排序方式: 共有93条查询结果,搜索用时 15 毫秒
81.
青藏高原地气耦合系统及其天气气候效应:第三次青藏高原大气科学试验 总被引:3,自引:0,他引:3
赵平 李跃清 郭学良 徐祥德 刘屹岷 唐世浩 肖文名 师春香 马耀明 余兴 刘辉志 假拉 谌芸 柳艳菊 李建 罗达标 曹云昌 郑向东 陈军明 肖安 远芳 陈东辉 潘旸 胡志群 张胜军 董立新 胡菊旸 韩帅 周秀骥 《气象学报》2018,76(6):833-860
由于青藏高原(简称高原)是影响中国极端天气和气候事件的关键区,对天气、气候预报有重要影响。因此,中国气象局、国家自然科学基金委员会、中国科学院共同推动了"第三次青藏高原大气科学试验(TIPEX-Ⅲ)"工作。自2013年的预试验开始,TIPEX-Ⅲ在高原西部狮泉河、改则和申扎新建全自动探空系统,填补了高原西部缺少常规探空站的空白;在高原中、西部建成土壤温、湿度观测网;实施了高原尺度和那曲区域尺度的边界层观测,那曲多型雷达和机载设备的云降水物理特征综合观测,高原多站的对流层-平流层大气成分观测。在研究成果方面,项目结果指出,在高原中、西部草原、草甸和裸土下垫面状况下地表热量湍流交换系数和感热通量明显低于过去较早的估计值;高原主体的对流云活动主要不是来自南亚季风区的向北传播,而可能是局地发展所致;揭示出那曲对流云日变化特征、云宏微观特征以及云中水不同相态之间的转化机制,提出了夏季高原加热在维持亚洲大气"水塔"中的作用,以及高原加热对亚洲、非洲、北美洲气候的调节作用。在数值预报模式中,Γ分布比M-P分布更适合于高原雨滴谱特征,通过改进高原热传导过程参数化方案可以降低模式中高估的地表感热,并提升模式对中国中、东部雨带的模拟能力;此外,考虑青藏高原关键区信号可以提升中国中、东部降水的预报技巧。TIPEX-Ⅲ还带动了地面和高空常规观测、天气业务雷达和风廓线雷达等观测数据加工处理业务技术的发展,提升了中国国家级土壤湿度、水汽含量等遥感产品和高分辨率多源降水融合产品的质量,促进了气象监测、预报和数据共享业务的发展。 相似文献
82.
83.
84.
黟县岩体位于江南造山带北东段,是该区侵入新元古代基底中面积最大的复式岩体。本文对黟县岩体开展岩浆岩锆石U-Pb年代学和全岩地球化学分析和研究。该岩体可划分为两个侵入体,岩石类型分别为闪长岩、花岗闪长岩。锆石U-Pb定年结果表明,闪长岩和花岗闪长岩的LA-ICP-MS锆石U-Pb年龄分别为812±19 Ma和150.6±3.3 Ma,即上述岩石分别形成于晋宁期和燕山期。花岗闪长岩的地球化学特征表现为钾质、钙碱性、过铝质岩石,具有类似埃达克岩特征:高SiO2(>65%),高Sr/Y(>21.44)和(La/Yb)N(>11.57)比值,高Al2O3(<16%),低MgO(<2.20%),低Yb(<1.36×10-6)和Y(<15.11×10-6),但贫钠(K2O/Na2O>0.5%)。闪长岩的地球化学特征表现为钾质、高钾钙碱性过铝质岩石,具有较高的Al2O3(>16%),MgO(> 2.39%)和高TiO2(> 0.41%)等含量,高Sr/Y(> 15.49)比值,低Yb(< 1.93×10-6)和Y(<15.5×10-6)含量,具有相似埃达克岩特征。两者的稀土元素配分图显示LREE富集,HREE亏损,强烈亏损P、Nb,具有微弱的Eu负异常。两者均为Ⅰ型花岗岩。两期岩浆源区主要源自古老下地壳岩石的部分熔融,晋宁期的闪长岩伴有地幔成分的参与。晋宁期的闪长岩可能形成于火山弧构造环境中,显示华夏地块向扬子地块俯冲汇聚过程;而燕山早期的花岗闪长岩形成于由挤压至拉张转换构造环境中,可能与古太平洋斜向俯冲作用有关。 相似文献
85.
86.
TANG Shihao ZHU Qijiang WANG Jindi ZHOU Yuyu & ZHAO Feng Research Center for Remote Sensing GIS Department of Geography Beijing Normal University Beijing China National Satellite Meteorological Center China Meteorological Administration Beijing China 《中国科学D辑(英文版)》2005,48(2):241-249
Vegetation index is a simple, effective and experiential measurement of terrestrial vegetation activity, and plays a very important role in qualitative and quantitative remote sensing. Aiming at shortages of current vegetation indices, and starting from the analysis of vegetation spectral characteristics, we put forward a new vegetation index, the three-band gradient difference vegetation index (TGDVI), and established algorithms to inverse crown cover fraction and leaf area index (LAI) from it. Theoretical analysis and model simulation show that TGDVI has high saturation point and the ability to remove the influence of background to some degree, and the explicit functional relation with crown cover fraction and LAI can be established. Moreover, study shows that TGDVI also has the ability to partly remove the influence of thin cloud. Experiment in the Shunyi District, Beijing, China shows that reasonable result can be reached using the vegetation index to retrieve LAI. We also theoretically analyzed the 相似文献
87.
88.
89.
The basic characteristics and spatial patterns of global cultivated land change since the 1980s 总被引:3,自引:1,他引:3
In this paper, we analyzed the spatial patterns of cultivated land change between 1982 and 2011 using global vector-based land use/land cover data. (1) Our analysis showed that the total global cultivated land area increased by 528.768×104 km2 with a rate of 7.920×104 km2/a, although this increasing trend was not significant. The global cultivated land increased fastest in the 1980s. Since the 1980s, the cultivated land area in North America, South America and Oceania increased by 170.854×104 km2, 107.890×104 km2, and 186.492×104 km2, respectively. In contrast, that in Asia, Europe and Africa decreased by 23.769×104 km2, 4.035×104 km2 and 86.76×104 km2, respectively. Furthermore, the cultivated land area in North America, South America and Oceania exhibited significant increasing trends of 7.236× 104 km2/a, 2.780×104 km2/a and 3.758×104 km2/a, respectively. On the other hand, that of Asia, Europe and Africa exhibited decreasing trend rates of–5.641×104 km2/a,–0.831×104 km2/a and–0.595×104 km2/a, respectively. Moreover, the decreasing trend in Asia was significant. (2) Since the 1980s, the increase in global cultivated lands was mainly due to converted grasslands and woodlands, which accounted for 53.536% and 26.148% of the total increase, respectively. The increase was found in southern and central Africa, eastern and northern Australia, southeastern South America, central US and Alaska, central Canada, western Russia, northern Finland and northern Mongolia. Among them, Botswana in southern Africa experienced an 80%–90% increase, making it the country with the highest increase worldwide. (3) Since the 1980s, the total area of cultivated lands converted to other types of land was 1071.946×104 km2. The reduction was mainly converted to grasslands and woodlands, which accounted for 57.482% and 36.000%, respectively. The reduction occurred mainly in southern Sudan in central Africa, southern and central US, southern Russia, and southern European countries including Bulgaria, Romania, Serbia and Hungary. The greatest reduction occurred in southern Africa with a 60% reduction. (4) The cultivated lands in all the continents analyzed exhibited a trend of expansion to high latitudes. Additionally, most countries displayed an expansion of newly increased cultivated lands and the reduction of the original cultivated lands. 相似文献
90.
黄河流域1961—2010年极端气温指数的时空变化特征 总被引:1,自引:0,他引:1
根据黄河流域67个气象观测站1961—2010年逐日气温资料,采用线性回归分析和M-K检验等方法,研究了黄河流域6个核心极端气温指数的时空变化特征。结果表明:1)黄河流域平均最高气温、平均最低气温、暖日阈值和冷夜阈值均呈现显著的上升趋势,上升速率分别为0.28℃/10a、0.37℃/10a、0.19℃/10a和0.60℃/10a;气温日较差呈现不显著的下降趋势,下降速率为0.08℃/10a;霜冻日数以3.36天/10a的速率呈现显著下降趋势。2)平均最高气温与平均最低气温(暖日阈值与冷夜阈值)的上升呈现明显的不对称性,这是引起气温日较差下降的主要原因,而黄河流域变暖和霜冻日数的减少主要是由平均最低气温的快速上升引起的。3)在空间上,黄河流域变暖趋势较为显著的区域为呼和浩特、乌拉特中旗、包头、惠农、鄂托克旗、东胜一带和绥德、离石、太原、太谷、延安、延长、隰县、吉县一带。4)黄河流域6个气温指数的年内变化以冬季最为明显,而且变化趋势显著,冬季变暖对黄河流域年内气温升高贡献最大。 相似文献