共查询到20条相似文献，搜索用时 343 毫秒
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Ann Henderson-Sellers 《Climatic change》1991,19(1-2):135-137
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Thomas Van Der Hammen 《Climatic change》1991,19(1-2):37-47
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Defining desertification: A review 总被引：5，自引：0，他引：5
Michel M. Verstraete 《Climatic change》1986,9(1-2):5-18
The concept of desertification was introduced in the late forties to designate a number of ecological degradation processes in tropical Africa, in particular the progressive transformation of tropical forests in savannahs or even drier ecosystems. Since then, the word has received a number of other meanings, some of them contradictory, most of them ambiguous.This paper reviews the historical developments that lead to the introduction of the concept of desertification, summarizes some of the reasons why this issue is so controversial, and suggests specific elements that should be incorporated in the definition of the concept. The point is made that each user of the concept should probably design a definition for his or her own use, depending on the goals, among other things.The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research and sponsored by the National Science Foundation. 相似文献
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《Atmospheric Science Letters》2000,1(2):101-107
To assist model intercomparison and development of a set of eight numerical experiments is proposed as a test-bed for the interaction of dynamics and physical parameterizations in atmospheric GCMs. The framework for the experiments is that of an aqua-planet and the prescribed sea-surface temperatures (SSTs) are highly idealized. 相似文献
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The Water vapour Strong Lines at 183 GHz (183-WSL) fast retrieval method retrieves rain rates and classifies precipitation types for applications in nowcasting and weather monitoring. The retrieval scheme consists of two fast algorithms, over land and over ocean, that use the water vapour absorption lines at 183.31 GHz corresponding to the channels 3 (183.31 ± 1 GHz), 4 (183.31 ± 3 GHz) and 5 (183.31 ± 7 GHz) of the Advanced Microwave Sounding Unit module B (AMSU-B) and of the Microwave Humidity Sounder (MHS) flying on NOAA-15-18 and Metop-A satellite series, respectively.The method retrieves rain rates by exploiting the extinction of radiation due to rain drops following four subsequent steps. After ingesting the satellite data stream, the window channels at 89 and 150 GHz are used to compute scattering-based thresholds and the 183-WSLW module for rainfall area discrimination and precipitation type classification as stratiform or convective on the basis of the thresholds calculated for land/mixed and sea surfaces. The thresholds are based on the brightness temperature difference Δwin = TB89 ? TB150 and are different over land (L) and over sea (S): cloud droplets and water vapour (Δwin < 3 K L; Δwin < 0 K S), stratiform rain (3 K < Δwin < 10 K L; 0 K < Δwin < 10 K S), and convective rain (Δwin > 10 K L and S). The thresholds, initially empirically derived from observations, are corroborated by the simulations of the RTTOV radiative transfer model applied to 20000 ECMWF atmospheric profiles at midlatitudes and the use of data from the Nimrod radar network. A snow cover mask and a digital elevation model are used to eliminate false rain area attribution, especially over elevated terrain. A probability of detection logistic function is also applied in the transition region from no-rain to rain adjacent to the clouds to ensure continuity of the rainfall field. Finally, the last step is dedicated to the rain rate retrieval with the modules 183-WSLS (stratiform) and 183WSLC (convective), and the module 183-WSL for total rainfall intensity derivation.A comparison with rainfall retrievals from the Goddard Profiling (GPROF) TRMM 2A12 algorithm is done with good results on a stratiform and hurricane case studies. A comparison is also conducted with the MSG-based Precipitation Index (PI) and the Scattering Index (SI) for a convective-stratiform event showing good agreement with the 183-WSLC retrieval. A complete validation of the product is the subject of Part II of the paper. 相似文献
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Alec H. Paul 《大气与海洋》2013,51(1):66-70
Abstract The frequency of tornadoes on the Canadian Prairies is a subject of much current debate. The author questions the traditional view that tornado frequency on the Prairies decreases westwards from southern Manitoba. A study of various sources of information on severe thunderstorm events on both sides of the 49th parallel leads to the conclusion that prairie tornadoes often are not isolated singular cases but rather are members of tornado outbreaks. Tornadoes in the northern Great Plains and Prairies are more frequent than has previously been thought, and are likely to be under‐reported compared with those of “tornado alley” in the United States. The Prairie Region can validly be regarded as an outlying section of the North American tornado belt. 相似文献