沪宁高速公路大雾及气象要素特征分析   总被引：3，自引：0，他引：3  

吴和红  严明良  缪启龙  段春锋 《气象与减灾研究》2010,33(4):31-37

利用2006年6月-2009年5月沪宁高速公路AWM自动气象站资料,研究了不同类型大雾持续时间、能见度变化及其出现过程中风、湿度变化特征。结果表明,有超过50%的大雾会发展成浓雾;大雾持续时间以平流雾最长,辐射雾最短;67.6%的大雾在长时间低能见度之前会出现类似"象鼻"形的突变前兆,这可能与地理环境有关;大雾过程中风向以东风和西风为主,锋面雾有部分为偏南风;平流雾发生时风速较辐射雾和锋面雾大,锋面雾发生时风速较多为静风,结束时风速快速增大;平流雾发生时相对湿度多有突变,而辐射雾、锋面雾的相对湿度以渐变为主。  相似文献   

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

A. Retalis  P. Nastos  D. Retalis 《Atmospheric Research》2009,91(2-4):219-228

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.  相似文献   

Modeling coupled THM processes of geological porous media with multiphase flow: Theory and validation against laboratory and field scale experiments   总被引：3，自引：0，他引：3  

Yifeng Chen  Chuangbing Zhou  Lanru Jing   《Computers and Geotechnics》2009,36(8):1308-1329

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.  相似文献   

末次冰期冰盛期中国地区水循环因子变化的模拟研究   总被引：2，自引：1，他引：1  

刘煜  李维亮  何金海  陈隆勋 《气象学报》2008,66(6):1005-1019

ISCCP卫星资料(1983—2006年)的结果显示:青藏高原地区是高云的高值中心;而以四川为中心直到同纬度的中国东南沿海地区是中云的高值区,同时,青藏高原地区是中云的低值中心。利用全球气候模式CCM3嵌套区域模式MM5模拟了现代和末次冰期冰盛期的气候。MM5模拟的结果与ISCCP的卫星资料对比表明:模拟结果再现了中国地区高云和中云分布的主要特征。这暗示云分布的气候特征可能主要由相对湿度决定。同时,通过MM5的结果与NCEP资料的对比也说明,模式可以较好地模拟水汽和温度的垂直分布。在此基础上,研究了末次冰期冰盛期水循环因子的变化。模拟结果显示:末次冰期冰盛期夏季对流层的温度降低,在对流层中上层存在温度降低的中心;而在冬季在南方的对流层中层存在降温中心,在北方的对流层中上层温度升高。大气中水汽含量与温度变化有很好的正相关,除了冬季北方对流层中上层水汽增加外,水汽含量一般降低,而且在近地层降低的最多,随高度增高水汽变化逐渐变小。但是,水汽的相对变化在对流层上层存在降低的高值中心。相对湿度存在变化,最大的变化超过15%,而且有增加,也有减少。在区域尺度相对湿度不是保守的。相对湿度变化与中云和低云的变化一致。在末次冰期冰盛期,中国地区高云量减少,除中国西南地区外,中云和低云量减少,低云量减少的最多。降水的变化与中云和低云的变化相对应,云量增加降水增加,云量减少降水也减少。从相对湿度和有效降水可以看到在西南地区末次冰期冰盛期变得潮湿,在夏季西北地区也变得潮湿。  相似文献   

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

Goberville E  Beaugrand G  Sautour B  Tréguer P 《Marine pollution bulletin》2011,62(8):1751-1761

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.  相似文献   

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

Denis Wirrmann  Anne-Marie Sémah  Jean-Pierre Debenay  Magali Chacornac-Rault 《Quaternary Research》2011,76(2):229-242

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.  相似文献   

黄山地区气溶胶吸湿增长特性数值模拟研究   总被引：4，自引：2，他引：2  

江琪  银燕  秦彦硕  陈魁  杨素英 《气象科学》2013,33(3):237-245

应用多种化学组分气溶胶的绝热气块分档模式,对2008年春季黄山地区气溶胶吸湿增长特性进行了模拟分析.结果表明:黄山地区气溶胶吸湿增长因子f的大小与粒子半径、相对湿度、粒子化学组分、上升速度及上升高度密切相关,且小粒子吸湿增长比大粒子显著.吸湿增长因子与相对湿度呈正相关,相对湿度越接近粒子的临界饱和比,吸湿增长因子变化越显著.可溶性有机气溶胶,通过增加溶液中溶质的百分比来影响临界饱和比,使吸湿增长因子增大.若不考虑不可溶粒子的成核作用,会高估粒子的吸湿性.随着上升速度增大,吸湿增长因子降低,降低程度与粒子初始高度的相对湿度有关.上升高度通过改变气块相对湿度的变化来影响气溶胶吸湿增长因子.  相似文献   

江西省盛夏极端高温的气候变化及短期气候预测   总被引：2，自引：0，他引：2  

朱珍  章开美  陈胜东  杨华 《气象与减灾研究》2013,(3):12-17

利用江西省82个代表站1961-2009年逐日最高温度资料和NECP/NCAR的逐月平均500 hPa高度场资料,分析了江西省极端高温天气的气候变化特征,以及盛夏酷暑年、凉夏年同期及前期环流的差异。结果表明：（1）江西省极端高温天气是与旱季相联系的,极端高温天气主要集中在盛夏（7-8月）,占夏半年的79.7％,以赣北的南部更明显;而4-6月只占10.2％,且4-6月赣北的南部为极端高温天气发生概率的极小值区。（2）20世纪90年代末期至21世纪初,江西省极端高温天气呈增加趋势,并且21世纪以后为极端高温天气偏多期。（3）酷暑年盛夏500 hPa位势高度距平场上,在蒙古、西伯利亚有着广阔的负距平区,蒙古高压减弱,阻塞高压不易形成,冷空气不容易在高纬度地区堆积,同时西太平洋副热带高压异常偏强,阻挡冷空气,使其不能继续南下影响江西省,易造成高温天气。（4）初夏（6月）500 hPa位势高度距平场上,东亚大槽位置上有弱正距平,鄂霍次克海以北的俄罗斯及中高纬大陆地区都为负距平区,阿留申群岛附近为正距平区,对应盛夏期东亚大槽位置上正距平加强,中高纬的负距平中心增强,并北抬至40＆#176;N以北,整个江南地区上空受正距平中心控制,副高加强,易造成江西省盛夏极端高温天气偏多。  相似文献   

用图解法表示控制相对海平面变化因素及其对沉积地层分布模式的影响     

张国仁 《国土资源》1997,(2)

本文从层序地层学中有关术语（如全球海平面变化、地壳沉降、相对海平面变化、可容纳空间、水深、沉积物保留区、剥蚀区及沉积分布模式等）的概念和基本原理入手，通过列举实例，采用定量方法和作出相应的图件来表示控制相对海平面变化的因素、有关参数间相互关系以及对沉积地层分布模式的影响，旨在进一步加深对层序地层学理论和方法的认识及理解，从而提高区域地层研究程度。  相似文献   

Modelling natural formations of LEO satellites     

M. Halsall  P. L. Palmer 《Celestial Mechanics and Dynamical Astronomy》2007,99(2):105-127

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