2018年北京“7.16”暖区特大暴雨特征及形成机制研究     

雷蕾  邢楠  周璇  孙继松  翟亮  荆浩  郭金兰 《气象学报》2020,78(1):1-17

利用京津冀区域加密自动气象站、SA多普勒天气雷达、L波段风廓线雷达、NCEP 0.25° 再分析资料及0.03° 高分辨率地形资料研究了北京2018年7月15—16日暖区特大暴雨特征和形成机制。结果表明:（1）这次暖区特大暴雨发生在副热带高压边缘的暖气团（θ_se高能区）中,无明显冷空气强迫,斜压性弱,有丰沛的水汽,850 hPa以下出现强水汽辐合。（2）暴雨的中尺度对流系统发展有3个过程:带状对流建立和局地强雨团影响、北京北部“列车效应”南部雷暴冷池出流造成对流加强和移动、平原地区线状对流重建。（3）暴雨发生前,低层西南风出现风速脉动,低空急流建立。首先在2500—3500 m高度形成低空急流,2 h后2500 m以下风速显著增大,5 h后急流厚度由边界层伸展到700 hPa。急流出口区降压,低层出现气旋性风场或切变,有利于垂直上升运动发展,触发和加强对流。（4）西南低空急流暖湿输送导致高温、高湿、高能的对流不稳定层结反复重建,这是对流发展加强的重要原因。（5）地面辐合线是对流触发并逐渐组织成带状对流系统的关键影响因素。地面辐合线方向、低空急流轴、回波移动方向三者几乎重叠是造成对流后向传播和“列车效应”的有利条件。（6）太行山和燕山地形对对流触发和暴雨增幅有重要影响。北京最大雨强≥40 mm/h站点中的77.4%位于西南部和东北部200—600 m海拔高度处。偏东风在华北西部太行山局地迎风坡触发对流,西南低空急流在北京北部迎风坡和喇叭口地形处辐合和抬升更为显著,造成局地特大暴雨。   相似文献   

“白鹿”台风(1911)残涡造成广西大范围暴雨成因分析     

陈见  覃月凤  翟舒楠  董良淼  肖志祥 《气象研究与应用》2020,(1):65-69

利用常规气象资料及EC再分析、卫星云图、雷达、中尺度自动站等资料,采用天气动力诊断分析方法,对"白鹿"台风(1911)残涡造成广西大范围暴雨的成因进行分析。结果表明,"白鹿"台风残涡暴雨是在有利的高低空环流形势和强水汽辐合条件共同作用下造成的。有利的环流条件使停编后的"白鹿"残涡强度维持、加强,卫星云图显示"白鹿"南半环云系发展旺盛、密实,雷达回波显示残涡螺旋云带的前端有新生对流发展、传播,从而造成广西大范围暴雨发生。  相似文献   

Transient upwelling in the central Baltic Sea     

W. Fennel  H. RadtkeM. Schmidt  T. Neumann 《Continental Shelf Research》2010

The paper presents a theoretical study to explain the regular occurrence of a cold water upwelling cell at the southern east coast of the Gotland island in the central Baltic Sea. While for a circular island up- and downwelling patterns would rotate around the island, the responses around the elongated Gotland island with narrow tips at its southern and northern ends are different. The study uses the example of the response of a coastal ocean to a wind band to develop an understanding of important aspects of generation of Kelvin waves and how the waves change the response patterns.  相似文献   

Flow in a tightly curving meander bend: effects of seasonal changes in aquatic macrophyte cover     

I. Schnauder  A. N. Sukhodolov 《地球表面变化过程与地形》2012,37(11):1142-1157

The effects of aquatic macrophytes on flow and turbulence were studied in a tightly curving meander bend. Three field measurement campaigns were carried out within a one year period to capture effects of seasonal changes in macrophyte cover. They comprised three‐dimensional velocity measurements and mappings of vegetation cover and bathymetry. Flow accelerates and converges over the run into an axial pool in a jet‐like flow pattern bordered by outer and inner bank flow separation zones. The jet and widening of the cross‐section anticipate helical flow until the second half of the bend, where an asymmetric pool developed. Submerged vegetation at the riffles preserves the jet at much lower discharges during the summer period by concentrating high momentum fluid near the surface. Plants locally modify the velocity and stress patterns, reduce bed shear stresses, create zones of fine sediment accumulation and reinforce the bed and banks with roots and rhizomes. Plant patches colonising the banks and the point bar confine secondary flow cells laterally and affect shape and magnitude of the transverse flow profiles near their edges. The morphology of the bend was very stable over the observation period and neither bank erosion nor pool scouring occurred. However, fine sediments accumulate within vegetation patches and in the recirculation zones while the remaining open areas tend to erode slightly. With the decay of macrophytes in winter, sediment accumulations are mobilised again and the bathymetry levels, supporting cyclic models of morphologic change in vegetated bends. In the second part of the paper, semi‐empirical models for the three predominant flow types were tested and discussed; velocity and stress models of vegetated mixing layers and plane turbulent jets, and Rozovskii's model for the transverse flow in bends. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

水射流辅助PDC刀具切割岩石的力学分析     

卢义玉  陆朝晖  李晓红  康勇  赵瑜 《岩土力学》2008,29(11):3037-3040

通过对水射流辅助PDC刀具切割破碎岩石的力学分析,定量地确定出水射流对机械刀具受力的作用。试验研究表明,水射流辅助刀具切割岩石时刀具受力随切割深度的增加而线性增加;水射流布置在刀具底部后方,并偏离刀具铅垂中性面适当位置辅助刀具破岩时,刀具受力可减少30 %～50 %,并且刀具力的减少率几乎不受切割深度变化的影响。  相似文献   

Multiphase flow above explosion sites in debris-filled volcanic vents: Insights from analogue experiments     

Pierre-Simon Ross  James D.L. White  Bernd Zimanowski  Ralf Büttner 《Journal of Volcanology and Geothermal Research》2008

Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in unconsolidated material, no details are available regarding the structure of the disturbed debris between the explosion site and the surface. Field studies of diatreme deposits reveal cross-cutting, steep-sided zones of non-bedded volcaniclastic material that have been inferred to result from sedimentation of material transported by “debris jets” driven by explosions. In order to determine the general processes and deposit geometry resulting from discrete, explosive injections of entrained particles through a particulate host, we ran a series of analogue experiments. Specific volumes of compressed (0.5–2.5 MPa) air were released in bursts that drove gas-particle dispersions through a granular host. The air expanded into and entrained coloured particles in a small crucible before moving upward into the host (white particles). Each burst drove into the host an expanding cavity containing air and coloured particles. Total duration of each run, recorded with high-speed video, was approximately 0.5–1 s. The coloured beads sedimented into the transient cavity. This same behaviour was observed even in runs where there was no breaching of the surface, and no coloured beads ejected. A steep-sided body of coloured beads was left that is similar to the cross-cutting pipes observed in deposits filling real volcanic vents, in which cavity collapse can result not only from gas escape through a granular host as in the experiments, but also through condensation of water vapour. A key conclusion from these experiments is that the geometry of cross-cutting volcaniclastic deposits in volcanic vents is not directly informative of the geometry of the “intrusions” that formed them. An additional conclusion is that complex structures can form quickly from discrete events.  相似文献   

Global 3‐D solar‐type star‐disc dynamo systems: I. MHD modeling     

B. von Rekowski  N. Piskunov 《Astronomische Nachrichten》2006,327(4):340-354

We have carried out global three‐dimensional magnetohydrodynamic simulations of the star‐disc interaction region around a young solar‐type star. The magnetic field is generated and maintained by dynamos in the star as well as in the disc. The developing mass flows possess non‐periodic time‐variable azimuthal structure and are controlled by the nonaxisymmetric magnetic fields. Since the stellar field drives a strong stellar wind, accretion is anti‐correlated with the stellar field strength and disc matter is spiraling onto the star at low latitudes, both contrary to the generally assumed accretion picture. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

High resolution imaging of parsec-scale jets: the impact of the VSOP observations     

A. P. Lobanov  T. P. Krichbaum  A. Witzel  J. A. Zensus 《New Astronomy Reviews》1999,43(8-10)

Resolution improvements achieved with the ongoing space VLBI mission VSOP provide an excellent opportunity for studying compact, parsec-scale jets in active galactic nuclei. Visibilities on space baselines contain structural information that cannot be recovered by super-resolving ground-array data at the same frequency. We illustrate this by discussing the results of recent VSOP observations of parsec-scale jets in 0836+710 and 3C273.  相似文献   

An accretion-jet model for 3C 84: Interpreting the spectral energy distribution and Faraday rotation measure     

Jianchao Feng  Xiaowen Wang  Rui Jing 《Astronomische Nachrichten》2024,345(2-3):e230175

3C 84 is a well-known supermassive black hole that can be used to explore jet and accretion physics. In this work, we model the multiwavelength spectral energy distribution (SED) of the 3C 84, and find that the SED is difficult to fit with pure advection dominated accretion flow (ADAF) or pure jet model. Using a coupled ADAF-jet model to fit the SED of 3C 84, it is found that the radio emission and the millimeter emission can be naturally reproduced by the synchrotron radiation of nonthermal electrons in the jet, and that the X-ray emission may predominantly come from inverse Compton radiation from electrons in ADAF. According to the Rotation Measure (RM) obtained by the polarization observation, we consider the possible location of the polarizing source and found that the calculated RM in the jet is roughly consistent with the observational constraints. These results will help us better understand jets produced by black holes.  相似文献   

基于多源资料的乌鲁木齐市两次极端短时强降水对比分析          下载免费PDF全文

张金霞  张云惠  于碧馨  芒苏尔.艾热提 《沙漠与绿洲气象(新疆气象)》2021,15(3):10-19

利用常规观测、区域自动站、FY-2G气象卫星、多普勒雷达、风廓线雷达及NCEP 1°×1°再分析等多源资料,分析乌鲁木齐2015年6月9日和27日(分别简称"6·09"和"6·27"过程)两次极端短时强降水成因。结果表明:(1)"6·09"过程是在高压脊前西北气流下,由700、850 hPa双低空急流耦合触发,配合强低层风切变,低层水汽快速聚集造成的局地性强对流天气,TBB最低为-52℃,雷达回波为典型的"列车效应",强回波达55 dBZ。"6·27"过程是在中亚低涡背景下,西南、偏西、偏东三条水汽路径使得整层增湿,配合持续时间较长的弱低层风切变,是系统性降水中的强对流天气,TBB最低为-44℃,雷达回波为混合性降水回波中分散的对流单体,强回波达50d BZ;此外",6·09"过程热力不稳定条件较好。(2)风廓线雷达显示两次过程低层均存在垂直风切变,折射率结构常数均在强降水时迅速增大并维持高值,随着降水减弱迅速减小;两次过程均发生在中β尺度对流云团TBB梯度最大处。(3)雷达回波均属于低质心对流风暴,且地面均配合有中γ尺度气旋性风场辐合或切变。  相似文献