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The structure of thunderstorm in the atmospheric boundary layer in Beijing area is analysed by using three-year data of tower. It is indicated that the outflow current of the thunderstorm in the lower layer is a sort of density current. An area of evident wind direction shear is found at about half an hour to one hour before the arrival of the gust front.The maximum intensity of the shear can reach 0.35sec-1.The inner structure within the density current is also very complicated. At the nocturnal stable boundary layer in summertime, the development of the convective motions is often triggered due to the instability of the Kelvin-Helmholtz wave. 相似文献
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湖南洞庭湖区土壤酸化及其对土壤质量的影响 总被引:24,自引:0,他引:24
酸雨沉降引起的土壤酸化是当前全球最大的环境问题之一,湖南洞庭湖地区是中国土壤酸化非常严重的地区之一。随着土壤的酸化,Cd和Pb等有害元素的水溶态和交换态含量上升,特别是土壤在碱性至弱酸性范围内,Cd的生物活性急剧提高,给农作物安全生产带来了危害。土壤酸化还造成K、Na、Ca、Mg等盐基离子大量淋失,有益元素有效态含量也急剧减少,土壤肥力下降,养分贫瘠,土壤质量下降。针对土壤酸化带来的种种影响,提出了建议:提高能源利用率;增施有机肥,提高土壤缓冲能力;改进施肥结构;适量施用石灰、白云石粉,调整土壤pH值。 相似文献
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CHARACTERISTICS OF TURBULENCE SPECTRA IN DIFFERENT WEATHER PROCESSES UNDER UNSTABLE CONDITIONS 下载免费PDF全文
In this paper,the data chosen from measurements by supersonic anemometers in Tongxian County of Beijing in1990 are used to study characteristics of turbulence spectra in precipitation weather.Some turbulence parameters such asturbulence intensity,heat and momentum fluxes,friction velocity,M-O length and stability parameter are calculatedand their dependence on turbulence spectra in different stability conditions are analyzed.Some encouraging results areobtained and compared with others' results. 相似文献
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前面我们介绍了主要几类云的识别方法,这些云在卫星云图上的分布有着不同的范围、形状和结构,这种大范围的云系分布常与一定的天气系统相联系。天气尺度的云系从外形上看,大致可分为带状云系、涡旋状云系以及细胞状云系。下面我们对这些云系及其有关的主要天气系统作一介绍。 带状云系 带状云系是指有一条明显的云带,它的宽度超过 相似文献
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随着工农业生产的发展,由重金属带来的土壤和农作物污染问题日益严重,农作物直接参与食物链循环,因此,重金属在农作物中的含量过高势必影响人类健康与生态安全,关于该问题已有报道[1]. 相似文献
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