有限水分胁迫对小麦生长状况的影响及合理灌溉的土壤相对湿度指标

在人工控制水分条件下 ,通过田间小间隔不同水分等级和持续时间试验 ,分析了水分胁迫对小麦生理、生态及产量的影响 ,探讨了小麦对不同水分胁迫后复水的滞后作用和补偿效应 ,得出了有利于小麦高产、高效的轻度水分胁迫临界土壤相对湿度指标为 55% .     

大气气溶胶散射吸湿增长特性研究进展

大气气溶胶的散射吸湿增长特性反映了相对湿度对气溶胶散射能力的影响。研究气溶胶散射吸湿增长对于评估气溶胶辐射强迫、了解气溶胶对大气能见度的影响具有重要意义。文中对气溶胶散射吸湿增长特性的研究意义、监测方法、中外研究进展、参数化拟合和模型模拟等方面进行了系统回顾和总结,并对未来发展方向做出展望。中国在该领域开展的研究数量偏少,广泛开展气溶胶散射吸湿增长特性研究十分必要。     

中国降水异常的特征分析

异常降水直接影响着农业和其他生产活动。文中计算分析了中国160个测站的一些反映降水变化的常规统计量,认为这些统计量难以反映出降水异常的变化特征。文中从非线性动力学和统计学相结合的角度出发,分析了相隔1～20 a间不同时间尺度的降水变率之间的关系,找到可以区分任意地区降水异常特点的特征参数,由此可进一步判断某个地区旱涝灾害发生的可能性以及强度的大小,为气候研究工作提供必要的依据。     

模拟多年冻土活动层厚度对气候变化的响应

在气候变化背景下,活动层厚度的变化会对多年冻土区水文,生态,寒区工程等产生较大的影响.本研究利用中科院气候系统模式CAS-FGOALS-g3和陆面过程模式CAS-LSM模拟分析了活动层厚度的变化趋势和相对变化.结果表明:活动层厚度整体上呈现出增加的趋势.1979-2014年,多年冻土区活动层厚度的区域平均为1.08 m...     

太阳活动对京津冀地区旱涝的影响

利用中国气象科学院等整理的中国近五百年旱涝等级资料, 应用小波分析、 相关矩分析等方法, 详细分析了太阳黑子变化与京津冀地区旱涝的关系。在统计太阳黑子极值年附近旱涝特征时发现, 在太阳黑子峰值年附近京津冀地区容易出现偏旱的年份, 低谷年附近容易出现偏涝的年份。小波分析结果表明, 太阳黑子与旱涝指数在9.8年、 78.6年、 132.2年周期处存在对应关系, 说明太阳黑子的变化对京津冀地区的旱涝有一定影响。通过旱涝指数与太阳黑子相对数的相关矩分析, 发现两者相关关系存在阶段性的转折变化, 即由正相关转为负相关, 或者由负相关转为正相关, 相关矩发生转折的时间间隔最长为81年, 最短为23年, 平均为50年。本文还对相关矩阶段性变化的可能原因进行了初步分析。     

参考作物蒸散模型对比分析及评价

利用山东省6个气象台站45 a(1960-2004年)的逐日气象资料并选用7种参考作物蒸散模型,分别计算了上述各地的参考作物蒸散,对模型结果进行时空分布对比分析;进而以FAO推荐的Penman-Monteith模型为对照,利用最小一乘法对其余6种模型进行优化并对优化前后的模型进行时空比较.结果表明:Makkink模型在6个台站的时空分布模拟效果均最好,Mass-transfer模型在7-8月明显偏低,Net Radiation模型各站全年基本都偏高;根据不同月份的相对偏差情况,采用最小一乘法进行分月优化,优化后的模型预测月参考作物蒸散标准误差小于5 mm,平均相对误差小于8.5%,台站的年参考作物蒸散相对误差也基本小于10%,说明这些含参数较少的模型经优化后基本上可用,当资料缺损时不失为Penman-Monteith模型的替代模型.     

Study of small ions concentration in the air above Athens, Greece

Measurements of positive and negative small atmospheric ion concentrations have been made regularly since 1968 at the National Observatory of Athens (NOA). In this paper the 17-year period 1968–1984 is summarized. The diurnal and annual variations are examined, and Fourier analysis is also used for the study of the diurnal variation. The concentrations of small ions follow a double diurnal course. The maxima occur near 3–5 h and 13–16 h local time (LT = GMT + 2 h). The minima are observed at 6–8 h and 21–23 h. The annual course of small ions presents maximum concentration values around the summer season. The mean of the small ion concentration (SIC) for the 17-year period (1968–1984) is n₊ = 188.8 ions/cm³ for positive ions and n₋ = 151.1 ions/cm³ for negative ions. Their ratio is equal to 1.25. The year-to-year variation of SIC for the examined period shows a negative trend. The results from multiple regression analysis show that wind speed and SIC are positively correlated, while relative humidity, smoke and sulphur dioxide are negatively correlated.     

Modeling coupled THM processes of geological porous media with multiphase flow: Theory and validation against laboratory and field scale experiments

A FEM model for analysis of fully coupled multiphase flow, thermal transport and stress/deformation in geological porous media was developed based on the momentum, mass and energy conservation laws of the continuum mechanics and the averaging approach of the mixture theory over a three phase (solid–liquid–gas) system. Six processes (i.e. stress–strain, water flow, gas flow, vapor flow, heat transport and porosity evolution processes) and their coupling effects are considered, which not only makes the problem well-defined, but renders the governing PDEs closed, complete, compact and compatible. Displacements, pore water pressure, pore gas pressure, pore vapor pressure, temperature and porosity are selected as basic unknowns. The physical phenomena such as phase transition, gas solubility in liquid, thermo-osmosis, moisture transfer and moisture swelling are modeled. As a result, the relative humidity and other related variables in porous media can be evaluated on a sounder physical basis. A three dimensional computer code, THYME3D, was developed, with eight degrees of freedom at each node. The laboratory CEA Mock-up test and the field scale FEBEX benchmark test on bentonite performance assessment for underground nuclear waste repositories were used to validate the numerical model and the software. The coupled THM behaviors of the bentonite barriers were satisfactorily simulated, and the effects and impacts of the governing equations, constitutive relations and property parameters on the coupled THM processes were understood in terms of more straightforward interpretation of physical processes at microscopic scale of the porous media. The work developed enables further in-depth research on fully coupled THM or THMC processes in porous media.     

Early evaluation of coastal nutrient over-enrichment: new procedures and indicators

Recent studies have provided compelling evidence for an accelerated anthropogenic impact on coastal systems, resulting in intense inputs of materials and nutrients from the continent. This has led scientists and policymakers to encourage the implementation of monitoring programmes, which have resulted in the multiplicity of datasets. However surprisingly, only a few attempts have been made to couple observations with statistical and mathematical tools to detect, as soon as the data become available perturbations in coastal systems. Here, we propose new mathematical procedures to evaluate the state of a system, based on the building of relative reference state and indicators of nutrient over-enrichment. The techniques were tested in some French coastal systems using data from the programme SOMLIT. Applied to this dataset, the multivariate procedures rapidly identified and evaluated anthropogenic nutrient anomalies from the continent on three sites (Wimereux, Roscoff and Villefranche-sur-Mer) from 1997 onwards.     

Mid- to late Holocene environmental and climatic changes in New Caledonia, southwest tropical Pacific, inferred from the littoral plain Gouaro-Déva

Multiproxy analysis of three littoral cores from western New Caledonia supports the hypothesis that the main controlling factors of environmental changes are sea-level change, ENSO variability and extra-tropical phenomena, such as the Medieval Warm Period (MWP) marked by a tendency for La Niña-like conditions in the tropical Pacific. The record starts during the late Holocene sea-level rise when the terrestrial vegetation indicated wet and cool conditions. The site was a coastal bay definitely transformed into a freshwater swamp at around 3400 cal yr BP, after the rapid drawdown of sea level to its current level. Sediments and foraminiferal assemblages indicated subsequent episodes of freshwater infillings, emersion or very high-energy conditions, likely related to climatic changes and mostly controlled by ENSO variability. Between 2750 and 2000 cal yr BP, relatively dry and cool climate prevailed, while wetter conditions predominated between ca. 1800 and 900 cal yr BP. The Rhizophoraceae peak between ca. 1080 and 750 cal yr BP, coeval with the MWP, may indicate a global phenomenon. Microcharcoal particles present throughout the record increased after 1500 cal yr BP, suggesting an anthropogenic source. From ca. 750 cal yr BP the appearance of current type of vegetation marks the human impact.