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91.
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珠江三角洲城市群对夏季降雨影响的初步研究 总被引:5,自引:4,他引:1
利用TRMM 2A25卫星降水数据和CMORPH同化数据对珠三角洲地区的降水分布特征进行了探讨,观测表明:珠三角城市群区域总体处于降水的低值中心,且对流降雨的低值中心尤为明显;同时近10 a珠三角核心城市区域降雨有减少的趋势,这种降水减少的趋势可能与珠三角城市化效应有关。本文进一步利用WRF模式模拟分析了珠三角城市群发展对夏季降雨的影响,结果表明珠三角城市化使得该区域降雨减少,其原因为城市化使得地表的蒸发减弱及其大气中的水分供应减少,同时也抬升了珠三角区域边界层高度相应增强了低层大气水汽垂直混合。 相似文献
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Stephane C. Alfaro Valentina Flores‐Aqueveque Gilles Foret Sandrine Caquineau Gabriel Vargas Jose A. Rutllant 《地球表面变化过程与地形》2011,36(7):923-932
As previously observed in marine sediments collected downwind of African or South American continental sources, recent studies of sediment cores collected at the bottom of Mejillones Bay in north Chile (23°S) show a laminated structure in which the amount of particles of aeolian origin and their size create significant differences between the layers. This suggests inter‐annual to inter‐decadal variations in the strength of the local southerly winds responsible for (1) the erosion of the adjacent hyperarid surface of the Mejillones Pampa, and (2) the subsequent transport of the eroded particles towards the bay. A simple model accounting for the vertical uptake, transport, and deposition of the particles initially set into motion by wind at the surface of the pampa is proposed. This model, which could be adapted to other locations, assumes that the initial rate of (vertical) uptake is proportional to the (horizontal) saltation flux quantified by means of White's equation, that particles are lifted to a height (H), increasing with the magnitude of turbulence, and that sedimentation progressively removes the coarsest particles from the air column as it moves towards the bay. In this model, the proportionality constant (A) linking the vertical flux of particles with the horizontal flux, and the injection height (H) control the magnitude and size distribution of the deposition flux in the bay. Their values are determined using the wind speed measured over the pampa and the size distribution of particles collected in sediment traps deployed in the bay as constraints. After calibration, the model is used to assess the sensitivity of the deposition flux to the wind intensity variations. The possibility of performing such quantitative studies is necessary for interpreting precisely the variability of the aeolian material in the sediment cores collected at the bottom of Mejillones Bay. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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To describe temporal change in tafone development, an S‐shaped curve equation is proposed: Z = Zc [1 ? (n + 1) exp (? β t ) + n exp (? (1 + 1/n) β t )] , where Z is observed tafone depth, Zc is ultimate tafone depth, t is time, and n and β are constants. The applicability of this model is examined using tafone data selected from seven sites, which are categorized into three different salt‐weathering environments: a spray/splash‐dominant (occasionally wave‐affected) supra‐tidal zone, aerosol‐affected coastal regions, and inland desert areas. The results indicate that the equation can well describe tafone development in each of these environments. An investigation based on the values of n and β, determined through a best fit of the equation to the data, suggests that n characterizes site‐specific environmental conditions and β reflects the magnitude of factors controlling the recession mechanism of tafone surfaces. It is found that (1) the maximum rate of tafone growth dramatically decreases from supra‐tidal, through coastal, to desert environments, and (2) the growing mode of tafoni is different depending on the environmental settings. The erosional force to facilitate the development of tafoni at supra‐tidal sites is estimated to be about 400 times greater than that in the general coastal area. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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1955—2007年拉萨市雨季夜雨率变化特征 总被引:1,自引:0,他引:1
利用1955—2007年拉萨市逐日降水和气温地面观测资料,分析了拉萨市雨季(5—9月)夜雨率变化特征。结果表明:拉萨市整个雨季日夜雨率变化是比较稳定的,近50多年来基本没有发生明显的年代际变化。夜雨率与日降水量有显著关联,当日降水量在25 mm以下时,夜雨率随降水量增加而增大,当日降水量〈1 mm时夜雨率最小为75.2%,当日降水量为25 mm时,夜雨率达到最大值93.4%;夜雨率与日温差存在显著的负相关;拉萨多夜雨与地形有关,高夜雨率既有有利的一面,也会带来一些负面影响。因此,深入探讨夜雨率是制定有效防御气象灾害对策的重要依据。 相似文献
100.
Based on the 1951–2007 thunderstorms in Jiangsu, a study is conducted for their climate trends, periodicity, spatiotemporal patterns, and the distributions of the first and last days of the thunderstorms at different guarantee rates (GRs) using climate tendency rate, wavelet analysis, and GR for diagnosis. Results suggest that the inter-annual number of thunderstorm days (TSDs) exhibits a decreasing trend in this province. The trend is displayed mainly in the decreasing TSD number in summer and autumn except in spring, when the variation is not significant in the study period. In this province, the TSD number declines by ~2 days per 10 years. On an inter-annual basis, the pronounced positive departures of the number take place chiefly in the early 1960s, the late 1960s to the early-mid-1970s, the late 1980s, and the late 1990s compared with the negative anomalies dominant in the late 1970s to the mid-1980s, the mid-to-late-1990s, and the late 1990s to 2007. There are vast differences in the initial and ending days at diverse GRs in different areas of the province. At 50% GR, the earliest (last) days occur from mid-March to early April (early to late September) while at 80% GR, the initial (last) days are from late March to early May (early to late October). For the distribution of periods, the periods >8–10 years are relatively stable for the entire province. Based on 1951–2007 period analysis, the region north (south) of the Huaihe River experiences TSDs less (more) than normal days in recent years. 相似文献