惯性稳定性在伴有高低空急流的暴雨中的作用   总被引：5，自引：0，他引：5  

张文龙  周军 《南京气象学院学报》2003,26(4):473-480

通过对低空西南急流左前方和高空偏北大风轴右后方的惯性稳定性和对称稳定性的理论分析和实例计算，表明：低空急流左前方惯性稳定度大值区的存在，有利于低层湿热能量的积累，使低层倾斜对流的不稳定发展更多期望于条件性对称不稳定或对流不稳定；高空偏北大风轴(西风急流)的存在，是其右后方(右侧)出现对称不稳定的有利条件，高空相对容易出现干对称不稳定；惯性稳定性的作用，使低层的倾斜对流更偏向于垂直方向，有利于对流发展，使高层的倾斜对流更偏向于水平方向，有利于高层辐散。  相似文献   

On the Validity of the Boussinesq Approximation for the Elder Problem     

K. Johannsen 《Computational Geosciences》2003,7(3):169-182

The Elder problem is an example of a density driven flow, motivated by experiments of a thermally driven convection in porous media. It is a mathematical benchmark problem used for code verification of density driven flow simulators and comparison of issues related to its numerical treatment. Its bifurcation diagram with respect to the Rayleigh number is investigated on a hierarchy of uniformly refined grids. Eleven stationary solutions are shown to exist for the Elder problem. Similar solutions can be found using the Boussinesq approximation. Despite this similarity the corresponding bifurcation diagrams are shown to be topologically not equivalent. This gives rise to serious doubts on the validity of Boussinesq approximation for this model problem. Grid convergence is investigated for the numerically obtained solutions.  相似文献   

Simple features of mantle-wide convection and the interpretation of lower-mantle tomograms     

Norman H. Sleep 《Comptes Rendus Geoscience》2003,335(1):9-22

Simple fluid dynamic constraints aid in the interpretation of lower mantle tomograms. The geothermal gradient away from slabs and plumes is subadiabatic between the upper (lithosphere) and lower (D″) boundary layers by ～400 K. Slabs widen proportionally with the square root of the viscosity as they sink through the lower mantle. The time scale for the persistence of slab graveyards at the base of the mantle is comparable to the time for plate motions to reorganize ～120–200 Myr. At most a few starting plume heads currently exist in the lower mantle. Tomographic inversions may include more sophisticated numerical-modeling versions of these constraints.  相似文献   

青藏高原东缘地壳运动与深部过程的研究   总被引：26，自引：9，他引：26       下载免费PDF全文

熊熊  滕吉文 《地球物理学报》2002,45(4):507-515

由于青藏高原东部地区记录了高原约50 Ma演化历史中物质东流的构造史,因此受到地学界的广泛重视. 现代大地测量与地质研究结果给出了该区现代地壳运动的图像,为地球动力学数值模拟提供了重要的边界约束条件. 利用重力异常计算的高原及邻区地幔对流应力场与地表地壳运动格局的明显差异表征了高原东部地壳与地幔物质的运动解耦. 基于随深度变化地壳蠕变率的动力学模拟结果显示,高原东部地壳增厚与高原内部存在很大差异,高原东部地壳增厚主要表现为下地壳的增厚,并且地幔形变过程与地表变化也不一致,同样显示出地壳、地幔运动的解耦. 研究表明,下地壳低强度分布可能是导致这种解耦的重要原因,而了解高原东部地壳及上地幔物理力学性质对我们认识高原物质东流至关重要.  相似文献   

南宁市强对流暴雨天气雷达回波类型分析     

周能  丁溢锋  陆春菊 《气象研究与应用》2002,23(4):23-26

将南宁市强对流暴雨天气的雷达回波分成四种类型,对利用雷达回波特征制作强对流暴雨天气预报提供帮助。  相似文献   

上海“0185”特大暴雨过程天气形势分析   总被引：10，自引：2，他引：10  

姚祖庆 《气象》2002,28(1):26-29

对上海2001年8月5-6日特大暴雨的天气形势做了详细分析指出，在副高内由东风系统发展起来的热带低压由于结构深厚得以在强大副高内稳定维持，而副热带高压断裂的形势变化至关重要，由于西环副高北侧的西北偏西气流渗入，对热带低压内强对流迅速、持久发展起了重要作用，同时东环副高减退，又成为热带低压路径突然东折的主要因素。  相似文献   

Convective Redistribution of Ozone and Oxides of Nitrogen in the Troposphere over Europe in Summer and Fall     

Øystein Hov  Frode Flatøy 《Journal of Atmospheric Chemistry》1997,28(1-3):319-337

The fluxes of ozone and NO_x out of the atmospheric boundary layer (ABL) over Europe are calculated in a mesoscale chemical transport model (MCT) and compared with the net chemical production or destruction of ozone and the emissions of precursors within the ABL for two 10 days' periods which had quite different synoptic situations and levels of photochemical activity (1–10 July 1991 (JUL91) and 26 October–4 November 1994 (ON94)). Over the European continent, about 8% of the NO_x emissions were brought from the ABL to the free troposphere as NO_x, while about 15% of the NO_x emissions were brought to the free troposphere as NO_y–NO_x, i.e. as PAN or HNO₃. The convection dominates over the synoptic scale vertical advection as a transport mechanism both for NO_x and NO_y out of the boundary layer in the summertime high pressure situation (JUL91), while in the fall situation (ON94) the convective part was calculated to be the smallest. NO_x was almost completely transformed to NO_y–NO_x or removed within the ABL. Also for NO_y the major part of the atmospheric cycle is confined to the ABL both for JUL91 and ON94. The vertical transport time out of the ABL is of the order of 100h both for the total model domain and over the European continent. The net convective exchange of ozone from the ABL is not a dominant process for the amount of ozone in the ABL averaged over 10 days and the whole domain, but convection reduces the maximum ozone concentration in episodes significantly. The ozone producing efficiency of NO_x is calculated to increase with height to typically 15–20 in the upper half of the troposphere from around 5 in the ABL, but in the middle free troposphere the concentration of NO_x is often too low to cause net chemical formation of ozone there.  相似文献   

登陆台风不连续北跳与暴雨的数值模拟研究          下载免费PDF全文

丁治英  陈久康 《应用气象学报》1997,8(1):44-52

利用MM4（PSU/NCAR）模式，对1992年8月31日20时～9月1日20时登陆台风暴雨过程进行了数值试验研究。结果表明；登陆台风的不连续北跳与西风槽和积云对流潜热反馈有关。倒槽南部雨区内积云对流的发展加大了对台风倒槽内的水汽、动量、热量等输送，使倒槽内降水增幅。积云对流潜热反馈对高低空急流以及台风的移动都有很大的影响。  相似文献   

Simultaneous observations at different altitudes of ionospheric backscatter in the eastward electrojet     

S. E. Milan  M. Lester 《Annales Geophysicae》1997,16(1):55-68

A common feature of evening near-range ionospheric backscatter in the CUTLASS Iceland radar field of view is two parallel, approximately L-shell-aligned regions of westward flow which are attributed to irregularities in the auroral eastward electrojet region of the ionosphere. These backscatter channels are separated by approximately 100–200 km in range. The orientation of the CUTLASS Iceland radar beams and the zonally aligned nature of the flow allows an approximate determination of flow angle to be made without the necessity of bistatic measurements. The two flow channels have different azimuthal variations in flow velocity and spectral width. The nearer of the two regions has two distinct spectral signatures. The eastern beams detect spectra with velocities which saturate at or near the ion-acoustic speed, and have low spectral widths (less than 100ms^–1), while the western beams detect lower velocities and higher spectral widths (above 200ms^–1). The more distant of the two channels has only one spectral signature with velocities above the ionacoustic speed and high spectral widths. The spectral characteristics of the backscatter are consistent with E-region scatter in the nearer channel and upper-E-region or F-region scatter in the further channel. Temporal variations in the characteristics of both channels support current theories of E-region turbulent heating and previous observations of velocity-dependent backscatter cross-section. In future, observations of this nature will provide a powerful tool for the investigation of simultaneous E- and F-region irregularity generation under similar (nearly co-located or magnetically conjugate) electric field conditions.  相似文献   

Effect of a Viscosity Interface at 1000 km Depth on Mantle Circulation     

ČIžková  Hana  Čadek  Ondŕej 《Studia Geophysica et Geodaetica》1997,41(3):297-306

We present the preliminary results of axisymmetric numerical simulations of thermal convection in the mantle with a phase transition boundary at 660 km depth and a viscosity interface at 1000 km depth. The results, obtained for Ra = 2 × 10 ⁶ , are compared with the case when both the phase and the viscosity boundaries are located at the same depth of 660 km.  相似文献