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81.
In 1982, the National Weather Service (NWS) published criteria for developing the spatial and temporal precipitation distribution characteristics of Probable Maximum Storms. The criteria, which are intended for use in the United States east of the 105th meridian, involve four variables: (1) location of the storm center, (2) storm-area size, (3) storm orientation, and (4) temporal arrangement of precipitation amounts. A computer program has been developed which applies the NWS criteria to produce hyetographs of spatially-averaged precipitation for a basin, or for each subbasin if the basin is subdividided. The basis and operational characteristics of the program are described, and an application is illustrated in which the program is used in conjunction with a precipitation-runoff simulation program (HEC-1) to compute a Probable Maximum Flood. 相似文献
82.
碳酸盐碳测定在沙尘暴来源地识别中的应用 总被引:7,自引:0,他引:7
根据中国大气颗粒物特点 ,在国内沙尘暴研究中首次尝试利用碳酸盐碳进行沙尘暴来源地识别。测定了一系列黄沙、大气颗粒物和沙尘暴源区土壤样品。初步了解了上述样品中碳酸盐碳含量情况 ,结合国外研究结果对影响北京的沙尘暴源区进行推测并与其他方法作了比较 相似文献
83.
84.
土壤水分对沙尘暴的阈值反应--以内蒙古中西部地区为例 总被引:6,自引:3,他引:6
以2001年4月至2003年6月内蒙古中西部地区逐时观测的土壤体积含水百分率资料为基础,论述了土壤体积含水百分率的时间变化规律及其对沙尘暴的阈值反应.得到的主要结论是:(1)土壤体积含水百分率有着单峰型日波动反应,最高和最低值分别出现在午后4时和午前9时.(2)土壤体积含水百分率的月际变化基本遵循以1a为周期作简单振动的变化规律,最低值出现在3~4月.土壤体积含水百分率全年波动介于18.5%~37.3%之间,年平均值为26.5%.(3)沙尘暴的发生在土壤体积含水百分率含量一定范围内并不随土壤含水量的降低而发生明显变化,但当土壤体积含水百分率低于19.5%时,则随着土壤体积含水百分率的降低而明显增加,表现为土壤体积含水百分率有明显的阈值反应.(4)引进沙尘暴时度的概念研究了沙尘暴发生的持续时间,由沙尘暴时度与土壤体积含水百分率的指数关系发现,在时度大于200min和小于120min的两类沙尘暴中,土壤体积含水百分率每降低1%,沙尘暴时度将分别增加19.94min和10.14min. 相似文献
85.
86.
Daizhou Zhang Guangyu Shi Yasunobu Iwasaka Min Hu Jiaye Zang 《Water, Air, & Soil Pollution: Focus》2005,5(3-6):261-276
Analysis of individual particles collected at Beijing in northern China revealed that particles abundant in calcium (Ca) always
constituted a large fraction of mineral particles in the urban atmosphere. The particles were characterized by cubic morphologies.
The major mineral element in the particles was Ca and few or no other mineral elements were detected. A large number of the
particles were in the range of diameter <1 μm, where common natural mineral particles were rarely detected. The contribution
of the Ca particles to the volume of total mineral particles greatly exceeded that of other mineral particles during non-dust-storm
periods and was comparable to that during dust-storm periods. Reagent film tests showed that particulate sulfate and nitrate
formation on the Ca particles was similar to that on common mineral particles. These results indicate that a large portion
of Ca in the atmospheric particulate matter in Beijing was from anthropogenic sources rather than from natural sources, and
the anthropogenic Ca particles acted as a significant medium for the formation of sulfate and nitrate. Similar particles were
also detected at Qingdao, a coastal city in northern China. Data of a dust storm event showed that Ca-abundant particles from
East China arrived there and moved out of the continent, similarly to Asian dust storm particles, suggesting possible contributions
of anthropogenic Ca even in Asian dust storm samples in the downstream areas. Therefore, Ca may not be a good indicator of
Asian dust from natural sources. However, the Ca particles, due to their unique shapes and elemental compositions, may provide
an indicator for the atmospheric dispersion of anthropogenic particulate matters in East Asia. 相似文献
87.
Wenshou Wei Hongfei Zhou Yuguang Shi Osamu Abe Kenji Kai 《Water, Air, & Soil Pollution: Focus》2005,5(3-6):207-216
The desert environmental changes in the source areas of dust storms occurring in Xinjiang are discussed based on the climate
changes and the impacts of human activities in Xinjiang during the past 50 years. The results show that the climate in Xinjiang
is changing from a warm-dry type to a warm-wet one. The warm-wet climate has been obvious since the mid-1970's, and especially
the sensitivity of the regional climate change in this arid area is obviously revealed by many factors, such as the characteristics
of the local climate change in south Xinjiang and north Xinjiang, the difference of climate change in the alpine zones and
the basins, and the change of areas of the waters bodies. Furthermore, these factors also reveal the difference in the regional
climate change between Xinjiang and central and eastern areas of China. The occurrence and development of dust storms are
directly affected by the precipitation, air humidity, status of underlying surface, etc. in the arid areas. The frequency
and intensity of dust storms are closely related to the natural conditions, changes of climate and desert environment, as
well as the dynamic conditions (i.e., weather systems) in the source areas of dust storms. Therefore, global warming is one
of the main causes resulting in the degradation of the ecological environment and the frequent occurrence of natural disasters,
especially the disasters of sand drift and dust storms in the arid areas since the late-1980's, which reveals that the inland
arid areas are sensitive regions to climate changes. 相似文献
88.
Meteorological characteristics and morphology of duststorms and other dust weather phenomena in the arid regions of East Asia
were described in order to investigate a possible role of mesoscale cloud disturbances that develop in synoptic-scale mid-latitude
cyclones in intensifying dust weather. This study is a statistical examination of conventional surface observational data
as well as satellite data obtained during April 2000–2003. In the deserts of Mongolia and northern China (e.g., the Gobi Desert)
duststorms and other weaker dust weather (i.e., dust whirls, blowing dust) frequently occur under a strong influence of synoptic-scale
cyclones; on the other hand in the Taklamakan Desert (northwestern China), dust weather phenomena occur in a less organized
fashion and may be driven mainly by local meteorological and geographical effects. A significant signal was identified, revealing
of the intensification of dust weather by the presence of convective cloud disturbances. Meteorological changes such as pressure
rise and temperature drop, typically found during the passage of cold fronts, were frequently observed in the cases of duststorms
occurring in the analysis region. However, no definite tendency was found for moisture change and wind speed in relation to
cloud activity, probably because rainfall amount is generally too low to moisten the boundary-layer air. 相似文献
89.
Scott A. Sheeder Jeremy D. Ross Toby N. Carlson 《Journal of the American Water Resources Association》2002,38(4):1027-1040
ABSTRACT: Many studies can be found in the literature pertaining to the effects of urbanization on surface runoff in small watersheds and the hydrologic response of undeveloped watersheds. However, an extensive literature review yielded few published studies that illustrate differing hydrologic responses from multiple source areas within a watershed. The concepts discussed here are not new, but the methods used provide a unique, basic procedure for investigating stormwater hydrology in topographically diverse basins. Six storm hydrographs from three small central Pennsylvania watersheds were analyzed for this paper; five are presented. Two important conclusions are deduced from this investigation. First, in all cases we found two distinct peaks in stream discharge, each representing different contributing areas to direct discharge with greatly differing curve numbers and lags representative of urban and rural source regions. Second, the direct discharge represents only a small fraction of the total drainage area with the urban peak becoming increasingly important with respect to the rural peak with the amount of urbanization and as the magnitude of the rain event decreases. 相似文献
90.