浑善达克沙地沙丘剖面颜色变化的古气候意义   总被引：2，自引：0，他引：2  

付旭东  周广胜  张新时 《沉积学报》2016,34(1):70-78

为研究中国沙漠东部广泛分布的风成沙-古土壤沉积序列的颜色变化与古气候之间的可能联系,以浑善达克沙地为研究区,测定了7个天然风成沙-古土壤沉积序列的颜色(L*a* b*)、有机碳、总氮和粒度。结果表明:L*(亮度)、a*(红度)、b*(黄度)值分别介于32.41~65.89,2.73~7.52和-1.68~17.16;L*、a*、b*值之间存在正相关关系,其中L*和b*之间的相关性最显著(R2=0.90),而L*和a*之间的相关性最低(R2=0.26);L*、a*、b*值在垂直方向上具有相同的变化趋势和特征,它们在风成沙层位处为高值,在灰色-黑色砂质古土壤层位处为低值,但L*值变化较大,a*和b*值变化较小。均值的非参数检验表明L*可指示风成沙-古土壤沉积序列的风成沙和古土壤层的变化,而a*在这类沉积序列上变化不敏感。影响L*的主要因素与有机质含量和成壤作用有关,它们都与东亚夏季风强弱变化关系密切,因此L*有明确的古气候意义;L*低值对有机质含量增加和成壤作用的加强具有指示作用,是东亚夏季风增强的信号。基于颜色参数L*可以很好地重建中国沙漠东部风成沙-古土壤沉积序列的古气候变化。  相似文献   

数据质量聚类算法          下载免费PDF全文

李延  王大魁  耿晶  王树良 《武汉大学学报(信息科学版)》2019,44(1):153-158

在聚类算法中，聚类中心决定聚类的最终结果，而传统的分割聚类算法不能准确定位聚类中心。根据数据场提出了数据质量聚类中心的新概念，给出数据质量聚类算法，能够一次定位聚类中心，无需迭代，也无需预置聚类个数。7组对比实验表明，提出的方法能够准确定位聚类中心，获得良好的聚类结果和稳定性，优于传统的分割聚类算法和峰值密度聚类算法。  相似文献   

基于主应力旋转的黏性填土挡墙土压力          下载免费PDF全文

王恒利  邹正盛  刘京敏  王新宇 《水文地质工程地质》2021,48(4):64-71

填土水平墙背竖直光滑的挡墙,墙后土体处于以自重应力和水平应力为主应力的应力状态。实际工程中,挡墙背面与土体存在一定的摩擦及黏结力作用致使挡墙附近土体中的主应力发生偏转,此时,经典朗肯土压力理论不再适用。本文对挡墙附近土中的主应力状态进行旋转处理,通过分析墙后填土中应力状态摩尔圆,得到了考虑墙土摩擦和黏结力作用的黏性填土挡墙主被动土压力计算公式,分析了填土内摩擦角与墙土摩擦角对土压力的影响,使用算例将本文方法所得结果与现有黏性土土压力计算方法所得结果进行了对比分析。结果表明,朗肯土压力公式是本文所得计算公式的特例;随着墙土摩擦角和内摩擦角的增加,被动土压力逐渐加快增大;主动土压力随着内摩擦角的增加而减小;当内摩擦角较小时,主动土压力随着墙土摩擦角的增大不断减小,当内摩擦角较大时,主动土压力随着墙土摩擦角的增大先减小后增大;土内摩擦角的影响大于墙土摩擦的影响;相对于现有方法计算结果,本文方法所得主动土压力较大,被动土压力较小,墙土摩擦越大,2种方法所得结果的差值越大,土黏聚力还会加大这一差值。本文方法考虑了墙背土体主应力方向偏转的客观事实,所得计算结果将更符合实际情况。  相似文献   

基于水热因子的玉米物候模拟   总被引：3，自引：1，他引：2       下载免费PDF全文

李荣平  周广胜  刘景利  史奎桥  梁涛 《气象与环境学报》2009,25(3):19-23

对锦州14 a玉米各生育期特征及其与气候因子的关系分析表明：同品种玉米的物候期相近,变化在2 d左右,而吐丝期到成熟期所需天数变化较大,为6 d或以上;玉米各生育期的影响因子不同,气温与湿度对玉米出苗期、三叶期和七叶期的影响显著,播种期到七叶期的积温占整个生育期积温的20%,并与同期的空气湿度累积量显著二次曲线相关（R 2=0.91）。积温与空气湿度累积可较好地模拟玉米播种期至七叶期和玉米的总生育期。  相似文献   

非对称性增温对农业生态系统影响研究进展   总被引：9，自引：0，他引：9       下载免费PDF全文

谭凯炎  房世波  任三学  张新时 《应用气象学报》2009,20(5):634-641

该文概述了北半球和我国气候变暖中增温的非对称性特征:北半球气候变暖存在明显的季节差异和昼夜不同步性, 大部分地区冬、春季升温高于夏、秋季, 日最低气温升幅是日最高气温升幅的2~3倍; 近50年我国近地表气温升高主要是最低气温明显上升的结果, 日最低气温升幅是日最气高温升幅的2~3倍, 与北半球基本一致; 升温最显著的季节为冬季和春季。在此基础上概述了非对称性增温对农业生态系统的影响, 论述了非对称性增温对农作物物候和农作物产量的影响, 得出最低气温升高促使整个生长季延长, 促使早春作物物候期提前, 但最低气温和最高气温对不同作物的物候以及同一作物的不同发育阶段影响不同。现有研究多采用模型或统计的方法研究气候变暖对作物生长的影响, 认为温度升高对作物有“强迫成熟”效应; 而现有的最低气温升高和最高气温升高对作物生长影响的研究结果并不一致。非对称性增温对农作物影响的实验研究极少, 且缺乏对模型模拟结果的实验验证。  相似文献   

PALYNOLOGICAL RECORD OF PALEOVEGETATIONCHANGE DURING HOLOCENE AT NORTH TUMDPLAIN IN INNER MONGOLIA,CHINA   总被引：3，自引：0，他引：3  

王瑜  宋长青  孙湘君 《中国地理科学(英文版)》1999,9(1):87-91

I~are~orsruDVThemiddleinnerMongoliaissituatedintherearpartoftheeasternAsianmonsonzone,itissensitivetotheclimatechange,thereforeitsenvironmentchangeintheHOIOcenehasbeenPaidattentiontobythescholarsofpaleoclimateandpal~nvirorunent.Wedidhighr~lutionPOllenanalysisonapeatprofileinpluvialfan,whichwaslocated3kmtothenorthOfQaSq,theheadquarteroftheTumdBanner,InnerMongolia,withaltitudeof1000malerssealevel.Theaverageannualtemperaturewas5.6t,annualprecipitation300--450rum,theclimatewascontinentaland…  相似文献   

Comparison of water vapour,heat and energy exchanges over agricultural and wetland ecosystems     

Yijun Li  Li Zhou  Zhenzhu Xu  Guangsheng Zhou 《水文研究》2009,23(14):2069-2080

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Records of natural fire and climate history during the last three glacial-interglacial cycles around the South China Sea Charcoal record from the ODP 1144     

LUO Yunli  CHEN Huaicheng  WU Guoxuan  SUN Xiangjun 《中国科学D辑(英文版)》2001,44(10)

The history of natural fire and its relationship to climate during the last three gla cial-interglacial cycles in the Southern coast areas of China and the northern continental shelf of the South China Sea (SCS) are discussed based on the statistic study of charcoal particles and associated pollen data from ODP 1144 Site (20° 3′N, 117° 25′E, 2037 m in water depth). Accord ing to the results of the charcoal and pollen study, the sediments from the upper 225 m are divided into 8 zones (C1-8), which might be correlated with the Marine Isotope Stage 1-8 (MIS1-8)respectively. Our study indicates that during the last glacial period (MIS2, 4), the influx of charcoal particle was much higher than that from the interglacial period, suggesting strong occurrence of natural fire and dry climate. During MIS 6 and MIS 8 (C6, C8), although the influx of fine charcoal particles was quite high, the influx of the coarse and medium charcoal particle were much low,which might be due to the smaller source area of fire probably resulting from the limited exposure of the continental shelf before MIS5. During the interglacial period (MIS1, 5, 7), the influxes of charcoal particles were much lower, implying dropping of intensity of the natural fire and then a humid climate. Another reason is that the continental shelf was submerged into the sea during the interglacial periods, and the source areas of fire were reduced then. Although the influx of the fine charcoal particles was much lower during MIS3, the influx of the coarse and medium charcoal par ticles were almost equal to those of MIS4 (C4), which suggests that the intensity of the natural fire remained quite high and the climate was considerably dry during that period.  相似文献   

Forage Yield-Based Carbon Storage in Grasslands of China   总被引：7，自引：0，他引：7  

Jian Ni 《Climatic change》2004,67(2-3):237-246

Forage yield-based carbon storage in 18 grasslands of China was estimated according to the detailed investigation of grassland area and forage yield (standing crop), which were derived from a 10-year national grassland survey. The total forage yield carbon in Chinese grasslands is 134.09 Tg C for ca. 299 × 10⁶ ha of grassland area and 1232 kg/ha of mean forage yield. The carbon storage is different depending on grassland types and climatic regions. Meadow, steppe and tussock occupy 93.3% (125.14 Tg C), and desert and swamp only accounts for 6.7% (8.95 Tg C) of total forage yield carbon. Forage yield carbon is stored largely in temperate (38.4%, 51.54 Tg C) and alpine regions (30.4%, 40.78 Tg C), and to less extent in tropical regions (22.1%, 29.66 Tg C). These three regions take 91% of the forage yield carbon in grasslands of China. The warm-temperate region accounts for only 9% (12.1 Tg C) of forage yields carbon. The forage yield-based carbon in grasslands of China is more accurate than the site biomass-based carbon estimate and the carbon density-based estimate. Although, forage yield carbon storage is small compared with the total carbon storage in China, carbon budgets of grasslands are often a dominant component in many regions and provide an important management opportunity to enhance terrestrial carbon sinks in vast areas of China.  相似文献   

用群落调查及光谱观测数据的主成分分析方法研究草场各生物参数之间的关系   总被引：4，自引：0，他引：4  

张剑  李贵才  刘先华  韩兴国 《遥感学报》2005,9(6):725-732

以内蒙古锡林河流域典型草原为研究对象,在群落调查和光谱观测数据的基础上,引入主成分分析方法(PCA)研究了与草场健康有关的各生物参数间关系,提出一种草场健康状况监测的新方法:(1)从包含12个反映群落各方面信息的变量中提取出3个有特定生态学意义的主成分,并进一步对其进行分析组合,得出一个能比较敏感、全面反映群落健康状况的新指标—草场健康指数(GHI);其意义在于:它不仅可以反映草场的生物量信息,而且可以反映群落的结构组成信息。(2)从6波段的植被光谱反射数据中提取出2个主成分:可见光因子和红外光因子,它们可以较好反映植被信息。(3)表征群落总量、放牧退化的主成分和GHI与植被光谱反射值有相当的相关性,由此得到GHI与可见光、红外光因子的回归模型。此模型可利用植被光谱较好地反映草场健康状况。  相似文献