应用气象学报

Influences of Continental High on Inland Torrential Rain Associated with Severe Tropical Storm Bilis (0604)

Cheng Zhengquan, Chen Lianshou, Li Ying

2013, 24(3): 257-267.

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Abstract:
The remnant vortex of severe tropical storm Bilis (0604) endures over land for a few days, results in a large range of torrential rain over South China and leads to a calamity after it lands in Fujian Province on 14 July 2006. Many studies are carried out and reveal the crucial effect of low level southwesterly monsoon jet to the extreme rain event. But the influence of the continental high on the torrential rain is also worth being discussed. The analysis of circulation shows that during the torrential rain process associated with Bilis, the continental high at upper level strengthens, moves eastwards, and stretches downwards to the low level after Bilis makes landfall, which strengthens the northeasterly stream at the southeastern side of the continental high. When Bilis moves westwards, the northeasterly stream at the low and middle levels in the northwestern quadrant of Bilis, overlapping with that southeast to the continental high, is strengthened and increases the transfer of water vapor and instability energy to the inland, which is favorable to the maintenance of the remnant low and the typhoon trough. The vorticity above the inland rainstorm area remains high during the process. The budget shows that it is the long existing remnant vortex and typhoon trough whose intense convergence at the low level produces a large amount of vorticity, triggers the successive development of MCS and results in the continuous heavy rain. The contribution of the continental high is to help the maintenance of the remnant low and the typhoon trough, and to enlarge the horizontal advection of vorticity at the upper level. And a set of numerical sensitivity experiments reveals that, based on the background of strong southwestern monsoon, the intensification and eastward stretch of the continental high not only forces Bilis to move southwestwards, but also provides strong divergence at upper level over Bilis. Besides, the continental high influences the intensity and the distribution of heavy rain. The endurance of the remnant vortex and the typhoon trough, due to the strong low level southwesterly monsoon jet and the continental high, enhances the intensification of vorticity above the inland rainstorm area and the occurrence of torrential rain. And in the sensitivity experiment of weakened continental high, the northeasterly winds in the northwestern quadrant of Bilis become weakened and the transfer of water vapor to the inland rainstorm area and the vorticity decrease accordingly, which leads to the northward movement of rain bands and the decline of rain intensity with the decrease of the 24 h rainfall maximum in the inland by 1/3, compared with the control experiment.

Effects of Key Regional SST Inter-decadal Anomaly on Summer Precipitation in Eastern China

Yuan Jie, Wei Fengying, Gong Yuanfa, Chen Guanjun

2013, 24(3): 268-277.

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Abstract:
By the influence of the summer wind, the summer rain-band in Eastern China advances gradually from the south to the north in China, but under the influence of a variety of complicated factors, the rain-band propulsion speeds up or delays in a certain area, finally forms the different rain-band distribution types. First, four rain-band patterns are defined in summer precipitation in Eastern China and then four sea surface temperature (SST) modes which lead to summer precipitation anomaly are found using singular value decomposition (SVD) method, from which four key sea regions related significantly with summer rain-band patterns in Eastern China are selected, and characteristics of summer precipitation distribution in Eastern China and atmospheric circulation in East Asia are analyzed with composite analysis in the background of key sea regional winter sea surface temperature anomaly (SSTA) in terms of NOAA Twentieth Century reanalysis data, UKMO HADISST1 global monthly SST and monthly precipitation of 96 stations in Eastern China during 1931—2010.When the winter Kuroshio SST inter-decadal anomaly is positive phase, 500 hPa geopotential height field in summer shows that the blocking highs develop in the mid-high latitudes of Eurasia, the meridional circulation in westerlies are intensified, the cold forces are strong and the western Pacific subtropical high strengthens and shifts westwards. 850 hPa wind field anomaly in summer shows that the north of China is governed by anomalous anticyclone, over the South China Sea is southerly winds anomalies, and the East Asian summer monsoon is weak. The circulations are useful for Pattern Ⅲ in summer precipitation in Eastern China where the rain belt is located in the mid-lower reaches of the Yangtze. When the winter Southern Indian Ocean Dipole inter-decadal anomaly is positive phase, 500 hPa geopotential height field in summer shows that a positive anomaly distribution develops in the mid-high latitudes, the blocking highs develop, meridional circulation are intensified, cold forces are strong and the western Pacific high becomes strong and shifts southward and westwards. 850 hPa wind field anomaly in summer shows that north China is controlled by anti-cyclonic anomaly, the anomaly north airflow extends to Southern China region and the Somalia cross-equatorial flow strengthens, which bring more rainfall in the Southern China region.

The Climate Suitability Zoning Method of the Solar Greenhouse in the Northern of China

Zhang Mingjie, Zhao Yanxia

2013, 24(3): 278-286.

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Abstract:
With the mathematical statistical methods and consideration of the climatic condition requirements of solar greenhouse development, six factors which represent four aspects of light, temperature, wind and snow are chosen as the assessment indices based on the analysis of main climate factors related to solar greenhouse production in the northern of China. They are the total radiation in winter, the number of overcast days in solar greenhouse production season, the average temperature in winter, the annual extreme minimum temperature, the average monthly maximum wind velocity in production season and the average annual maximum snow depth. Then, using weighted index method, an integrated index model of climate suitability zoning is established. Index weights are determined by analytic hierarchy process. And last, a comprehensive climate zoning map of the solar greenhouse development is drawn out with GIS which divides the climatic suitability in this region into four grades: The most suitable, suitable, less suitable and unsuitable. In order to refine the zoning map, Ningxia and eastern Gansu, Henan, Shaanxi with different climatic characteristics in the study area are selected as three typical areas and more detailed climate suitability zoning are carried out, respectively. Results show that for differences of climate resources and their combination conditions, their effects on the development of solar greenhouse are different and weights of the same division index are distrinct in different areas. Fine zonings in typical areas can provide more practical guiding significance in greenhouse production run.In general, the zoning results are in line with the actual situation which proves the selection of index, the division of index threholds and the zoning method reasonable and feasible. At the same time, the quantitative description and complexicy of zoning indexes are realized by AHP and GIS tools. The zoning method not only has solid theory basis, but also is practical. Therefore, this attempt can provide an effective and reasonable way for future research. In addition, some development suggestions are discussed in accordance with the division results, providing reference basis for rationally utilizing climate resourses and adjusting the layout for solar greenhouse development reasonablly.

Assimilation of Observations with Crop Growth Model Based on the Constrained Analysis of Parameters

Sun Linli, Ma Yuping, Jing Yuanshu, E Youhao, Zou Yandong, Xing Kaiyu

2013, 24(3): 287-296.

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Abstract:
Data assimilation may support regional applications of crop growth model, in which the selection of parameters and initial value of variables need lots of optimizing. Constraint reflects the controllability of observations on model parameters or variable initial value. Optimization of constrained parameters will most likely reach optimal results in data assimilation. An assimilation method of observations and crop growth model is established based on constrained analysis of model parameters. Sensitive parameters and initial value of the state variables in crop growth models are first selected using sensitivity analysis based on optimization algorithms. Constrained parameters of different variables are then obtained through constrained analysis, which is defined according to the relation of goodness of fit (Q_T) and optimization results of parameters. The optimal value of each parameter is got by means of combinatorial optimization of constrained parameters at last. Based on the constrained analysis, observations of summer maize leaf area index (LAI) in North China can constrain initial total crop dry weight (T_DWI), initial specific leaf area (S_LA1), initial maximum leaf CO₂ assimilation rate (A_max1) and life span of leaves growing at 35 Celsius (S_PAN) in WOFOST under optimal soil water condition. Dry weight of living storage organs (WSO) with the same results as the LAI is achieved. Total above ground production (TAGP) still include specific leaf area between jointing stage and tasseling stage (S_LA2). Constrained parameters of LAI under water stress level include not only T_DWI, S_LA1, A_max1, and S_PAN, but also initial amount of available water in total root zone (W_AV), maximum daily increase in rooting depth (R_RI), and maximum initial and soil moisture content of the initial root depth (SMLIM). Parameters constrained by LAI, WSO, TAGP and soil moisture content (SM) are not exactly the same with each other. The values of crop and soil parameters and initial conditions in WOFOST are obtained using observations over North China in 2009. Simulation shows that WOFOST can reflect the process of summer maize development, growth, and yield formation. The assimilation approaches are the foundation for application of crop growth model at regional scale.

The Method to Determine the Noise Power of Wind Profile Radar

He Ping, Li Bai, Wu Lei, Gao Yuchun

2013, 24(3): 297-303.

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Abstract:
The main intention of designing wind profile radar is to obtain wind information of the atmosphere. However, it does not take full account of the function of intensity measurement. The applications of the wind profile radar will be greatly expanded, if the function of intensity measurement is implemented. A very important extension is to measure the process of precipitation and to get raindrop size distribution which can fundamentally improve the quality of quantitative measurement of precipitation. To achieve the intensity quantitative measurement, the key technical issue that must be solved is how to calculate the noise power accurately from power spectral density. Based on the power spectral density estimation method of wind profile radar adopted and the noise frequency domain statistical characteristics, a method to calculate noise power of wind profile radar is proposed and the validation of the method is done by using of wind profile radar measured power spectral density data. Results show that the method performs well. The power spectral density of noise can be separated accurately even in complex echo situation such as precipitation or strong surface clutter. The method is established on solid theory foundation. The calculation of noise power is accurately, quickly and efficiently, which looks forward to becoming a practical technology of wind profile radar.

Climatic Characteristics of Intense Snowfall in China with Its Variation

Liu Yulian, Ren Guoyu, Yu Hongmin, Kang Hengyuan

2013, 24(3): 304-313.

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Abstract:
Based on daily ground snowfall observations of national meteorological stations, climatic zonation is carried out according to the snowfall variability with the REOF method to the north of 25°N in China. The main climatic characteristics and variation of intense snowfall events in different climate zones are analyzed, including the spacial distribution difference, the changing characteristics of intense snowfall and the number of snow days of the month, ten-day, spatial changes and temporal evolutions in the trend of intense snowfall, the number of snow days and intensity, and the climate change trends of the 1961—2008 and 1981—2008 (considering climate warming) are calculated, respectively.It shows that the east of Tibet Plateau, Xinjiang and the north of Northeast China have the highest amount and frequency of intense snowfall. The maximum intense snow intensity centers in Yunnan. The percentage of intense snow days to total snowfall days is generally low in North China, followed by the north of Northeast China and Xinjiang, and the largest percentage occurs in the Huang-Huai River Areas. In the north of Northeast China, North China, Northwest China and the east of Tibet Plateau, the high-frequency periods of intense snow events are generally in spring and early winter. It comes to mid-winter in Xinjiang, and to late winter in the Huang-Huai River Areas. In the north of Northeast China, Xinjiang and the east of Tibet Plateau, the intense snowfall and snow days obviously increased over the last 48 years. With climate warming, the intense snowfall and snow days increase, and meanwhile the intense snow intensity strengthens in most regions of China.Due to the snowfall measurement error, the estimation results of the mean intense snowfall and snow intensity in the north of China may be low, in the spring, the mean wind speed is strong, and the intense snowfall and snow intensity estimation is lower. Because the wind speed near the ground is in decreasing trend, the analysis of climate change on intense snowfall and snow intensity may be that the increasing trend is overestimated, while the decreasing trend is underestimated. The snowfall measurement error change caused by the average wind speed decreasing mainly affects the analysis of intense snowfall events of climate change, while has few impacts on the research of climatic characteristics.

The Tropical Atmospheric Intra-seasonal Oscillation with Different Reanalysis Data

Ding Li, Li Qingquan, Liu Yunyun

2013, 24(3): 314-322.

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Abstract:
Characteristics of the tropical intra-seasonal oscillation are analyzed using three kinds of data (NCEP/NCAR reanalysis data, NCEP/DOE reanalysis data and ECMWF/ERA40 reanalysis data) in three climate states of 1961—1991, 1971—2000 and 1981—2010. There is a significant 30—60 d oscillation period of 200 hPa zonal wind in different climate states of different reanalysis data. Different intra-seasonal oscillation characteristics can be found in different data and in different climate states. It is found that in 1981—2010 climate state compared with the other two climate states (1971—2000 and 1981—2010), annual cycle characteristics of the tropical intra-seasonal oscillation are more pronounced, strong in winter-spring and weak in summer-autumn. The tropical intra-seasonal oscillation is stronger in the tropical Indian Ocean and the tropical western Pacific Ocean, also its active areas extend eastwards and become larger. The eastward propagating energy of the tropical intra-seasonal oscillation centers more in 1—3 waves, while the westward propagating energy becomes weaker. The tropical intra-seasonal oscillation starts northward propagating later. It propagates southward strongly which spreads to the Southern Hemisphere in the beginning of May. NCEP/NCAR reanalysis data and NCEP/DOE reanalysis data match well in the annual cycle characteristics of tropical intra-seasonal oscillation, intensity and energy propagation. While NCEP/NCAR reanalysis data and ERA40 reanalysis data have some distinctions: The tropical intra-seasonal oscillation periods center in 20—100 d and its peak value is 55 d of NCEP/NCAR reanalysis data, while its oscillation periods are 20—60 d and its peak value is 50 d of ERA40 reanalysis data. As to the periods of 80—100 d, the oscillation pattern of ERA40 reanalysis data is stronger than that of NCEP/DOE reanalysis data. The tropical intra-seasonal oscillation variance contribution proportion of NCEP/NCAR reanalysis data is a little less than that of ERA40 reanalysis data in the tropical Indian Ocean and the tropical western Pacific Ocean, while stronger than that of ERA40 reanalysis data in the Eastern Equatorial Pacific Ocean. From December to the middle of March, the tropical intra-seasonal oscillation intensity of ECMWF data is stronger than that of NCEP/NCAR reanalysis data. While from the middle of March to November, the tropical intra-seasonal oscillation intensity of ERA40 reanalysis data is weaker than that of NCEP/NCAR reanalysis data; the tropical intra-seasonal oscillation phase of ERA40 reanalysis data is about 10 days ahead of NCEP/NCAR reanalysis data. The eastward propagating energy of the tropical intra-seasonal oscillation of NCEP/NCAR reanalysis data is weaker than that of ERA40 reanalysis data, while the westward propagating energy is stronger than that of ERA40 reanalysis data. In the middle of July, the northward propagating of NCEP/NCAR data is weaker than that of ERA40 reanalysis data.

Cloud Base Height Measurement Methods Based on Dual-camera Stereovision

Tao Fa, Ma Shuqing, Qin Yong, Hu Shuzhen, Wen Xiangang, Lei Yong, Guo Wei, Zhang Chunbo

2013, 24(3): 323-331.

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Abstract:
A pair of digital cameras whose baseline length are 60 meters are used to constitute a binocular imaging cloud base height measurement system, which can be used in image acquisition, processing, calibration, the whole sky cloud image splicing, cloud high layer and calculation and data storage and terminal display, etc. Along with the digital camera technology and stereoscopic vision sensor development, binocular imaging visual sensor is widely used because of its simple structure, good usability and higher measuring accuracy. Through the laboratory calibration and field calibration for internal and external bearing elements, obtaining two cameras inside, outside elements and relative attitude angle, the measurement accuracy are improved. The CCD acquisition cloud image has some disadvantages such as poor texture and low signal-to-noise ratio, therefore, image enhancement and filtering pretreatment should be carried out to meet the image feature extraction and matching requirements. Through the method of histogram equalization to enhance the images, sub-pixel corner point detector are used to improve the measurement precision. The normalized cross-correlation method for regional correlation are adopted for same name point detection, which will be eliminated by introducing the polar constraint reference to image matching process.Then according to the matching feature points, getting relative parallax, height of cloud base can be calculated by use of photography measurement principle. The cameras are calibrated in lab for internal and external elements first, then calibrated using the star relative position and attitude angle of camera relationship on the spot, which ensures the measurement precision. In Beijing, with CL31 ceilometer for contrast test, concrete analysis are carried out to investigate the system error and possible causes for this cloud height measurement system.Binocular imaging cloud base high measuring methods is direct photogrammetry method, which has overcome the poor accuracy of passive remote sensing and improved the measuring accuracy. According to the analysis, the accuracy can be improved through improving camera resolution, calibrating the internal and external elements of camera, correcting relative attitude angles of the two cameras, and controlling sample synchronization time and so on.However, visible light image sensor is greatly influenced by light and obstruction, which is only suitable in a daylight and when the cloud image texture is clear. In order to reduce the influence of illumination and improve data acquisition rate, infrared image sensor can be used to constitute a binocular imaging cloud base high measuring system, to realize cloud base high measurement.

The Spatial and Temporal Variations of Weighted Mean Atmospheric Temperature and Its Models in China

Gong Shaoqi

2013, 24(3): 332-341.

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Abstract:
Atmospheric water vapor plays an important role in the high-energy thermodynamics of the atmosphere and the generation of storm systems. Water vapor remote sensing can provide a detailed primary parameter within meteorological prediction and climate models. Ground-based GPS can obtain continuously precipitable water vapor with high spatial and temporal resolution since regional GPS networks are established widely all over the globe. Weighted mean atmospheric temperature (T_m) is a key parameter in retrieval of atmospheric precipitable water vapor from ground-based GPS measurements, and the precision of P_W retrieved by ground-based GPS is proportional to the accuracy of estimated T_m. Using radiosonde data of 123 stations in China from 2008 to 2011, the relationship of T_m is analyzed with its affecting factors, latitude, altitude, surface temperature (T_s), partial pressure of water vapor (e) and atmospheric pressure (P₀). Results show that T_m has a negative periodic correlativity with latitude and altitude as season changes, it has a good positive correlativity with surface temperature and partial pressure of water vapor transformed by natural logarithm, and it also has a negative one with atmospheric pressure. Furthermore, the spatial and temporal variations of T_m is discovered. The spatial variation of T_m displays the distinct latitudinal and climatic features and its spatial heterogeneity is evidently different in different regions, so T_m in different latitudinal zone is dissimilarly affected by seasonal climate change. For the temporal variation, T_m displays the prominent inter-annual variation and its diurnal variation is accord with the quadratic function. Given that, the regression models of T_m based on single factor T_s multi-factor T_s, e and P₀ are deduced respectively corresponding to all areas in China, climatology divisions and seasonal divisions, and then these models are validated by radiosonde data from January to May in 2012. The results show that estimated T_m would achieve an uncertainty of 2% for precipitable water vaper retrieved from GPS measurements, and these models are suitable to estimate T_m for the retrieval from ground-based GPS measurements in China.

The Evaluation of SR-50 for Snow Depth Measurements at Tanggula Area

Xiao Yao, Zhao Lin, Li Ren, Jiao Keqin, Qiao Yongping, Yao Jimin

2013, 24(3): 342-348.

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Abstract:
Snow cover, an important component of the cryosphere, has a profound impact on the surface and atmospheric heat conditions, ecological environment and water resources due to its special characteristics such as high reflectivity, high emissivity and low thermal conductivity. Because of its altitude and topography, the Tibet Plateau becomes the largest region with snow cover in the Northern Hemisphere. Snow cover data commonly used in scientific research is mostly collected by satellite, microwave snow monitoring data or the daily snow depth measurements from meteorological observation stations. These data show a disadvantage of insufficient time resolution when studying the detailed processes of snow cover and the impacts.Ultrasonic snow depth sensor SR-50, developed by Campbell Company, is an advanced observation instrument for snow depth. Using the measurements obtained by SR-50 at Tanggula (TGL) comprehensive monitoring site in the permafrost region on the Tibet Plateau, the evaluation of SR-50 for snow depth measurements is introduced and the characteristics of snow cover in permafrost regions are analyzed.The results indicate that SR-50 shows a very good ability in monitoring the real-time snow depth on different time scales. SR-50 could capture the detailed processes of surface snow cover, and gain real-time snow depth data. The processes of snow falling and melting could be well understood through the varieties of snow depth. The data of snow cover have a very important role in the study of snow cover processes and its impacts on land surface processes in permafrost regions. It shows that surface snow cover appeared in each month throughout the year in the target regions on the Tibet Plateau. The snow covered days mainly concentrated in the winter half year. In February, March, October and November, the number of snow covered days is larger, but in June, July and August it is much smaller. Overall, the snow depth at TGL site is much thinner compared with that of high latitude regions, and the duration of snow cover is much shorter due to the faster melting speed brought by much higher solar radiation. From 2005 to 2008, the instantaneous maximum snow depth of the region is 22 cm and the days with mean daily snow depth below 5 cm accounts for 71.58% of all snow days. In addition, recent raingauge record of solid precipitation is generally much lower than the actual situation because wind and other factors affect its capturing rate. The observations of snow depth by SR-50 provide a valuable dataset for revising the solid precipitation on the Tibet Plateau.

The Relationship Between Snowfall and Snow Depth Using Intensive Snowfall Observations

Yang Kun, Xue Jianjun

2013, 24(3): 349-355.

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Abstract:
In China, snow disaster occurs frequently and covers a vast territory which can remarkably impact agriculture, traffic, people's life and many other aspects. The relationship between snowfall and snow depth is an important parameter for the snow forecasting and other related researches, which plays a role in snow disaster prevention and mitigation. And newly support is given with the starting of intensive snowfall observations since the winter of 2009. These new intensive snowfall observations during winters of 2009—2012 and the linear fit function of least absolute deviation method are used to analyze the relationship between snowfall and snow depth. Furthermore, the study is conducted on how it changes with conditions of different temperatures, time, regions and using other snow data.As a result, it is found that the ratio of snow depth increment to snowfall in China during winter is 0.75 cm·mm^-1 in general, which is consistent with the result that using the regular winter observational rainfall and snow depth data. And it also shows that the ratio of snow depth increment to snowfall would decrease apparently with air temperature rising for the impact of temperature conditions on the state of snowing. In addition, the relationship between snowfall and snow depth presents marked difference in different region on the basis of investigating eighteen provinces in China which cover most regions that may have snow in winter. This relation is relatively stable in different temperature conditions, which also reveals that the ratio of snow depth increment to snowfall would increase slightly when temperature drops in most regions. And the relationship shows no obvious temporal variation, but it can be found that the relationship in Northwest and Northeast China is stable but fluctuant in North China and the Huanghuai Area.A preliminary analysis about the relationship between snowfall and snow depth is conducted under different conditions, its result can be used as a reference for snow depth estimation and used in weather forecasting and decision-making support. Further discussion on new data is needed to obtain more accurate and reasonable parameters in practice. Moreover, the intensive snowfall observations provide new data for snow research, but they also have many limitations which can affect the final result. Since it is a common problem that the research on snow is restricted by lacking suitable snow data, more high quality snow observations will be needed to support further analysis in the future.

Quality Control of Cloud Derived Wind Vectors from Geostationary Meteorological Satellites with Its Application to Data Assimilation System

Xue Chenbin, Gong Jiandong, He Caifu, Wang Ruichun

2013, 24(3): 356-364.

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Abstract:
Cloud derived wind vectors can provide plenty of useful information for synoptic analysis and numerical weather prediction, because of their excellent spatial and temporal coverages. It is of great value to apply cloud derived wind vectors efficiently with the purpose of improving the initial fields and numerical forecasts. The quality control of cloud derived wind vectors from geostationary meteorological satellites has been one of the important and difficult problems to be solved in satellite data assimilation. It has a direct impact on the prediction level of numerical weather prediction model. On the basis of the statistical analysis of global cloud derived wind vectors for 14 months, the quality indicator threshold of the five channels of cloud derived wind vectors in tropics, north and south hemisphere extra-tropics in high, middle and low levels from five global geostationary meteorological satellites in business operation, is analyzed and calculated. The error characteristics of infrared, water vapor and visible channels in the space area of cloud derived wind vectors are investigated, and the corresponding QI thresholds are determined. On the basis of quality control and equal-distance thinning scheme, the vertical distribution characteristics of cloud derived wind vectors are analyzed. It shows that after quality control, the number of infrared channel accounts for the vast majority, water vapor channel follows, and visible light channel the least.Furthermore, the method of innovation vector and zero-order Bessel fitting function which is based on the theory of least square method are adopted together to partition background and observation error variances in the observation space, and thus estimate the observation error of cloud derived wind vectors and the quality control coefficient according to the statistical distribution of the innovation vectors. On this basis, in order to validate the assumption on uncorrelated observation errors required in three-dimensional variational method, observation errors are inflated to avoid the influence carried by correlated errors.Finally, three numerical simulation schemes are designed and the forecast improvement and impact of cloud derived wind vectors before and after quality control are analyzed. Results show that the cloud derived wind vectors after quality control can effectively reduce the error of analysis field at high level. And the global short-term and medium-term forecast ability can be improved obviously by assimilating cloud derived wind vectors after quality control. In particular, there is a clear improvement in forecast ability in terms of wind, geopotential height and temperature fields in tropics. The forecast improvement above high levels appears better than those of middle and low levels in northern and southern hemisphere extra-tropics.

Cloud Characteristics and Synoptic Background Associated with Severe Convective Storms

Cao Zhiqiang, Wang Xin

2013, 24(3): 365-372.

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Abstract:
Severe convective storms happened during 2005—2011 are analyzed and classified into four types based on cloud characteristics and synoptic background. Type Ⅰ locates within the cold air mass, Type Ⅱ is in the rear of westerly trough or cold vortex cloud systems, Type Ⅲ is in Meiyu front or shear line and Type Ⅳ is in the upper trough system which moves eastward from the Tibetan Plateau.Type Ⅰ usually happens in North China, the Huanghuai or Jianghuai areas. Hail, gale and tornados always arise from them. Before severe convective storms initiation, large scale cloud band of front or shear line always appears at the Jiangnan Area or South China. North of the large scale cloud band is the place where the severe convective storms will initiate, where the upper airflow is eastward or southeastward. Cumulus clusters or short troughs moving along the upper airflow are the key factor of the strong convection initiation.Type Ⅱ usually occurs at the east of China and the north of the Yangtze, and the main disaster is thunderstorm, hail and gale. When the water vapor content is plenty, heavy rainfall can also appear. The place where the severe convective storms will initiate is at the rear of the cloud band corresponding to the weather system. North of the cloud band, the anticyclone dry air intrusion is the main characteristics. Although there are weather systems both at the upper and lower altitude, the storms are still difficult to forecast.Type Ⅲ commonly happens during Meiyu period at the Jianghuai, Jiangnan areas or South China. The main disaster is heavy rainfall. There are some meso-scale convective systems imbedded in Meiyu front or shear line cloud band, maintaining for a long time. On water vapor channel image of satellite, the north border of the cloud band is usually trimly, which commonly go with the upper level jet. The south border of the cloud band is usually composed of feather style cirrus cloud. On cloud-derived wind field, the distance between the upper jet stream north of the cloud band and the upper anticyclone ridge is near.Type Ⅳ commonly happens at the east of Southwest China and the west of South China. The main disasters are torrential floods and mudslides. These severe convective storms usually happen at the northwest of subtropical anticyclone when the monsoon is active. The key factor that make them happen is the short trough moving from the Tibetan Plateau, which corresponds to a cloud band. Dark area or dark band after the cloud band can be seen on water vapor images.

Early Warning and Evaluating Impacts of Ice and Snow Disasters on Beijing Urban Transportation

Liu Yonghong, Hu Haibo, Fang Xiaoyi, Xie Pu

2013, 24(3): 373-379.

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Abstract:
Using urban historical damage data of ice and snow from 1952 to 2011, the snow damage grades to Beijing urban transportation operation is built for the assessment on the accuracy of the following ice and snow warning and evaluation model. Based on disaster science principal combining with historical damage data, warning and evaluation indices of ice and snow damage to Beijing urban transportation operation are selected which are time, ice and snow intensity, traffic vulnerability, warning ability and disaster reduction ability. Ice and snow intensity can be determined by snowfall, snow depth and air temperature. Traffic vulnerability is determined by road network density and its time evolution. Warning ablility is mainly determined by weather forecast quality and its information spreading ability. Disaster reduction ability can be estimated by the gross domestic product and its time evolution. From the sensitive of these factors to snow disaster, method of experts marking is applied to computing and grades division of the single related factor and the comprehensive indices. Using judging-matrix of analytic hierarchy process (AHP) method, weights of four comprehensive evaluation indices are computed. Weights of four indices are ice and snow intensity with 0.4404, traffic vulnerability with 0.2789, disaster reduction ability with 0.1797, time with 0.05264 and warning ability with 0.0484, respectively. And Beijing urban ice and snow disaster warning and evaluation model is also constructed using AHP method. Using the model, 38 samples of historical ice and snow disaster events in Beijing are evaluated. The total accuracy is 76% and the accuracy in recent ten years (2002—2011) is 89% which shows the model can simulate effectively the impact of ice and snow disaster on Beijing urban area. The analysis of index weights shows that the hazard factor is still the major factor but not the only determinant factor of urban ice and snow disaster, as the total contribution of the other four factors to snow disaster overtakes the contribution of hazard factor. The ice and snow intensity as hazard factor affects Beijing urban transportation operation together with other factors under urbanization process such as transportation and disaster emergency management. The analysis of assessment on historical snow disaster events shows that under the influence of other factors, even light snow is able to cause serious damage on urban transportation operation and heavy snow perhaps only has medium effects.

Effects of Urbanization on Human Comfort in the Yangtze River Delta

Han Wei, Su Jing, Wang Lin

2013, 24(3): 380-384.

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Abstract:
Assessment of urban human comfort is one of hot topics in the field of climate change. Due to rapid urbanization in developing countries, climate issues have gained increasing attention in cities. However, most of these studies are carried out in spatial and temporal variations of human comfort, few considers the effects of urbanization on human comfort. Therefore, the meteorological and urbanization data of Shanghai, Nanjing, Hangzhou and Hefei in the Yangtze River Delta are used to investigate the relationship between urbanization and human comfort, and determine the main urban factors on human comfort. First, the human comfort of four cities in the Yangtze River Delta during 1981—2010 is investigated, and the trends in cold or hot uncomfortable days of four cities are investigated, separately. The results show that Nanjing has the most uncomfortable cold days, while Hangzhou has the least, and Hangzhou has the most uncomfortable hot days while Nanjing has the least. There are downward trends in cold uncomfortable days, the decreasing tendency from large to small is Shanghai, Nanjing, Hangzhou and Hefei. There are upward trends in hot uncomfortable days, and the increasing tendency in descending order is Shanghai, Hangzhou, Nanjing and Hefei. Second, the levels of urbanization of four cities during 1991—2011 are analyzed by the fuzzy comprehensive evaluation, and the relationship between tendency of human comfort and the levels of urbanization are analyzed by the correlation method. The results show that there is a highly significant correlation between the levels of urbanization and the tendency rate of cold uncomfortable days, while no significant correlation is found between levels of urbanization and the tendency rate of hot uncomfortable days. Third, the urban factors on human comfort are investigated by gray relational analysis to determine main urban factors which affect human comfort. It is found that the main urban factor on human comfort is total population, while other more important factors are built-up area, total power consumption, public transportation vehicles, and capita green area.These results suggest that the urbanization of big cities reduce the number of cold uncomfortable days significantly. Urbanization, especially the factors of population increase, city expansion, and traffic congestion energy consumption have profound influences on human comfort of urban residents.

Vol.24, NO.3, 2013