华南暖区暴雨事件的筛选与分类研究

利用逐小时降水资料,采用客观方法对1982~2015年华南地区暖区暴雨进行了筛选和分类研究。主要结果如下:华南区域暖区暴雨事件共计177例,暖区暴雨占筛选的暴雨事件的16.86%,表明暖区暴雨是华南非常重要的降水过程。暖区暴雨主要出现在4~7月,6月份最多,平均持续11.58 h。暖区暴雨事件发生位置主要集中在广东、广西的沿海地区和粤北山区,有四个降雨中心。产生华南暖区暴雨的天气形势主要有四类,切变线型、低涡型、南风型和回流型,不同类型的暖区暴雨对华南地区的内陆和沿海的作用不同,且南风影响下的暖区暴雨发生频率较高,影响较大,是一类较为重要的暖区暴雨。     

HHT技术探测Slichter模三重谱线的研究

探测Slichter模态三重分裂可有效约束内核密度、内核半径及内外核边界密度跳跃。虽然Smylie(1992)声称探测到了Slichter模态三重分裂,但至今未被国际学术界公认。本文结合一个实验算例,阐述了Hilbert-Huang变换(HHT)分析方法的核心思想,并将该方法应用于探测Slichter模三重分裂谱线的研究。我们选取了全球分布的8个台站连续记录两年的小时间隔超导重力数据,进行了潮汐和气压改正后,将它们叠加获得重力残差;然后对重力残差作HHT分析,得到能量谱,进而选出了12种可能的谱峰组合,其中两组结果与Smylie的结果很接近,且本文得到的谱峰分裂相比于Smylie的结果具有更好的对称性。     

哈尔滨机场冷涡雷暴预报方法初探

本文通过用数值预报产品对冷涡雷暴分析,得出数值预报的形势场、抬升指数、K指数、垂直速度等,对提前预报冷涡雷暴有很好的指示作用。结合卫星云图、雷达回波图,能更好的监控冷涡雷暴的发展演变,为飞行安全提供有力保障。     

Some aspects of vortices in rotating stratified fluids

Summary Ideas concerning the overturning of unstably stratified, rotating fluids are explored using potential vorticity.A set of equations governing axi-symmetric flow in a quasi-Boussinesq system are found based on the gradient wind approximation, and a transformation analogous to that developed byHoskins [6] is used.The time-development of a linear, thermally unstable vortex under the action of Ekman pumping is studied with these equations. The changing radial scale during amplification of the vortex is well represented.Finally, some exact steady vortex states for stably stratified fluids are found and their possible relevance to atmospheric vortices is discussed.     

2003年淮河汛期一次中尺度强暴雨过程的诊断分析和数值模拟研究

2003年7月4—5日淮河流域发生了一次中尺度强暴雨过程,致使淮河洪水泛滥。这次暴雨过程由中尺度对流系统(MCS)以及因其发展而产生的低涡造成。通过对此次过程的诊断分析和新一代细网格WRF中尺度预报模式的数值模拟,研究了这次过程发生发展的机制。模拟结果较好地描述了本次暴雨及中尺度系统发生、发展的时空演变过程。分析结果表明:此次移动性暴雨过程的前期由不断向东移动发展的MCS造成,后期降水则由低涡切变线产生的中尺度低涡引起。同时,副热带高压明显偏西偏北,并维持较长时间,造成雨带一直维持在淮河流域。高层辐合中心的加强使低空急流不断增强,低空急流的增强进而引起低层辐合的加强,而低层辐合的加强以及上升运动的潜热释放导致低涡的发生,低涡形成及形成后移动缓慢,造成了淮河流域的大暴雨。高层中尺度辐散区的抽吸对低层中尺度涡旋的发生发展起到了促进和加强的作用。低层的中尺度辐合场和高层的中尺度辐散场的发展与耦合对中尺度系统的发展有很好的预示作用。低层中尺度辐合区的减弱预示着系统的衰减,西南偏西的中层相对干冷空气侵入并在梅雨锋前缘下沉促进了系统的衰减。     

Some statistic characteristics of “Underground Hot vortex” in China during 1980–1993 (I)

Using ground temperature data from meteorological stations as well as earthquake, ground tilt and precipitation data, the spatial-temporal distribution of “Underground Hot Vortex” (UHV) in China was analyzed in detail. The results show that concerning an “Underground Hot Vortex” cell, its life-span is 3–8 seasons, 1.5 years on average; the mean horizontal scale is 600 km and its characteristic velocity is about 400 km/a; UHV is likely to appear in some areas where the crustal movement is intense and the absolute value of vertical deformation rate is relatively high; its activity could hardly be detected in the area where the crust is stable and the vertical deformation is weak; most of “Underground Hot Vortex Groups” originate from the edge of Indian Plate, then migrate eastwards with a leaping-frog style. 5–10 years are needed for their arrival in the eastern border of China. Their horizontal migrating velocity is 200–500 km/a which is nearly equal to the characteristic velocity of a single UHV. Project sponsored by the National Climbing Project and Key Project of the Chinese Academy of Sciences.     

Flood and vortex scour of the channel bed of the Prosna river,and their depth range

Flood and vortex scour were observed in the Prosna channel (Central Poland) in the years 1980–1985. Flood scour increases the thickness of the reworked channel deposits by 30 per cent to 66 per cent, in relation to the thickness determined by the elevation of the normal bed and the bankfull stage. Vortex scour can increase the thickness by as much as 90–95 per cent. Knowledge of these properties of contemporary alluvium allows correct palaeohydrological and stratigraphic interpretation of the alluvial fills of valley floors.     

台风螺旋雨带——涡旋Rossby波

台风中的螺旋云雨带是由多种探测手段被观测到的现象 ,是为大家所共识的不争事实。但是 ,对它的形成、维持的理论解释 ,虽有多种学说 ,一直以来人们都倾向于重力惯性波说。而重力惯性波说有一个致命的弱点 ,即波的相速理论值为 10 1m/s量级 ,它要比螺旋云雨带实测移速只有 10 0 m/s几乎大一个量级。于是从前几年开始 ,人们又回到 30多年前提出的涡旋 Rossby波说那里去寻找合适的解释。经典的Rossby波是 β =(df/dy)作用的大尺度波动 ,而适用于台风中螺旋云雨带的涡旋———Rossby波乃是 f平面 (β =0 )上的中尺度波动。那末 ,对这两类尺度不同和成波机理不同的波动 ,何以均冠予Rossby波一词 ?本文试图从动力学等价原理上 ,对此作统一联系的说明。其结果是 :台风基本气流的涡度 ζ随径向 (r)变化的梯度d ζdr=1rr(r vλ) ,在动力学上等价于科氏参数 f随纬度变化的梯度即β=df/dy ;或者说它们在绝对涡度守恒的前提下 ,作为波扰动的成波机理是等价的     

The effect of shroud on vortex shedding mechanism of cylinder

In the present study, flow characteristics were investigated experimentally using particle image velocimetry technique (PIV) in a gap between a solid cylinder and a shroud to reveal the effect of shroud diameter (D_s) and porosity (β) on the vortex shedding mechanism of the cylinder. Porosity (varied from β = 0.3 to 0.7) and diameter ratio (D/D_s = 0.4, 0.5 and 0.6) were main parameters examined at a Reynolds number of Re = 5000. For the porosity values of β ≤ 0.5, it is observed that vortex formation of the cylinder occurs only in the gap and shroud produces its own wake flow patterns. Penetrating flow through the shroud extends the shear layers on the both sides of the shroud through the downstream direction and prevents the interaction of shear layers in the near wake region. The diameter ratio and the porosity are impactful on the wake flow patterns in outer region of the shroud since they are determinant of the penetrating flow rate. Force measurements were also performed in the air tunnel in order to reveal the effect of shroud on the drag coefficient of cylinder. It is found that the drag coefficient of the cylinders are reduced significantly by shrouds when compared with that obtained from the bare cylinder case. However, the drag coefficient of the cylinder together with the shroud is higher than the bare cylinder for all cases since the shrouds enlarge the area exposed to the flow.     

Piecewise uniform potential vorticity pancake shielded vortices

Shielded vortices consist of a core of potential vorticity (PV) of a given sign surrounded (or shielded) by a layer of opposite-signed PV. Such vortices have specific properties and have been the focus of numerous studies, first in two dimensional geometries (where PV is just the vertical component of the vorticity vector) and in geophysical applications (mostly in layered models). The present paper focuses on three-dimensional, spheroidal shielded vortices. In particular, we focus on vortical structures whose overall volume-integrated PV is zero. We restrict attention to vortices of piecewise uniform PV in the present research. We first revisit the problem within the quasi-geostrophic model, then we extend the results to the non-hydrostatic regime. We show that the stability of the structure depends on the ratio of PV between the inner core and the outer shield. In particular it depends on the polarity of the core and of the wavenumber of the azimuthal mode perturbed.