Bankfull Discharge Recurrence Interval in Gravel-bed Rivers     

F. Petit  A. Pauquet 《地球表面变化过程与地形》1997,22(7):685-693

Bankfull discharge was identified in some 30 gravel-bed rivers representing in total c. 40 gauging stations. The catchment sizes cary from 4km² to nearly 2700km². Bankfull discharge value increases with basin size. In the case of gravel-bed rivers developed on an impermeable substratum, the following equation emerges: Q_b=0·087 A^1·044. Bankfull discharge recurrence interval was determined by fitting maximum annual floods (T_a) into Gumbel's distribution and then using the partial duration series (T_p) in this same distribution. Recurrence interval is below 0·7 years (T_p) for small pebble-bed rivers developed on an impermeable substratum; it reaches 1·1 to 1·5 years when the catchment size of these rivers exceeds 250km². Rivers incised in the soft schists of the Famenne show larger channel capacity at bankfull stage, a small width/depth ratio and thus higher recurrence intervals (1·4–5·3 years with T_a and 1–4·4 years with T_p). Baseflow-dominated gravel-bed streams and sandy or silty rivers experience less frequent bankfull discharges, with a recurrence interval higher than 2 or even 3 years (T_p). © 1997 John Wiley & Sons, Ltd.  相似文献   

Climatological Characteristics of the East Asian Winter Monsoon Simulated by CWRF Regional Climate Model     

Bingdi Wang  Qingquan Li  Xinyong Shen  Lili Dong  Fang Wang  Tao Wang  Xinzhong Liang 《地球科学进展》2020,35(3):319-330

Based on the ERA-Interim atmospheric reanalysis data from the European Medium-Term Weather Forecast Center from 1979 to 2016 and the ERSSTv4 sea surface temperature data from the US National Oceanic and Atmospheric Administration, the regional climate model CWRF was used to simulate the climate characteristics in East Asia. The results show that the CWRF model can well reproduce the average characteristics of the East Asian winter monsoon circulation, including the location and intensity of the low-level continental cold high pressure and variation characteristics of wind field in high and low levels. The occurrence area and frequency of the north wind in the simulation and the reanalysis data were further calculated and compared. It is shown that they are basically consistent. The distribution of air temperature and precipitation over China are well represented by the model. The water vapor transport is also in good agreement with the reanalysis data. The water vapor from the Bay of Bengal plays a vital role in the precipitation over South China. The simulation results of apparent heat source and apparent moisture sink show that the model can well simulate the thermal difference between the East Asian continent and the adjacent sea area. The analysis results indicate that CWRF model has the ability to simulate the main characteristics of the East Asian winter monsoon.  相似文献   

太湖生态脆弱性特征与消除对策的初步探讨   总被引：7，自引：2，他引：5  

黄益斌  崔广柏  朱德明 《湖泊科学》1999,11(4):316-321

本文研究了Ｈｇ＾２＋,Ｃｄ＾２＋对痧生经济植物莼菜冬芽茎叶叶绿素含量,叶绿素ａ／ｂ值,可溶性蛋白含量,Ｏ＾－２含量以及活笥氧清除系统活性（ＳＯＤ,ＣＡＴ,ＰＯＤ）的影响,实验结果表明：叶绿素含量,叶绿素ａ／ｂ值、可溶性蛋白含量随着Ｈｇ＾２＋,Ｃｄ＾２＋处理浓度的加大呈下降趋势;  相似文献   

华南冬季准静止锋年际变异特征及其对东亚气候的影响     

徐碧裕  简茂球 《热带气象学报》2023,(4):581-592

基于JRA55再分析资料、观测的降水量和海表温度等数据,利用统计诊断方法分析了华南冬季气候准静止锋的主要变异特征,并探讨了其与环流、海温及东亚气候的联系。华南冬季气候准静止锋的主要变异模态表现为强度变异模态和经向位置变异模态,它们以年际变化为主。类东部型ENSO海温异常及热带中西印度洋海温异常对华南准静止锋强度的年际变异有显著影响;而类中部型ENSO海温异常型显著影响着华南气候准静止锋的南北位置。华南冬季准静止锋的强度变异对东亚副热带地区的降水、以及我国东部内陆地区的近地面气温有显著影响;华南冬季准静止锋南北位置变异则显著影响我国江淮流域降水、以及我国华南至东南沿海一带的近地面气温。华南冬季准静止锋的强度变异模态对东亚的降水和近地面气温的影响范围较位置变异模态都要大。  相似文献   

An improved optical flow method to estimate Arctic sea ice velocity (winter 2014?2016)     

Haili Li  Changqing Ke  Qinghui Zhu  Xiaoyi Shen  Mengmeng Li 《海洋学报(英文版)》2021,40(12):148-160

1 Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology/Key Laboratory for Land Satellite Remote Sensing Applications of Ministry of Natural Resources, School of Geography and Ocean Science, Nanjing University, Nanjing 210023, China; 2 Collaborative Innovation Center of Novel Software Technology and Industrialization, Nanjing 210023, China; 3 Collaborative Innovation Center of South China Sea Studies, Nanjing 210023, China  相似文献   

用NOAA气象卫星AVHRR的定量资料计算冬小麦种植面积的两种方法     

肖乾广 《遥感学报》1989,(3)

本文提出了用NOAA气象卫星AVHRR的定量资料计算冬小麦种植面积的方法,即绿度指数法和单通道法。绿度指数法是根据冬小麦在特定生育期内绿度值基本上保持为常数的特点,用几块巳知样地的种植面积,推算整体种植面积;单通道法是只使用AVHRR第二通道的反照率来计算冬小麦种植面积。这两种方法的优点在于不需考虑大气削弱的订正处理问题,从而使计算得以简化。  相似文献   

冬小麦农田不同高度极端气温预测[ ]          下载免费PDF全文

朱保美  李密  张继波  宰德炜 《沙漠与绿洲气象(新疆气象)》2024,18(4):166-173

利用2019年1月—2022年6月冬小麦农田小气候自动观测站观测的数据和齐河县国家基本气象观测站同期观测资料,采用多元线性回归和BP神经网络方法,建立冬小麦农田30 cm、60 cm、150 cm日最高和日最低气温预测模型。结果表明:两种模型对农田气温的预测效果均较好,阴天条件下150 cm最高气温预测效果最好;晴天条件下30 cm最高气温预测效果最差。两模型模拟结果分层次看,农田气温的模拟精度150 cm>60 cm>30 cm;分天气类型看,多元回归模型农田各层气温的模拟精度阴天>多云>晴天,BP神经网络模型农田30 cm、60 cm最高气温的模拟精度多云>阴天>晴天,农田30 cm最低气温的模拟精度多云与阴天相同,均大于晴天,农田60 cm最低气温的模拟精度晴天>多云>阴天,农田150 cm最高及最低气温的模拟精度晴天与多云相同,均大于阴天;分要素看,30 cm最低气温的模拟精度高于最高气温、60 cm和150 cm最高气温的模拟精度高于最低气温。通过比较,BP神经网络模型的预测精度比多元线性回归模型的预测精度高。两种模型均能满足冬小麦农田气温的预测需求。  相似文献   

East Asia winter monsoon variations on a millennial time‐scale before the last glacial–interglacial cycle     

Huayu Lu  Ko Van Huissteden  Zhisheng An  Govert Nugteren  Jef Vandenberghe 《第四纪科学杂志》1999,14(2):101-110

Grain size and magnetic susceptibility measurements on samples from a typical loess–palaeosol sequence on the central Chinese Loess Plateau are used to reconstruct the Pleistocene East Asian monsoon climate. The coarse‐grained fraction, i.e. the weight percentage > 30 μm of the bulk grain‐size distribution, is used as a sensitive proxy index of the East Asia winter monsoon strength. On the basis of an absolute time‐scale, time‐series variations of this proxy show that winter monsoon strengths varied on millennial time‐scales during the periods 145–165, 240–280, 320–350, 390–440, 600–640, 860–890, 900–930 and 1330–1400 kyr BP. The wavelength of these climatic oscillations varied between 1.89 and 4.0 kyr, as is shown by spectral analysis using the multitaper method. Although numerical simulation experiments show that high frequencies also can arise from measurement errors in the grain‐size analysis, the frequencies prove to be sufficiently stable when the spectral analysis is repeated with a different number of tapers. For the time being, we do not correlate these climatic oscillations with palaeoclimatic records in the North Atlantic deep‐sea sediments because both time‐scales need to be further improved. Our data, however, certainly demonstrate that millennial‐scale East Asian winter monsoon variations in the last 1.4 million years can be detected from terrestrial loess records. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

近50年中国冬季大地冷涡与春夏季干旱相关的统计   总被引：2，自引：1，他引：1  

汤懋苍  张拥军  李栋梁 《气象学报》2005,63(6):1006-1009

通过对冬季大地冷涡与春夏季干旱的相关分析,发现:除高原主体外,冬季的大地冷涡对应着春夏季为干旱少雨区;而且大地冷涡东面的地冷涡绝大多数也是春夏季的干旱少雨区。冬季大地冷涡在中国的出现频率为80%,可作为短期气候预测的重要因子。  相似文献   

冬季大风影响下的渤黄海水交换特征   总被引：1，自引：0，他引：1  

宋军  郭俊如  李静  牟林  刘玉龙  王国松  李琰  李欢 《海洋学报(英文版)》2017,36(1):17-25

利用ROMS海洋数值模式对2006年冬季渤黄海的海洋动力环境进行模拟,基于温度、盐度模拟结果,使用谱混合模型进行水团分析,定义了渤海海峡地区的水交换区。并进一步讨论了冬季大风事件对水交换区的影响,给出了冬季大风影响下的渤黄海水交换特征。研究得出,冬季的黄海水团以“舌”形分布于渤海海峡地区,水交换区则表现为沿“舌”形边缘呈带状分布,具有西北——东南的走向趋势,并且在“舌”尖处的水交换面积最大。通过缩小研究范围,发现位于黄海最北部的沿岸海域并不参与渤黄海之间的水体交换。最后研究发现,冬季大风事件对渤海水交换具有促进作用,具体表现为：大风过程使黄海暖流对渤海的入侵更加深入,水交换区向渤海方向伸展,南部的水交换带变宽,河流径流进入渤海后与渤海水的混合区加大,并发生北移。  相似文献