贵州鹅项水库沉积物特征及其土壤侵蚀的意义

对位于贵州西南部非喀斯特丘原区的鹅项水库中取得的一沉积物样芯（EX-1）做了¹³⁷Cs,TOC,C/N和粒度分析以及矿物磁性测量。通过对这些分析和测量结果进行解译,推测了在过去的45年（1960～2005年）中这一水库的汇水流域内土壤侵蚀强度的相对变化。在这45年中,鹅项水库流域的土壤侵蚀经历了由弱到强再持续减弱的一个过程。将这一推测结果与流域内降水数据和土地利用/覆被变化资料数据相结合,探究了该流域土壤侵蚀强度变化的原因。与贵州西南部典型喀斯特流域的情况相比,在鹅项流域内,土地利用/覆被变化情况对土壤侵蚀强度的影响相对次要,而降水对土壤侵蚀强度变化的影响则更为重要。这可能主要因为与典型喀斯特流域相比,鹅项流域的土层较厚、植被覆盖较好。     

Fast maximum likelihood estimation of signal parameters using theshape of the compressed likelihood function

A computationally efficient fast maximum-likelihood (FML) estimation scheme, which makes use of the shape of the surface of the compressed likelihood function (CLF), is proposed. The scheme uses only multiple one-dimensional searches oriented along appropriate ridges on the surface of the CLF. Simulations indicate that the performances of the proposed estimators match those of the corresponding maximum-likelihood estimators with very high probability. The approach is demonstrated by applying it to two different problems. The first problem involves the estimation of time of arrival and Doppler compression of a wideband hyperbolic frequency modulated (HFM) active sonar signal buried in reverberation. The second problem deals with estimating the frequencies of sinusoids. A threshold analysis of the proposed scheme is carried out to predict the signal-to-noise ratio (SNR) at which large estimation errors begin to occur, i.e., the threshold SNR, and its computational complexity is discussed     

Application of Radar Reflectivity Factor in Initializing Cloud-Resolving Mesoscale Model. Part Ⅱ: Numerical Simulation Experiments

Microphysics elements and vertical velocity retrieved were incorporated using the nudging method into the initial data assimilation of GRAPES (Global/Regional Assimilation and Prediction System) model.Simulation experiments indicated that nudging technique was effective in forcing the model forecast gradually consistent to the observations, yielding the thermodynamically and dynamically balanced analysis field. As viewed from the simulation results, water vapor is vital to precipitation, and it is a governing factor for the amount and duration of precipitation. The initial cloud water, rain water, and vertical velocity determine the strength distribution of convection and precipitation at the beginning time of forecast; the horizontal wind field steers the motion of the mesoscale weather system embedded in and impacts the position of precipitation zone to a large extent. The simulation experiments show that the influence of the initial retrieval data on prediction weakens with the increase of forecast time, and within the first hour of forecast, the retrieval data have an important impact on the evolution of the weather system, but its influence becomes trivial after the first three hours. Changing the nudging coefficient and the integral time-spacing of numerical model will bring some influences to the results. Herein only one radar reflectivity was used, the radar observations did not cover the whole model domain, and some empirical parameters were used in the retrieval method, therefore some differences still lie between simulation and observation to a certain extent, and further studies on several aspects are expected.     

近45年深层地温变化趋势分析

利用1961-2005年拉萨0.8 m,1.6 m和3.2 m逐月平均地温,采用气候倾向率、累积距平、信噪比等气候诊断方法,分析了近45年深层平均地温的变化趋势,以及异常、突变等气候特征.结果表明:近45年拉萨0.8 m和1.6 m年平均地温呈极显著的增温趋势,倾向率为(0.58～0.69℃)/10a;0.8 m和1.6 m平均地温倾向率春季最大,秋季最小;3.2 m平均地温却以夏季升幅最大,冬季最小;与同时期平均气温的增温幅度比较,地温增幅更大;20世纪60-90年代0.8 m和1.6 m年平均地温呈明显的逐年代升高趋势;季平均地温20世纪60-70年代均偏低,80年代大部分季节仍略偏低,90年代都表现为正距平;0.8 m,1.6 m和3.2 m年平均地温均在1999年出现了异常偏暖,异常偏冷现象仅发生在1.6 m土层上,时间为1963年;夏季深层平均地温异常偏暖均发生在1999年;冬季0.8 m 和1.6 m平均地温多异常偏冷年份,主要发生在20世纪60年代;1999,2002－2005年冬季3.2 m平均地温异常偏暖;夏、秋季平均地温的气候突变出现在1986年,冬、春季发生在1983年.     

近45年拉萨深层地温变化趋势分析

利用1961—2005年拉萨0.8 m, 1.6 m和3.2 m逐月平均地温, 采用气候倾向率、累积距平、信噪比等气候诊断方法, 分析了近45年拉萨深层平均地温的变化趋势, 以及异常、突变等气候特征。结果表明:近45年拉萨0.8 m和1.6 m年平均地温呈极显著的增温趋势, 倾向率为 (0.58~0.69 ℃)/10a;0.8 m和1.6 m平均地温倾向率春季最大, 秋季最小; 3.2 m平均地温却以夏季升幅最大, 冬季最小; 与同时期平均气温的增温幅度比较, 地温增幅更大; 20世纪60—90年代0.8 m和1.6 m年平均地温呈明显的逐年代升高趋势; 季平均地温20世纪60—70年代均偏低, 80年代大部分季节仍略偏低, 90年代都表现为正距平; 0.8 m, 1.6 m和3.2 m年平均地温均在1999年出现了异常偏暖, 异常偏冷现象仅发生在1.6 m土层上, 时间为1963年; 夏季深层平均地温异常偏暖均发生在1999年; 冬季0.8 m和1.6 m平均地温多异常偏冷年份, 主要发生在20世纪60年代; 1999, 2002—2005年冬季3.2 m平均地温异常偏暖; 夏、秋季和年平均地温的气候突变都出现在1986年, 冬、春季发生在1983年。     

Rock crevices determine woody and herbaceous plant cover in the karst critical zone

The study of the critical zones(CZs) of the Earth link the composition and function of aboveground vegetation with the characteristics of the rock layers, providing a new way to study how the unique rock and soil conditions in karst regions affect the aboveground vegetation. Based on survey results of the rocks, soils and vegetation in the dolomite and limestone distribution areas in the karst area of central Guizhou, it was found that woody plant cover increases linearly with the number of cracks with a width of more than 1 mm, while the cover of herbaceous plants shows the opposite trend(p0.01). The dolomite distribution area is characterized by undeveloped crevices, and the thickness of the soil layer is generally less than 20 cm, which is suitable for the distribution of herbaceous plants with shallow roots. Due to the development of crevices in the limestone distribution area, the soil is deeply distributed through the crevices for the deep roots of trees, which leads to a diversified species composition and a complicated structure in the aboveground vegetation. Based on moderate resolution imaging spectroradiometer(MODIS) remote sensing data from 2001 to 2010, the normalized differentiated vegetation index(NDVI) and annual net primary productivity(NPP) results for each phase of a 16-day interval further indicate that the NDVI of the limestone distribution area is significantly higher than that in the dolomite distribution area, but the average annual NPP is the opposite. The results of this paper indicate that in karst CZs, the lithology determines the structure and distribution of the soil, which further determines the cover of woody and herbaceous plants in the aboveground vegetation. Although the amount of soil in the limestone area may be less than that in the dolomite area, the developed crevice structure is more suitable for the growth of trees with deep roots, and the vegetation activity is strong. At present, the treatment of rocky desertification in karst regions needs to fully consider the rock-soilvegetation-air interactions in karst CZs and propose vegetation restoration measures suitable for different lithologies.     

湖泊(水库)沉积物分析在土壤侵蚀研究中的运用

土壤侵蚀研究对于防治自然灾害,实现土地的可持续利用具有重要的现实意义。由于一些地区长期以来水文观测资料较为匮乏,针对过去时间段内的土壤侵蚀研究通常需要寻找替代指标。湖泊(水库)作为流域内侵蚀产物的“汇”,其沉积物可不同程度地记录较长时期土壤侵蚀的具体特征,因此,基于湖泊(水库)沉积物分析的土壤侵蚀研究具有较强的应用价值和发展潜力。本文主要围绕确定土壤侵蚀年代,反演侵蚀过程,探寻沉积物来源的研究主线,详细论述了湖泊(水库)沉积物中放射性同位素、矿物磁性、粒度以及地球化学指标的应用原理和方法,分别总结了国内外学者利用湖泊(水库)沉积物在上述3个领域所取得的研究成果,在此基础上讨论了目前研究中存在的不确定性,并对未来的研究方向进行了展望。     

气候变暖背景下西藏地区工程施工气象条件分析

利用降水、气温、积雪、风和相对湿度等影响工程施工建设的气象要素综合定义了工程施工气象指数,根据其对工程施工影响程度分为5级;采用1980—2013年西藏地区38个气象站资料分析了西藏地区工程施工的气候条件特征,以及气候变化背景下西藏地区工程施工气象等级变化,结果表明：气温和降水是影响西藏工程建设气象等级的主要因素,6—9月是西藏地区适宜工程建设期;适宜施工日数自东南向西北减少,适宜施工期开始日自东南向西北推进,适宜施工期结束日自西北向东南推进,海拔越低,适宜施工日数越多、适宜施工期开始越早、适宜施工期结束越晚;随着气候变暖,西藏地区适宜施工日数增加,表现为适宜施工期开始日提前和适宜施工期结束日推迟。     

Indication of paleoecological evidence on the evolution of alpine vegetation productivity and soil erosion in central China since the mid-Holocene

Although alpine ecosystems have been commonly recognized as sensitive to recent climate change, few studies have examined its impact on the long-term productivity of vegetation and soil erosion. Using paleoecological records, these two aspects were examined in the alpine zone of the Taibai Mountains(elevation, 3767 m) in monsoon-dominated East Asia since the middle Holocene. Proxies for the productivity of vegetation and severity of soil erosion from high-resolution alpine lacustrine records show that the productivity and soil erosion were closely related to mean annual temperature and summer precipitation from the East Asian Summer Monsoon(EASM), respectively. Specifically, when the mean annual temperature was low and precipitation was abundant, during 5800–4000 calendar years before the present(cal. yr BP), the alpine ecosystem was characterized by low vegetation productivity and severe soil erosion. However, the productivity increased and soil erosion decreased from 4000 cal. yr BP onwards. These results highlight the role of paleoecological evidence in studying ecosystem services on longer time scales, which is significant in making policies for sustainable development under climate change in regions for which such long-term monitoring data are not available.     

近50年拉萨日照时数的变化特征

采用气候倾向率方法对拉萨1953～2005年的年、季节日照时数变化趋势分析表明,近50年来拉萨年日照时数和各季节日照时数都存在不同程度的减少趋势,年日照时数以每10年27.6h倾向率减少,且这种减少的趋势在增大,主要表现在夏、秋季。20世纪50～80年代年日照时数均为正距平,90年代以负距平为其主要的年际变化特征;90年代夏季日照明显偏少,60年代冬季日照充足。年日照时数90年代末出现异常偏少年,夏季日照时数仅在2000年出现了异常偏少现象,而冬季日照时数多异常年份,主要发生在50年代。年平均总云量减少趋势明显,低云量下降趋势显著。