一次东北冷涡下槽后强风与飑线后向入流演变及成因分析     

张乐楠  丁治英  王咏青  张璐 《气象科学》2019,39(4):488-501

本文利用NCEP分析资料、多普勒雷达观测资料、常规气象观测资料以及数值模拟结果,对2016年7月30日发生在华北、辽宁附近的一次强飑线过程中后向入流的演变及成因进行研究。结果表明,此次飑线发生在中纬度新生冷涡槽前,低层有水汽辐合区和地面辐合线对应,且过程中伴有较强的对流有效位能释放。飑线后部中层(冷涡槽后)一直存在α中尺度西风大值带,此大风速带造成了上下层相反的水平涡度,并形成喇叭形环流结构,该结构不同于经典飑线结构。飑线后部水平方向上水平涡度分布不均匀,并形成水平涡度旋度上正下负的分布,即导致中层强风区上部上升运动、下部下沉运动,该下沉运动引发飑线中的后向入流和低层强风速带形成。在中层,飑线的后部边缘始终有较强的风速大值带伴随飑线的发展,该大值带的形成与对流强弱和非热成风涡度有关,对流过程中低层非热成风涡度为负,中上层非热成风涡度为正,导致飑线后部中层西风加速和低层西风减速,有利于后向入流的发展和飑线的维持,当对流减弱时,非热成风涡度与后向入流均减弱。文中给出了后向入流形成演变的概念模式。  相似文献   

长江漫滩区深大异形基坑施工对紧邻特大型桥梁影响及变形控制研究     

史建升  徐源  李慧  阎长虹  侯珏  俞良晨  赵华新  崔王洪  徐成华  刘刚 《地质论评》2024,70(1):2024010005-2024010005

随着地下空间资源的开发利用,越来越多深基坑呈现出开挖深、规模大、形状不规则等特点,其支护结构设计复杂,施工难度大,具有明显的空间效应。本文以南京地铁某基坑工程为例,分析基坑施工对邻近桥梁的影响。其场区位于长江下游漫滩相二元结构地层分布地段,上部软土层厚度大,下部承压含水层地下水位高、水量丰富,地质条件复杂,该基坑为典型的深大异形基坑,距离某大桥的双曲拱引桥仅为7. 2 m,由于之前桥梁已遭受其他地下工程施工产生的较大变形,所以后续工程对其影响变形控制要求极高。为此,该车站基坑支护结构设计基于地下空间实际功能采用设置分隔墙分区开挖及MJS超深工法墙综合变形控制方案。本文通过有限元数值模拟计算,开展复杂环境下基坑开挖引起的围护结构及桥梁桩基的变形预测分析,计算结果显示,该深大狭长异形基坑开挖对邻近桥梁沉降变形影响显著,通过设置分隔墙分区开挖及MJS工法墙进行变形控制,能够较好地控制基坑的空间效应,减少“长边效应”、“异形效应”等对桥梁沉降变形的影响。通过现场基坑开挖过程实际监测结果,验证这一综合变形控制方案的可行性。该研究成果对于类似复杂地质条件下深大狭长异形基坑的支护及施工设计具有很好的借鉴意义。  相似文献   

The interaction of two asymmetric quasi-geostrophic vortex patches     

M. M. Jalali 《地球物理与天体物理流体动力学》2013,107(6):375-401

ABSTRACT

Herein we study the general interaction of two vortex patches in a single-layer quasi-geostrophic shallow-water flow. Steadily-rotating equilibrium states are found over a wide parameter space spanning the Rossby deformation length, vortex area ratio, potential vorticity ratio, and gap between their innermost edges. A linear stability analysis is then used to identify the critical gap separating stable and unstable solutions, over the entire range of area and potential vorticity ratios, and for selected values of the Rossby deformation length. A representative set of marginally unstable equilibrium states are then slightly perturbed and evolved by an accurate contour dynamics numerical algorithm to understand the long-term fate of the instabilities. Not all instabilities lead to vortex merger; many in fact are characterised by weak filamentation and a small adjustment of the vortex shapes, without merger. Stronger instabilities lead to material being torn from one vortex and either wrapped around the other or reduced to ever thinning filamentary debris. A portion of the vortex may survive, or it may be completely strained out by the other.  相似文献   

A note on some early radiosonde temperature observations in the Antarctic lower stratosphere     

H. R. Phillpot 《Pure and Applied Geophysics》1989,130(2-3):171-180

The behaviour of the Southern Hemisphere stratosphere has attracted considerable interest, and been compared with the Northern Hemisphere, since the International Geophysical Year (1957–58) when the sudden (explosive or accelerated) springtime warming phenomenon in the Antarctic was first observed. Over the years studies of upper air temperature and wind observations have been made, principally through the spring months when the polar vortex breakdown occurs, utilising both ground-based (rawinsonde, rocket) and more recently, satellite-derived data. Although the radiosonde-derived temperature data are limited both by the number of reporting stations, and the practical difficulty of securing observations much above the 100 hPa level, useful records exist from 1956 or 1957. These have shown that in the 1959 southern spring, the lower stratosphere was relatively colder, and the warming rate through the season was essentially more regular, with little evidence of the marked but short-lived temperature fluctuations usually found. Similar, but not quite such wide-spread conditions occurred again in the 1961 spring. In another study, 30 hPa temperature fields over the Antarctic continent, which could be drawn for the 1967 spring, showed the complexity of the polar vortex breakdown. These features are recalled because extension of the 100 hPa springtime temperature series for the Australian Antarctic station at Casey (66.3°S, 110.5°E) shows that in 1985 and part of 1986, the temperature behaviour there was similar to, but not quite so extreme as that which occurred at Mirny (66.5°S, 93.0°E) in 1959.  相似文献   

Settling-velocity distributions and sorting processes on a longitudinal dune: A case study     

Daniel Hartmann  Christian Christiansen 《地球表面变化过程与地形》1988,13(7):649-656

The processes acting on a longitudinal dune are inferred from the response in the area size-sorting characteristics of the sediment of the active layer. The sediment size distributions are determined by settling and are best described by a log-hyperbolic model which provides the most information on size-sorting processes. Size-sorting characteristics are markedly different across the low round-crested part of the dune from cross-sections of the high more sharp-crested part. This results in changes in textural parameters along the lee-side consistent with changes in the lee-side separation vortex. This is the first time that the effect of wind speed up on the lee-side is observed to be reflected in the sediment; it can only be detected with the very sensitive log-hyperbolic parameters.  相似文献   

梅雨锋次天气尺度涡旋旋转风和辐散风动能收支   总被引：2，自引：3，他引：2  

汪钟兴  刘勇 《高原气象》1994,13(1):28-34

本文选取１９９１年７月５日２０：００－６日２０：００梅雨锋上移动性次天气尺度涡旋引起的长江中下游特大暴雨为实例。采用准拉格朗日球坐标系的旋转风和辐散风动能方程，计算得到次天气尺度涡旋发展和成熟两个阶段对流层各层旋转风动能和辐散风动能的收支特征为：在对流层高层（１００－４００ｈＰａ）两个阶段的旋转风动能源汇相同，辐散风动能源汇有异，即水平动能通量项和“摩擦”项符号相反；在中层（４００－７００ｈＰａ）  相似文献   

大气中低频重力波指数与西南低涡发展及其暴雨的关系   总被引：1，自引：0，他引：1  

马振锋 《高原气象》1994,13(1):50-56

采用低频重力波指数法，对西南低涡发展演变及其暴雨强度，落区进行了诊断分析和预测。结果指出：（１）低频重力波指数Ｃｐ，Ｃｉ对西南低涡的发展及其暴雨强度，落区都有一定的预测意义，其预见期可达２４小时以上；（２）低频重力波指数随时间变化与西南低涡发有较好的对应关系；（３）低频重力波指数的大小与西南低涡暴雨强度相联系；（４）西南低涡暴雨落区通常发生在Ｃｐ，Ｃｉ指数的最大负值区内和Ｃｐ等值线梯度最大的区域。  相似文献   

The interannual variability of mid-latitude meridional circulation and its teleconnection with Indian monsoon activity     

J. Chattopadhyay  R. Bhatla 《Journal of Earth System Science》1994,103(3):369-382

The statistical relationship between the summer monsoon rainfall over all India, northwest India and peninsular India, onset dates of monsoon and the index of mid latitude, (35° to 70°N) meridional circulation at 500 hPa level over different sectors and hemisphere based on 19 years (1971–1989) data, have been examined. The results indicate that (i) the summer monsoon rainfalls over all India, northwest India and peninsular India show a significant inverse relationship with the strength of meridional index during previous January over sector 45°W to 90°E. (ii) The summer monsoon rainfalls over all India and peninsular India show a significant inverse relationship with the strength of meridional index during previous December over sector 90°E to 160°E, (iii) The summer monsoon rainfall over northwest India shows a significant direct relationship with the meridional index during previous May over sector 160°E to 45°W. Significant negative relationships are also observed between the meridional circulation indices of previous October (sector 3 and 4), previous December (sectors 1, 3 and 4), previous winter season (sector 3 and 4) and the onset dates of summer monsoon over India. The meridional circulation index thus can have some possible use for long range forecasting of monsoon rainfall over all India, northwest India and peninsular India, as well as the onset dates of monsoon.  相似文献   

CONTOUR DYNAMICS FOR VORTEX MOTION INFLUENCED BY THE CORIOLIS FORCE^*          下载免费PDF全文

Luo Zhexian 《Acta Meteorologica Sinica》1994,8(1):60-71

The computational formulae are given for single-contour constant-value vortex motion influenced by the Coriolis force in the framework of contour dynamics,by which four numerical computations are performed,the result exhibiting their validity.  相似文献   

A CASE OF MESOSCALE CONVECTIVE COMPLEX EVOLVING INTO A VORTEX   总被引：1，自引：0，他引：1       下载免费PDF全文

陶祖钰  王洪庆  白洁  朱文琴  石定朴  杨红梅 《Acta Meteorologica Sinica》1995,(2)

A case of mesoscale convective complex(MCC)which evolved into a vortex is documented in this paper.As theMCC entered into the dissipating phase,a well-defined spirally banded structure became visible in the satellite image.The blackbody temperature(TBB)of the residual cold-cloud-shield indicates the vortex existed in the layer from 400 to250 hPa.According to the upper air analysis,the upper level vortex was an anticyclone.The MCC-generated vortex wasvisualized in the satellite images because it was located in the subtropical high where the wind field was very weak.  相似文献