis should be done more in the future study.
Short Sequence Adjusting Method of Automatic Station's Wind Energy Parameter
Wang Ting, Wu Xi, Jiang Zhihong, Huang Shicheng
2008, 19(5): 547-553.
With the reduced usage of the conventional energy and concerns of its environmental damage and air pollution if widely used, it becomes more and more important to exploit wind energy. In view of the sparse distribution of manual stations, it is necessary to add the data of automatic stations when assessing wind energy resources. However the time sequence of automatic stations is short, the short sequence adjusting method of wind speed and wind energy density by using the hourly wind speed data of automatic and manual stations in 2005 and manual stations during 1971—2000 of Jiangsu is discussed. According to the boundary layer meteorology the wind speed ratio between neighboring weather observation stations is affected by the turbulence intensity and the different roughness of land surface. The stronger the wind speed of manual station is, the smaller the ratio is. The wind of automatic station and neighboring manual station is affected much by geostrophic wind and it is less affected by turbulence. Using the inverse function to simulate the ratio in the same period, the correlativity between automatic station's wind speed and neighboring manual station's can be obtained easily. Then it is able to adjust the wind speed of automatic station in representative year according to the correlativity. The statistical connection with nearby stations is stable in the same period and in the same weather system. Therefore by using the statistical connection between average wind speed and wind energy density, the annual mean wind density is obtained in each representative year. The calculated results show that the average error percentage of annual average wind speed based on the short sequence adjusting method is 3.38%. Using the manual stations as hypothetical automatic stations to test the revised result on average climatic conditions, it is found that the average error percentage of annual average wind speed revision is 7.13%; the average error percentage of annual average wind energy density is 13.26%, and the maximal result is 21.98%, the minimal result is 4.46%. It is found that the short sequence adjusting method is effective in correcting the wind energy parameter. Finally after adding the corrected automatic stations' data, the distribution pattern of wind energy density in Jiangsu is obtained. The detailed wind energy distribution information is described by the distribution pattern especially over coastal and riverbank regions. It is better than the distribution pattern only with 67 manual stations. Scientific basis is provided by the results for the work of wind energy resources assessment.
Differences Between Automatic-observed and Manual-observed Surface Temperature
Liu Xiaoning, Ren Zhihua, Wang Ying
2008, 19(5): 554-563.
Based on the parallel comparison of original base stations during the transition from manual observation to automatic observation and the 0 centimeter temperature data from parallel observation of base stations in 2005 in China, the analyses are made on the differences between automatic-observed and manual-observed surface temperature data in time scales of day, month and year. The method of maximum likelihood ratio has been applied to test the homogeneity of the monthly values of 0 centimeter surface temperature. And the homogeneity of surface temperature affected by automatic observation is discussed. The results show that the daily mean value from automatic observation is 0.54 ℃ higher than that from manual observation in 0 centimeter surface temperature of China. The 0 centimeter surface temperature, 0 centimeter maximum and minimum surface temperature have annual comparison values over 0.0 ℃ with the percentage of 80.3%, 58.2%, 92.2%, respectively, and in most stations the automatic-observed annual mean value is higher than manual-observed one. The average daily value difference between auto and manual observation generally decreases gradually from north to south, and the average daily value varies the greatest in the north of Helongjiang Province and the north of Inner Mongolia to 45°N, and most areas in Xinjiang Autonomous Region. In all the time scales including day, month and year, the difference between automatic-observed and manual-observed temperature is greater in cold time period than warm time period, especially in the winter of the north. The main cause is that when there is snow covering the ground in winter, the surface temperature from automatic observation is the temperature under the snow, which obviously is higher than the temperature above snow from manual observation. If without the influence of snow cover, then there is no obvious difference between the two kinds of observation. The instrumental difference and the ground feature both contribute to the observational difference. The inhomogeneity test shows that the inhomogeneity from 0 centimeter surface temperature in the north area lies in the change of observation in automatic observing stations, while in the south, the change of observation does not exert much influence on the inhomogeneity of surface temperature. When there is snow cover in the north, 0 centimeter surface temperature from observation does not present the real situation, which should be taken into consideration while using the data.
Application of KNN to Wind Forecast Based on Clustering Synoptic Patterns
Chen Yuying, Liu Huanzhu, Chen Nan, Zeng Xiaoqing, Ma Jinren, Liu Qianqian, Ma Shaiyan
2008, 19(5): 564-572.
Based on the model identification and an analogue forecasting, a new approach based on Self-Organizing feature Map (SOM) and cross validation is constructed, which is called K-nearest neighbor nonparametric estimation bootstrap model (KNN). 500 hPa geopotential height and 700 hPa u, v wind field over Northwest China are analyzed by the model clusterings at first, then the optimal K combination is sought using cross validation aiming at past samples under different weather patterns. Forecasting identification value of each synoptic pattern is determined by K-data, according to historical record. When forecasting in real time, what kind of synoptic pattern is to be known first, then K-data of different time is used to compute the nearest neighbor of real forecasting predictor to historical material predictor. Finally forecasting conclusion is obtained by using the standard of forecasting identification value. In order to validate the effect on cluster synoptic pattern to KNN, T213 NWP products from 2003 to 2006 in winter half year and the data of daily maximum velocity in Ningxia are used to construct prediction models of daily maximum velocity≥6 m/s pattern in Ningxia under synoptic and non-synoptic patterns at one time, data from Jan to May in 2007 is used for forecast experiments. The forecast evaluation results show that although the probability of original sample is reduced when adding the Self-Organizing feature Map of KNN, more false alarms in forecasting are avoided, so that the effect of forecasting is improved in general, especially the forecasting effects of some synoptic patterns compared with those that aren't patterned. The result is that the forecasting information of Ningxia high wind can be reflected by improved KNN. What's worth pointing out is that, the number of synoptic patterns is reduced when patterned, so the forecasting will be effected to some extent. It has a good effect for meteorological observing station which has more original samples, but it is not good for the ones that have less original samples. Therefore if there are more historical data which can reflect the wide range of system changing, the forecast accuracy will be improved significantly and it has a great value for operational usage. Classification analogue prediction thinking can be expanded by these results.
Thermal Effects of Architecture Surface in Kunming and Beijing
zhang huining, Zhang Yiping, Peng Yunchuan, Zhou Yue, Peng Guifen
2008, 19(5): 573-581.
Urban architecture and the urban heat island intensity is extremely closely related. The buildings' outside surface exhibits unique thermal energy characteristic because it absorbs the solar radiation and thermal energy from people's daily life influences buildings. The atmospheric thermal energy condition around buildings is affected inevitably, then the urban climate is affected. The observational data of buildings' external walls' surface temperature, rooftop surface temperature and the air temperature near the buildings' external surfaces in three different cities of Kunming, Beijing utilized. The vertical distribution rule of buildings' external surface temperature and air temperature near the buildings' external surfaces, the thermal effect features of the wall, and the rooftop between the nearby atmosphere are analyzed. The comparative analysis on two cities buildings thermal conditions is conducted. The following preliminary conclusions are drawn. In the same area, buildings' external walls' surface temperature and the air temperature near the buildings' external surfaces are different respectively from different directions, seasons, and heights. The influence of solar radiation on buildings' external walls surface temperature is greater than on the air temperature near the buildings' external surfaces. Generally speaking, the wall's surface is a heat source in daytime, and a heat sink at night. In different areas, there are many similarities and many differences in the thermal energy affect on buildings' external walls. The heat flux of the buildings' external walls basically is positive in daytime, is negative at night, and there is an extreme small value just before sunrise in Kunming. While in summer of Beijing, the heat flux of the buildings' external walls is basically negative in daytime and positive at night. This indicates that the influence of climate and people's activity is great to the thermal energy effect on the urban buildings' external walls in different cities. The average heat fluxes between the buildings' rooftop and its nearby air are basically positive in different areas and seasons. Buildings' rooftop displays the strong heat source effect. The thermal energy effect intensity and the solar radiation show a positive correlation. In summary, the urban building external surfaces (external wall surfaces, the surface of rooftop) are different from the ground in the urban region, and is noticeably influential thermal active surface in the formation of urban climate.
A Long-term Atmospheric Temperature Dataset Derived from NOAA Microwave Sounding Unit with Cross-calibration
Zou Chengzhi, Gao Mei
2008, 19(5): 582-587.
The Microwave Sounding Unit(MSU)on board the National Oceanic and Atmospheric Administration(NOAA)polar-orbiting satellites measures the atmospheric temperature from the surface to the lower stratosphere under all weather conditions, excluding precipitation. These instruments are extensively used to determine the atmospheric temperature trend. However, calibration errors are a major source of uncertainties in the trend determination. Recently, NOAA/National Environmental Satellite, Data and Information Services has developed a non-linear sequential calibration method using simultaneous nadir overpass(SNO)to reduce calibration errors and then a long term MSU deep layer atmospheric temperature dataset is generated based on the new calibration. The dataset is introduced, which includes global 5-day averaged deep-layer temperatures for the mid-troposphere, tropopause, and lower-stratosphere with grid resolution of 2.5° latitude by 2.5° longitude. Also, the methodologies for the dataset generation are described, which including cross-calibration, incident angle correction, grid data generation, and bias correction in gridded data. The 20-year climate trends during 1987—2006 for the three layers are obtained from the dataset. Finally, the website for acquiring the dataset is provided.
Thermal Structure Characteristics of the Extratropical Transition of Tropical Cyclone Chaba(0417)
Zhong Yingmin, Xu Ming, Wang Yuan
2008, 19(5): 588-594.
The thermal structure characteristics of tropical cyclone(TC)Chaba(0417)over the western North Pacific Ocean in 2004 in its extratropical transition(ET)period are analyzed with the temperature data from NOAA-15 AMSU-A, reanalysis data from NCEP and black body temperature(TBB)data from GMS-5. It is found that the original symmetric structure of warm core is destroyed and sinking with slope asymmetric distribution in the ET process, and there is a weak warm center in the upper and lower troposphere respectively in the core region. The remarkable front characteristic in Chaba circulation appears distinctly. Through the thermal structure analysis, it is found that the extratropical cyclone is developing while Chaba is decaying. The decay of the tropical cyclone and the development of the extratropical cyclone occur successively while the tropical cyclone moves to the higher latitude area and interacts with preexisting mid-latitude system. The obstruction of water vapor transport and the symmetric warm core destruction are caused by the intrusion of cold air from middle upper troposphere in west semi-circle of Chaba. At the same time, a dipole is caused and advantaged conditions for extratropical cyclone development is initiated by the weak warm air which ascends cyclonically in the east semi-circle of the tropical cyclone and the cold dry air which descends in the west semi-circle of the tropical cyclone. Consequently, a sort of conceptual model of ET process in the Western North Pacific Ocean is proposed. The development of the extratropical cyclone is the result of the interaction between the warm air ascending in the east semi-circle of the TC and the cold air from mid-latitude in the west semi-circle of the TC.The beginning of the extratropical transition period of tropical cyclone Chaba in the Western North Pacific is defined while the tropical cyclone circulation encounters the preexisting mid-latitude baroclinic front zone and interacts with it. The end of the extratropical transition period of tropcical cyclone Chaba is defined while the original closed circulation of tropical cyclone enters completely into the westerly circulation in 500 hPa and evolves into a baroclinic storm, it indicates that tropical cyclone Chaba is captured by westerly circulation and an asymmetric distribution of clouds in the extratropical cyclone is remarkable.
Contrast Analysis on Numerical Simulation of 0703 Cyclone Strong Storm Surge
Yan Lifeng, Jiang Wensheng, Zhou Shuling, Jiang Shaocai
2008, 19(5): 595-601.
The coastal high water levels in Bohai Sea and the north of Yellow Sea result in a storm surge disaster onMar 4—5, 2007.The severe storm surge disaster is caused by the surface cyclone.Using T213 and NCEP data(1000 hPa wind and the surface pressure)by Hamburg Shelf Ocean Model, 0703 cyclone storm surge in BohaiSea and the north of Yellow Sea is simulated to investigate the process of storm surge set-up.The model is testedwith observations of Yantai and Weihai.The results show that the agreements between calculation and observation storm surge set-up of Yantai and Weihai are good, and the period of storm surge set-up in Bohai Sea and thenorth of Yellow Sea is well simulated.The numerical simulated results are in better agreement with observationsusing T213 than NCEP data.It indicates that it is feasible to study and simulate cyclone storm surge in BohaiSea and the north of Yellow Sea by Hamburg Shelf Ocean Model.
A Numerical Study on the Long-lasting Wide Spread Dense Fog Event During December 24—27, 2006
Zhou Mei, Yin Yan, Wang Weiwei
2008, 19(5): 602-610.
Fog presents a severe hazard in areas of intense traffic, such as airports and highways. Moreover, because air pollutants are not easy to be dispersed in foggy days, it is also harmful to human health and agricultural production. Fog prediction is essential to public safety and has a high economic value. To precisely predict foggy weather, it is essential to first understand the mechanisms responsible for fog formation and maintenance.The NCAR/PSU MM5 V37 is used to simulate and diagnose a dense fog event in Jiangsu Province and the surrounding areas during December 24—27, 2006. In the control simulation, the Gayno Seaman parameterization of the boundary layer is used. The deep convection parameterization of Grell is adopted, and the explicit treatment of warm rain is employed. To account for the important role that longwave and shortwane radiation play in fog formation, the cloud radiative scheme is employed. The center of the simulation area is set in Nanjing(32.03°N, 118.46°E). Two computational grids with horizontal grid distances of 30 and 10 km and domain sizes of 60×60 and 76×76 grid points are considered respectively in a two-way nesting method. High resolution in the boundary layer(another 9 levels joins below 200 m)is provided by thirty-two vertical levels, stretched monotonically from the surface to 100 hPa. Sensitivity experiments are performed to under stand the role of radiation. In the sensitivity tests, a series of simulations are performed with different radiative schemes, while keeping the others physic schemes fixed. The results show that longwave radiative cooling from the Earth's surface and the atmosphere are the most important factors for the formation and development of this fog event. Meanwhile, the steady atmospheric stratification and plenty moisture supply also play an important role. The fog dissipation is influenced mostly by the shortwave radiative heating and turbulent heat transfer after sunrise. During the development and maintenance stages of the fog, the surface layer is basically weak convergence region of water vapor, while in the weakening and dissipating period, the majority of the fog area is weak divergence region of water vapor. It indicates that the wide area of divergence descending accompanied with surface cooling and cold advection are the favorable conditions for the formation of a temperature inverse layer near the ground which is responsible for the maintenance of this prolonged fog event.
Thunderstorm Cloud-to-ground Lightning Characteristics in the Contiguous Guangzhou City and the Influences of Local Environmental Conditions
Meng Weiguang, Yi Yanming, Yang Zhaoli, Wan Qilin
2008, 19(5): 611-619.
The possibility of a relationship between thunderstorm and cloud-to-ground(CG)lightning activity suggeststhat the real-time lightning data provided by local lightning detectors may be useful in the nowcasting of some severe local thunderstorms.In fact, in recent years, increased interest in severe storms associated with lightninghas been led to by such potential application and the desire to understand the cloud electrification mechanisms responsible for the lightning behavior.In the current study, bsaed on available data sources such as CG flashrecords, radar detection data and conventional sounding data, the CG lightning properties of thunderstorms inthe contiguous Guangzhou city and the influences of local environmental conditions are explored.Based on theweather reports and the lightning activities, 10 lightning storms and 10 non-lightning storms are selected and divided into two groups to identify the CG lightning properties and favorable environmental conditions.In additionto general statistical analysis, sounding data from the nearby Qingyuan station are analyzed to identify systematicdifferences in the local mesoscale environment of lighting and non-lightning storms.And two typical lightningstorms are investigated to study the lightning behavior in severe and non-severe thunderstorms.It shows that over 90% negative polarity cloud-to-ground(CG)lightning is produced by most thunderstorms around Guangzhou city.During a 3-hour period surrounding the most lightning activity and calculatedwithin an analysis range of 150 km, of the ten selected storms with lightning records, the largest storm-averageflash density is 0.13 km-2·h-1, the maximum mean negative current is 28.4 kA, the peak current of the firststroke is 183 kA, and the largest multiplicity(the number of strokes per flash)is 14.CG flash rates are foundto be associated with storm intensity.Within the same system, when the storm develops stronger, it tends toproduce higher CG flash rates.When compared among different storms, however, the CG flash rates are quitedifferent.Stronger(weaker)storm does not necessarily mean that it produces higher(lower)CG flash rates.Bystudy of the differences of local environmental conditions between the two groups of selected lightning and nonlightning storms, at least, it can be inferred that storms with CG flash phenomena are supported in environmentwith stronger vertical wind shear, higher storm-relative helicity and convective inhibition(CIN). CG flash isproved more likelihood to occur in stronger convective systems with more organized features.Analysis of typicalcases reveals that urban environment may have possible impact on the evolution of thunderstorms and subsequentlightning activity.It is found that when moving thunderstorm approaches the urban areas of Guangzhou, its intensity and CG flash rates tend to decrease, and after it travels through the city, thunderstorm intensity andflash rates increase again.Testing with more observational case studies is needed for this primary result, andmore studies are necessary before general assumptions can be made regarding the typical thunderstorm lightningbehavior in this local area.
Winter Temperature Characteristics of Nanjing During 1951—2006
Miao Qilong, Xu Xiazhen, Pan Wenzhuo
2008, 19(5): 620-626.
Based on the daily temperature data during January 1951 to April 2007 in Nanjing, the change trends andcharacteristics of winter average temperature, annual extreme-low temperature, cold accumulated temperatureand low temperature days in Nanjing in the recent 56 years are analyzed and studied.The annual change of thewinter temperature and the distribution of warm winter and cold winter are discussed.The results show that theannual mean temperature tends to rise in the recent 56 years, and that winter average temperature also tends torise obviously as well as the winter lowest temperature and cold accumulated temperature tends to rise even moreremarkably.In recent 56 years, the average temperatures in November and December have no obvious change, at the same time the rising tendency of average temperature in January, February and March is very remarkable.The rise of temperature in winter is mainly contributed to by the rise of temperature in January, February andMarch, and that in November and December is slight.The obvious rise of winter temperature in recent 56 yearsis in accord with the global warming.The winters of 1950s and 1960s in Nanjing are low temperature periods, and the winter temperature tends to rise after 1970s.The phenomena of cold winter are all before 1980s, theydon't appear again till after 1990s.The phenomena of warm winter are very frequently observed after 1990s, and they appear once every two years.The winter temperature in Nanjing tends to rise more obviously after1980s, and the extraordinary phenomena of warm winter sustain after 1990s in Nanjing.The phenomenon ofbeing unusual warm in winter is more conspicuous in early several years in the 21st century.
Hail Distribution and Topographical Factors in Guizhou Province Based on GIS Technique
Wang Jin, Liu Liping
2008, 19(5): 627-634.
Research on the relationship of topographical factors to distribution of hail, and getting an image of subdivisions for hail hazard which quantificationally concerns the difference of topographical factors are important to hailweather forecasting.Also, best services for decision-making to disaster prevention and reduction is provided.The relationship between distribution of hail and some topographical factors, such as elevation, slope grade, slope aspect and terrain incision depth, are studied by using GIS techniques, such as digital terrain analysis, zonal statistics and image classification with historical hail records of 84 meteorological stations over 44 years inGuizhou Province and the 1:1000000 resolution DEM data of China.It shows that natural logarithm of meanannual hail days conforms to normal distribution.The elevation is the major topographical factor which primarilyinfluence the distribution of hail, the annual mean hail days increase with the increase of elevation and it increases remarkably as the elevation increases to about 1000—1500 meters.Micro topographical factors, such as slopegrade and slope aspect, are not remarkable factors to the variance of annual mean hail days, but topography rising over large area and windward slope of warm moist air are favorable to hail. Terrain incision depth is not remarkable factor to the difference of annual mean hail days either.Different latitude is also one of the factorswhich influence the difference of annual mean hail days.The model for annual mean hail days derived from thethree remarkable factors and the map of hail hazard evaluation are reliable via statistical test and comparison tohistorical hail reports over countryside spots.The analysis is influenced due to the lack of hail reports in inner mountainous area in Guizhou and the incomplete collection of hail reports data.The relationship between different topographical factors should be further studied.
Adjusting Methods of Earth Observation Field of FY-2 Meteorological Satellite
Qian Yun
2008, 19(5): 635-640.
As the most significant achievement of remote sensing detection for Earth surface and atmosphere, China'scapability of weather forecast, prevention from various kinds of weather disasters as well as environment protection is improved by geostationary meteorological satellites.FY-2 series is the first generation of Chinese geostationary meteorological satellites.It can be used for continuous real-time observation on the variation of weather over China and its surrounding area, and an importantrole is also played in accurate medium-and long-term weather forecast.FY-2D satellite is launched successfully in Dec 2006, and two geostationary meteorological satellites locatingwest and east over China are realized, their image dissemination coverage are very wide.The composite observation is not only extremely significant to China's weather forecast, hazard reduction, global climate change observation, but also meteorological service is provided to East Asia, South Asia and even Australia and part ofAfrica.China becomes one of the most important countries of meteorological satellite in the world.Geostationary satellite is only relatively still to the Earth.When FY-2 geostationary meteorological satelliteis located to operational position, observation area must be adjusted before their original image acquisition in order to target at Earth medially.Due to the action of Earth's rotation and other impetuses, the actual satellite orbit and attitude vary continuously, the raw images received may have shifts between east and west.The precision of framing could be influenced by the warp of scan radiometer of FY-2 meteorological satellites for the Earthobservation field.Therefore, once the Earth drifts away from the center of the satellite observation field, adjusting should be taken in order to control the scan radiometer aiming at the Earth.Therefore, it is part of the dailytask not only in the satellite original image acquisition period, but also frequently in its whole operational lifetime.Adjusting of observation field is done by sending several data-injected telecommands to the satellite fromthe ground station.A kind of self-correcting arithmetic is proposed by which the adjusting numbers and orientation for controlling scan radiometer can be calculated.That is to say that a result of the arithmetic can be used to choose data-injected telecommands and its pulse number instead of man-made decision.The data of arithmetic could be acquired by using the value of N, which comes from Synchronizer Data Buffer within CDAS(Commands and DataAcquisition Station)or using simulated telemetry data of FY-2 satellite.It is one of the software programs inSatellite Control Center correctly used for FY-2A and FY-2B when they are in normal operational mode and during their eclipse.It will be adopted to double satellites operational system to reduce satellite controlling manmade mistakes, to ensure security of satellites, to enhance its automatic operational abilities, and to increase thereliability of image obtained task of FY-2 meteorological satellite.