一次过冷层状云催化云迹微物理特征的卫星遥感分析

利用卫星反演技术,通过卫星观测到的一次人工增雨催化作业后形成的云迹线个例,分析了云迹线与其周围云的光谱特征、亮温、亮温差、云顶粒子有效半径等云微物理特征,比较了它们之间的差异,揭示了这次过冷层状云催化的微物理效应。云迹实际上是持续时间超过80 min、宽和深分别约为14 km和1.5 km的云谷。云迹周围的云顶粒子有效半径为10—15μm,而云沟内的粒子在15—24μm变化。周围云体由过冷滴组成,中间可能夹杂了一些低浓度的冰粒子,云沟内云的主要成分是冰。和周围未被催化的云相比,0.6μm通道的光谱反射率,在云沟处有明显的增加,而3.7μm通道反射率在云沟内是降低的,尽管其绝对变化幅度不大,但其相对变化幅度较大。随着播云时间的增加,云沟深度、宽度逐渐增加,云沟内和周围云体的温差逐渐增加,对通道4和5而言,在最早催化部位,最大分别达到4.2℃和3.9℃,4和5通道之间云沟内的亮温差也是随冰晶化时间的增加而增加,最大为1.4℃,而云沟周围云为0.2—0.4℃。云沟的形成、云沟内云顶温度的增加和4,5通道之间亮温差的增加,都足以说明被播云体变薄,其原因是由于云顶降水使得云内的水流失,云顶下降。云顶冰晶化、冰粒子增长成降水造成云顶下沉,是云沟形成的主要原因。对于本次播云作业,晶化作用在播云22 min后逐渐显现。在播云后38—63 min,有新的水云在云沟的中间部位生成,可能是由于冻结潜热释放引起的上升运动所致。而新生水云在形成较早的云迹中没有出现,这些较早形成的云迹在80多分钟的整个观测期间持续扩散。最终,在周围云从外向云沟内的扩散过程中,云沟开始消散。     

亚洲中东部岩石圈塑性流动网络与构造应力场

:板块边缘驱动作用主要通过岩石圈下层的网络状塑性流动实现其向板内的远程传递 ,并控制上层的构造变形。相应地造成构造应力场的的多层分布格局 ,主要包括下层 (含下地壳和岩石圈地幔 )、多震层 (属于上部地壳 )和浅层 (浅表地壳 )应力场。这些层中最大压应力方向可分别采用塑性流动网络共轭角平分线、震源机制解和井孔应力测量等方法加以确定。根据对亚洲中—东部下层与多震层应力场的对比表明 ,大部分地区二者的应力方向基本一致 ,表明了下层对上层的控制 ,这对了解板内应力场的一般趋势与格架提供了基础。靠近驱动边界的局部地段 ,由于上部地壳直接的传递作用 ,往往导致上、下层应力方向的显著偏差 ,有可能成为进一步了解深浅层联系和差异的一种方法     

Spatial behaviour of Rayleigh waves in layered half‐spaces under active surface sources

In the free state, Rayleigh waves are assumed to travel in the form of planar wavefronts. Under such an assumption, the propagation behaviour of the modes of Rayleigh waves in layered half‐spaces is only frequency dependent. The frequency behaviour, which is often termed as dispersion, is determined by the shear wave velocity profile of layered soils within the depth related to wavelength (or frequency). According to this characteristic, the shear wave velocity profile can be back‐analysed from the dispersion. The technique is widely used in the surface wave testing. However, the wavefronts of Rayleigh waves activated by the surface sources are non‐planar. The geometric discrepancy could result in Rayleigh waves manifesting distance‐dependent behaviour, which is referred to as spatial behaviour in this paper. Conventional analysis ignoring this spatial behaviour could introduce unexpected errors. In order to take the effects of sources on the propagation behaviour into account, a new mathematical model is established for Rayleigh waves in layered elastic media under vertical disc‐like surface sources using the thin‐layer method. The spatial behaviour of the activated modes and the apparent phase velocity, which is the propagation velocity of Rayleigh waves superposed by the multiple modes, are then analysed. Aspects of the spatial behaviour investigated in this paper include the equilibrium path, the particle orbit, and the geometric attenuation of the activated Rayleigh waves. The results presented in this paper can provide some guidelines for developing new inverse mathematical models and algorithms.     

Application of a nondestructive method to evaluate the active layer in a cold region

To provide a safe transportation system in an extremely cold region,evaluation needs to be conducted of the thickness and the volumetric water content of the active layer,as they significantly affect frost heave.The objective of this study was to evaluate the dielectric constant(κ)of the active layer using ground-penetrating radar(GPR)and a dynamic cone penetrometer(DCP);this evaluation was then used to estimate the thickness and the volumetric water content of the active layer.A field located in midwest Alaska was selected as the study site.A GPR survey and two DCP tests were conducted on the surface of the ground,and the ground temperature was measured.From the GPR survey,travel times of the electromagnetic wave in the active layer were obtained.In addition,the thickness of the active layer was determined by using the dynamic cone penetration index(DCPI)and ground temperature.By using the travel time and travel distance of the electromagnetic wave in the active layer,dielectric constants were calculated as 26.3 and 26.4 for two DCP points.From the mean dielectric constant,the volumetric water content was estimated to be 40%~43%,and the thickness of the active layer was evaluated along the GPR survey line.The spatial-scaled GPR image showed that the thickness of the active layer varied from 520 mm to 700 mm due to the presence of a puddle,which accelerated the heat exchange.The results show that evaluation of the dielectric constant using the GPR survey and the DCP test can be effectively used to estimate the thickness and the volumetric water content of the active layer.     

ON THE PHYSICS OF FLOW-DRIVEN SEDIMENTS (BED-LOAD)

l PROBLEMS AND AlMSSediments may be transported close to the bed, rolling and sliding, as we1l as susPended in the flow. Forvarious reasons the theoretical treatment of the bed-load problem has been exceptionally difficult. Noanalytical solution had been fOund uP to now, beginning with Du Buat (l786), Huebbe (l86l) and DuBoys (I 879). Since the aPProach of Du Boys numerous new attemPts have been catried out, mostly of anempirical nature. Consequently they are not generally valid an…     

An assessment model for the fate and environmental effects of offshore drilling mud discharges

The benthic boundary layer transport (bblt) model was developed to assess potential impact zones from drilling mud discharges from offshore oil and gas drilling. The model focuses on the drift, dispersion and concentration levels of the suspended fraction of the drilling mud fines in the benthic boundary layer with the assumption of a spatially homogeneous environment. The current version of the model includes a wave boundary layer, a breakup module for drilling mud flocs, a dose–response module for scallops, and a graphical user interface (GUI). The GUI was written in Java which makes the code largely platform independent. Simulations of suspended barite concentration near Sable Island on the Scotian Shelf during drilling in the fall of 1999 reproduce the very low concentrations (generally less than 1 μg L⁻¹) observed during the Environmental Effects Monitoring program. However, the simulations also exhibited concentrations in excess of the no-effects concentration for scallops (100 μg L⁻¹) prior to the sampling program. The model estimates that the potential impact on scallops in the vicinity of the drilling is a few days of lost growth over scales of a few kilometers.     

定量诊断2008年初南方罕见冰冻雨雪天气

根据NCEP/NCAR逐日再分析资料和每三小时一次的TRMM 3B42降水资料,利用改进后的局地经向环流线性诊断模式(不用地转风近似而用旋转风估算水平环流经向分量),定量分析了2008年初我国南方地区局地经向环流的垂直分量(-ωMC)的演变情况.结果表明:当我国南方地区发生强降水时,局地经向环流的强上升支气流((-ωM...     

初始误差对双环流变异可预报性的影响

使用球坐标下1.5 层约化重力浅水模式模拟海洋风生双环流, 结果显示双环流射流存在拉伸模态和收缩模态间的年际变化。以双环流从拉伸模态向收缩模态的转变过程为背景场, 利用条件非线性最优扰动(CNOP)方法, 考察初始误差对双环流变异可预报性的影响, 得到两类初始误差: 全局CNOP型和局部CNOP(LCNOP)型, 两类初始误差对双环流变异的影响几乎相反。通过考察误差发展, 发现在射流从拉伸模态向收缩模态转变过程中, CNOP 型初始误差使射流弯曲程度变大, 并在预报时刻导致涡脱落; 而LCNOP 型初始误差则使射流弯曲程度变小。相比LCNOP, CNOP 型初始误差引起更大预报误差, 导致双环流变异的预报技巧下降更多。两类误差得到较大发展的区域可能存在正压不稳定, 使误差能够不断从背景场吸收能量进而得到快速发展。给出了两类使双环流变异预报技巧下降最大的初始误差, 在实际的数值预报中减少这两种类型的误差, 将有助于提高双环流变异的预报技巧。     

Roughness length and drag coefficient at two MONTBLEX-90 tower stations

Using MONTBLEX-90 mean velocity data, roughness lengths and drag coefficients are estimated at Jodhpur and Kharagpur. At Jodhpur, since the surface is not uniform the roughness length is estimated separately in three different subsectors within the range of prevailing wind directions and averages to 1.23 cm in the sector between 200° and 230° which is relatively flat with no obstacles on the ground. At Kharagpur, where the terrain is more nearly homogeneous, the average value (for all prevailing wind directions) is 1.94 cm. The drag coefficient C_D at Jodhpur shows variation both with the roughness subsector and with wind speed, the average over all directions increasing rapidly as themean wind speed Ū₁₀ at 10m height drops according to the power lawC _D = 0.05 Ū ₁₀ ^t-1.09 in trie range 0.5 < Ū₁₀ < 7 m s⁻¹. At Kharagpur, the drag coefficient is smaller than at Jodhpur by nearly 50% for the same range of wind speeds (> 3 ms⁻¹).     

松辽盆地南部姚家组沉积特征及铀成矿条件

松辽盆地是我国东北地区大型的含油气产铀盆地,其盖层中的上白垩统姚家组在盆地南部广泛分布,埋深适中;沉积体系以冲积平原、辫状河、三角洲、湖泊等为主,具有稳定的泥-砂-泥地层结构;砂体厚度稳定,分布范围广,有机质和铀含量高;沉积期的温热-半温热古气候有利于富铀建造的形成。姚家组补-径-排水动力体系完善,后生改造条件较佳。综合分析结果显示,该组具有较好的铀成矿潜力,是松辽盆地南部找铀矿的主攻目的层位。