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101.
Temporal variations of reference evapotranspiration and controlling factors: Implications for climatic drought in karst areas
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Guo Xiao-jiao Wang Wen-zhong Li Cheng-xi Wang Wei Shi Jian-sheng Miao Ying Hao Xing-bo Yuan Dao-xian 《地下水科学与工程》2022,10(3):267-284
Variations in reference evapotranspiration (ET0) and drought characteristics play a key role in the effect of climate change on water cycle and associated ecohydrological patterns. The accurate estimation of ET0 is still a challenge due to the lack of meteorological data and the heterogeneity of hydrological system. Although there is an increasing trend in extreme drought events with global climate change, the relationship between ET0 and aridity index in karst areas has been poorly studied. In this study, we used the Penman–Monteith method based on a long time series of meteorological data from 1951 to 2015 to calculate ET0 in a typical karst area, Guilin, Southwest China. The temporal variations in climate variables, ET0 and aridity index (AI) were analyzed with the Mann–Kendall trend test and linear regression to determine the climatic characteristics, associated controlling factors of ET0 variations, and further to estimate the relationship between ET0 and AI. We found that the mean, maximum and minimum temperatures had increased significantly during the 65-year study period, while sunshine duration, wind speed and relative humidity exhibited significant decreasing trends. The annual ET0 showed a significant decreasing trend at the rate of ?8.02 mm/10a. However, significant increase in air temperature should have contributed to the enhancement of ET0, indicating an “evaporation paradox”. In comparison, AI showed a slightly declining trend of ?0.0005/a during 1951–2015. The change in sunshine duration was the major factor causing the decrease in ET0, followed by wind speed. AI had a higher correlation with precipitation amount, indicating that the variations of AI was more dependent on precipitation, but not substantially dependent on the ET0. Although AI was not directly related to ET0, ET0 had a major contribution to seasonal AI changes. The seasonal variations of ET0 played a critical role in dryness/wetness changes to regulate water and energy supply, which can lead to seasonal droughts or water shortages in karst areas. Overall, these findings provide an important reference for the management of agricultural production and water resources, and have an important implication for drought in karst regions of China. 相似文献
102.
《New Astronomy》2015
The inertial and gravitational mass of electromagnetic radiation (i.e., a photon distribution) in a cavity with reflecting walls has been treated by many authors for over a century. After many contending discussions, a consensus has emerged that the mass of such a photon distribution is equal to its total energy divided by the square of the speed of light. Nevertheless, questions remain unsettled on the interaction of the photons with the walls of the box. In order to understand some of the details of this interaction, a simple case of a single photon with an energy bouncing up and down in a static cavity with perfectly reflecting walls in a constant gravitational field , constant in space and time, is studied and its contribution to the weight of the box is determined as a temporal average. 相似文献
103.
GRAPES_GFS中三维参考大气的研究:参考态构造和实际预报试验 总被引:1,自引:0,他引:1
GRAPES_GFS(Global Regional Assimilation and PrEdiction System, Global Forecast System)采用基于等温大气构造的一维参考大气,前期的研究工作已在GRAPES_GFS的动力框架中引入了三维参考大气,并通过一系列理想试验检验了新方法的正确性以及计算精度。本部分研究工作,主要针对实际资料的预报试验,对比分析了不同三维参考态给定方法的优劣,并采用气候平均法,进行夏季两个月的四维变分循环预报试验。检验结果显示,使用三维参考大气后,模式的综合预报性能得到了提升,对流层高度场、温度场的预报偏差有所减小,长期积分过程中模式质量损失较为严重的问题也得到了明显的缓解。另外,通过动能谱的对比也可以看到使用三维参考大气后,模式在高层的能量耗散明显较小,能谱变化与观测更加吻合。 相似文献
104.
1997年11月14日晚,在中国科学院云南天文台1米望远镜上用新安装的10242CCD观测到了木星的两颗伽里略卫星;Europa和Callisto及一颗依巴谷星(星号为 104297).当采用新的 JPL DE405和 Sampson-Lieske理论(G5)计算卫星的理论位置并相对于Callisto测量恒星位置时,视位置的观测值与计算值之差的平均值在赤经和赤纬方向分别为△α=-0″029±0.″012,△δ=0.″005± 0.″011.这对应于平均观测历元(UT):1997年11月14日13时43分50秒.这一试验结果与 Casas等在同一时期内CCD观测的结果有着很好的一致性 它反映了依巴谷星表体现的光学参考系与DE405体现的动力学参考系在观测历元具有较好的一致性.单次位置测定的标准误差在赤经赤纬方向分别为±0.″052和0.″047.这一精度明显优于 Casas等人发表的 Callisto的处理精度,并与目前国际上最好的伽里略卫星观测精度相当 相似文献
105.
本文用多维谱分析的方法研究了1985年1月-1987年12月南极长城站地面气象要素的谱特征。该地区的气象要素与北半球一样,也普遍存在3-5天、准一周、准二周和3-4周振荡周期。在长城站所在的乔治王岛地区,从地面到平流层中下部,气压系统都存在着显著的准二周振荡,这种振荡是由上往下传播的。无论冬、夏季,准二周和准一周振荡都是由西往东传播的,而扰动的南北传播方向则与季节及振荡周期长度有关。南极地区的中期振荡特征与500hPa极地涡旋的活动和强度变化有密切关系。 相似文献
106.
本文扼要介绍了中国科学院东川泥石流观测研究站对外开放三年来,在泥石流观测试验研究和防灾减灾工作中的新进展,同时也简述了站设基金课题、国家基金课题和中外合作交流项目的进展情况,并对今后的观测研究工作提出了展望和建议。 相似文献
107.
全面分析了全球地面天气报数据集区站号存在的问题、错误区站号的存在对使用资料的影响以及错误区站号产生的原因,提出了解决错误区站号的相应处理方法.同时,对处理后的全球地面天气报数据集区站号的情况和原数据集区站号进行比较分析. 相似文献
108.
A new and comprehensive method is presented that can be used for estimating eccentricity vectors between global positioning system (GPS) antennas, doppler orbitography and radiopositioning integrated by satellites (DORIS) antennas, azimuth-elevation (AZ-EL) very long baseline interferometry (VLBI) telescopes, and satellite laser ranging (SLR) and lunar laser ranging (LLR) telescopes. The problem of reference point (RP) definition for these space-geodetic instruments is addressed and computed using terrestrial triangulation and electronic distance measurement (EDM) trilateration. The practical ground operations, the surveying approach and the terrestrial data processing are briefly illustrated, and the post-processing procedure is discussed. It is a geometrically based analytical approach that allows computation of RPs along with a rigorous statistical treatment of measurements. The tight connection between the geometrical model and the surveying procedure is emphasized. The computation of the eccentricity vector and the associated variance–covariance matrix between an AZ-EL VLBI telescope (with or without intersecting axes) and a GPS choke ring antenna is concentrated upon, since these are fundamental for computing the International Terrestrial Reference Frame (ITRF). An extension to RP computation and eccentricity vectors involving DORIS, SLR and LLR techniques is also presented. Numerical examples of the quality that can be reached using the authors approach are given. Working data sets were acquired in the years 2001 and 2002 at the radioastronomical observatory of Medicina (Italy), and have been used to estimate two VLBI-GPS eccentricity vectors and the corresponding SINEX files. 相似文献
109.
重点介绍了高精度确定大型天线几何旋转中心的观测方案和计算方法。结合具体实例,在ITRF2000框架下,论述了控制网布设、观测方案确定、数学模型的建立、数据处理的过程,结果与已知外部参考结果进行了比较,坐标分量上达到毫米级外附精度,验证了观测、计算方案的可行性和准确性。 相似文献
110.