Estimation of the Exchange Coefficient of Heat During Low Wind Convective Conditions     

Kusuma G. Rao 《Boundary-Layer Meteorology》2004,111(2):247-273

For the first time, the exchange coefficient of heat C_H has been estimated from eddy correlation of velocity and virtual temperature fluctuations using sonic anemometer measurements made at low wind speeds over the monsoon land atJodhpur (26°18' N, 73°04' E), a semi arid station. It shows strong dependence on wind speed, increasing rapidly with decreasing wind speed, and scales according to a power law C_H = 0.025U₁₀ ^-0.7 (where U₁₀ is the mean wind speed at 10-m height). A similar but more rapid increase in the drag coefficient C_Dhas already been reported in an earlier study. Low winds (<4 m s^-1) are associated with both near neutral and strong unstable situations. It is noted that C_H increases with increasing instability. The present observations best describe a low wind convective regime as revealed in the scaling behaviour of drag, sensible heat flux and the non-dimensional temperature gradient. Neutral drag and heat cofficients,corrected using Monin–Obukhov (M–O) theory, show a more uniform behaviour at low wind speeds in convective conditions, when compared with the observed coefficients discussed in a coming paper.At low wind convective conditions, M-O theory is unable to capture the observed linear dependence of drag on wind speed, unlike during forced convections. The non-dimensional shear inferred from the present data shows noticeable deviations from Businger's formulation, a forced convection similarity. Heat flux is insensitive to drag associated with weak winds superposed on true free convection. With heat flux as the primary variable, definition of new velocity scales leads to a new drag parameterization scheme at low wind speeds during convective conditionsdiscussed in a coming paper.  相似文献   

一次右移传播的强对流风暴研究          下载免费PDF全文

范皓  吴正华段英 《应用气象学报》2004,15(4):445-455

对1998年6月21日华北平原强对流风暴的天气动力学分析表明, 这次强对流风暴是发生在华北区域出现前倾性阶梯槽形势下, 对流层中、下层的差动温度平流和干暖盖的存在是对流不稳定层结形成和发展以及有效对流能量存储的重要条件;对流层中、低层的西风扰动触发对流云团生成, 而对流云团在明显右移传播过程中不断发展增强, 是与对流云团南侧存在明显的动压垂直加速度、高能暖湿气流的不断输入以及对流云团的合并有关。  相似文献   

“99.6”梅雨锋暴雨对流动量输送特征的诊断分析   总被引：4，自引：0，他引：4  

隆霄  程麟生 《气象学报》2004,62(4):439-448

利用MM 5V3输出的高时空分辨率资料对“99.6”梅雨锋暴雨过程中对流动量输送特征X进行了诊断分析研究 ,主要结论如下 :( 1)模拟结果和观测分析的比较表明 ,中尺度模式MM 5V3能够成功地模拟“99.6”梅雨锋暴雨中尺度系统的发生和发展及演变。 ( 2 )通过对中尺度系统强烈发展时刻的对流动量输送 (CMT)诊断分析表明 :动量收支残差与平均流场的方向一致 ,它有利于加速西南气流北上 ,和 β中尺度系统的发生和发展 ;结果也表明强矢量几乎总是与产生强烈上升运动的 β中尺度系统相对应。动能转换的诊断表明 ,低涡前部的相间出现E >0和E<0的区域 ,这显示出在中尺度系统强烈发展时大尺度系统与中尺度系统之间的能量转换非常复杂 ,并不是简单的能量串级过程所能描述的 ;同时E的正值比负值的绝对值要大得多 ,这表明能量主要是从大尺度向次网格尺度转换 ,激发次网格尺度系统的发生和发展。 ( 3 )当切变线低涡离陆入海时 ,X矢量则对西南气流产生强烈的减速作用。 v和 vY的垂直剖面分析显示 ,南风此时在对流层中低层受到明显的减速作用。 ( 4 )转换能量E的垂直廓线显示 ,在中尺度系统强烈发展时 ,对流层中低层的能量顺尺度 (E >0 )输送非常强 ,而在低涡切变线离陆入海时 ,对流层则表现为逆尺度输送 (E <0 )。  相似文献   

地下水动态多年周期与中强震多发期   总被引：6，自引：6，他引：6  

张素欣  温学勤  郑云贞  张子广 《华北地震科学》2002,20(1):32-37

地下水动态的短期变化特征已有很深入的研究,本文根据唐山地区6口井1982年－2001年9月的水位动态变化月均值资料探讨地下水的长期变化特征。初步研究表明，从多年较大空间的地下水动态变化看，可视为较平衡的随机过程，存在着10年左右的周期结构，这种周期结构与地质构造环境、水文地质环境、地理地貌、观测层位、补给和排泄条件以及观测井结构关系不密切，这种现象可能与复杂的全息天体运动有关，是一种多种周期的叠加，是一种合力作用，代表着区域应力场。  相似文献   

The preliminary heat flow map of Europe and some of its tectonic and geophysical implications     

Vladimír Čermák  Eckart Hurtig 《Pure and Applied Geophysics》1978,117(1-2):92-103

The heat flow map of Europe was derived from 2605 existing observations, which for this purpose were supplemented by numerous results of deep borehole temperatures, gradients and local heat flow patterns. In areas without data the heat flow field was extrapolated on the basis of the regional tectonic structure and the observed correlation of heat flow and the age of the last tectono-thermal event. The heat flow pattern as obtained in the map may be described by two components: (i) regional part and (ii) local part of the measured surface geothermal activity. The regional part of the heat flow field in Europe is dominated on the whole by a general north-east to south-west increase of the geothermal activity, which is an obvious consequence of the tectonic evolution, the major heat flow provinces corresponding thus to the principal tectonic units. The geothermal fine structure (local part) superimposing the former is mainly controlled by local tectonics, especially by the distribution of the deep reaching fracture zones and by the hydrogeological parameters. The correlation between the heat flow pattern and the crustal structure allows some preliminary geophysical implications: (a) areas of the increased seismicity may be connected with the zones of high horizontal temperature gradient, (b) increased surface heat flow may be generally observed in the zones of weakened crustal thickness, (c) there are considerable regional variations in the calculated temperature on the Moho-discontinuity, as well as in the upper mantle heat flow contribution.  相似文献   

Flow visualization studies of two-phase thermal convection in a porous layer     

C. H. Sondergeld  D. L. Turcotte 《Pure and Applied Geophysics》1978,117(1-2):321-330

Summary Two-phase thermal convection has been studied in a porous layer heated from below. A water saturated porous layer was heated so that boiling occurred on the lower boundary. In order to observe flow patterns one lateral dimension of the apparatus was made small. At moderate heat fluxes a water zone overlay a two-phase, steam-water zone. Water velocities and streamlines were obtained as well as the location of the two-phase zone for several heat fluxes. Within the water zone heat transfer took place due to both conduction and convection. In the two-phase zone heat transfer took place due to counterpercolation of steam and water.  相似文献   

A simple theory for the vertical structure of the tropical atmosphere     

E. S. Sarachik 《Pure and Applied Geophysics》1985,123(2):261-271

It is suggested that the gross mean vertical structure of the undisturbed tropical atmosphere may be understood in terms of convective boundary layers driven in different ways and on different time scales by the evaporation of water from the sea surface. The mixed layer on a short time scale is driven partly by the buoyancy produced by the light weight of the water vapor; the trade cumulus layer on an intermediate time scale by the buoyancy (but not heating) produced by the condensation of the water vapor in shallow trade cumulus clouds; and the troposphere itself on a long time scale by the buoyancyand heating produced by the condensation of the water vapor in the deep cumulonimbus clouds.May 1985This paper was issued as a Harvard University report in 1974. For this version only Section 5 has been rewritten. There has been sufficient interest in this work over the years to warrant making it more widely available through the open literature.Contribution No. 783 from NOAA/Pacific Marine Environmental Laboratory  相似文献   

Nile floods recorded in deep Mediterranean sediments     

Emmanuelle Ducassou  Thierry Mulder  Sbastien Migeon  Eliane Gonthier  Anne Murat  Marie Revel  Lucilla Capotondi  Stefano M. Bernasconi  Jean Mascle  Sbastien Zaragosi 《Quaternary Research》2008,70(3):382-391

Clastic mud beds rich in continental organic matter are observed recurrently in the Nile deep-sea turbidite system. They formed during flooding periods of the river similar to those that induce sapropel formation and occurred during periods of increased density stratification of the eastern Mediterranean. The very fine-grained flood deposits are intercalated within pelagic sediments, sapropels and Bouma-type turbidites. These flood deposits form by the successive reconcentrations of surface (hypopycnal) plumes by convective sedimentation, which in turn generate a fine-grained low-energy hyperpycnal flow. Sea-level high stands seem also to favor hypopycnal plume formation and increase clastic mud bed formation. Consequently, these muddy clastic beds provide a direct link between deep-marine sedimentary records and continental climatic change through flood frequency and magnitude.  相似文献   

Post-collisional Plio-Pleistocene shoshonitic volcanism in the western Kunlun Mountains, NW China: Geochemical constraints on mantle source characteristics and petrogenesis   总被引：4，自引：0，他引：4  

Zhaochong Zhang  Xuchang Xiao  Jun Wang  Yong Wang  Timothy M. Kusky 《Journal of Asian Earth Sciences》2008,31(4-6):379-403

Major and trace element, Sr–Nd–Pb isotope and mineral chemical data are presented for post-collisional late Cenozoic shoshonitic volcanic rocks from the western Kunlun Mountains, NW China. They are distributed in two approximately E–W striking sub-belts, with the lavas in the southern sub-belt having been generated earlier than those in the northern sub-belt. The mineralogy of the rocks reflects crystallization from moderate temperature magmas (700–1000 °C) with high oxygen and water fugacities. They are geochemically characterized by relatively low TiO₂, Al₂O₃ and FeO and high alkalies coupled with very high contents of incompatible element concentrations. Remarkably negative Nb, Ta and Ti anomalies are displayed on primitive mantle-normalized incompatible element patterns. In addition, they show a relatively broad range of low ε_Nd (−1.8 to −8.7) at more restricted ⁸⁷Sr/⁸⁶Sr ratios (0.7081–0.7090). Pb isotopes are characterized by a range of ²⁰⁷Pb/²⁰⁴Pb (15.48–15.74) and ²⁰⁸Pb/²⁰⁴Pb (38.30–39.12) ratios at relatively invariant ²⁰⁶Pb/²⁰⁴Pb (18.60–18.83) values, except one sample with a ratio of 18.262, leading to near-vertical arrays. The lavas from the northern sub-belt have relatively high ⁸⁷Sr/⁸⁶Sr ratios. All lavas have extremely high La/Yb ratios, probably reflecting that the magmas were derived from a metasomatized lithospheric mantle source containing phlogopite–hornblende garnet peridotite affected by subducted sediments and hydrous fluids, rather than from a depleted asthenopheric mantle source or mantle plume source. However, the lavas from the southern sub-belt were derived from a lower degree of melting of more highly metasomatized sub-lithospheric mantle in comparison with those from the northern sub-belt. Processes responsible for partial melting of metasomatized lithospheric mantle and post-collision magmatism in the western Kunlun could be a consequence of continuously conductive heating of upwelling, hot asthenospheric mantle following the delamination subsequent to thickening, which is consistent with the spatial and temporal geochemical variations in shoshonitic rocks in Tibet.  相似文献   

区域地震信号自动识别方法及应用(英文)   总被引：2，自引：0，他引：2  

刘希强  蔡寅  赵瑞  曲保安  赵银刚  冯志军  李红 《应用地球物理》2014,11(2):128-138

地震信号的实时、自动、准确识别对于地震自动速报和地震预警十分重要。仿真信号试验分析表明,观测数据的四阶统计量函数(BKCF)对信号与噪声在能量和(或)频率方面的微弱差异变化具有较高的分辨能力。以此为基础,本文提出了一种新的自动探测区域地震事件的方法和测定直达波震相到时的BKCF-AIC方法。为了进一步提高波震相到时测定的精度,本文首先对指定时段的P-波记录进行偏振特性分析,其次对含有P波的S波记录进行偏振滤波处理,再次应用上述方法测定震相到时。与传统算法相比,基于山东测震台网记录的区域地震震例分析结果表明,使用本文提出的方法能够大幅度降低地震事件误检、漏检率,进一步提高了震相识别精度。  相似文献