Three-dimensional turbulent structures at a medium-sized confluence with and without an ice cover

River confluences are characterized by a complex mixing zone with three-dimensional (3D) turbulent structures which have been described as both streamwise-oriented structures and Kelvin–Helmholtz (KH) vertical-oriented structures. The latter are visible where there is a turbidity difference between the two tributaries, whereas the former are usually derived from mean velocity measurements or numerical simulations. Few field studies recorded turbulent velocity fluctuations at high frequency to investigate these structures, particularly at medium-sized confluences where logistical constraints make it difficult to use devices such as acoustic doppler velocimeter (ADV). This study uses the ice cover present at the confluence of the Mitis and Neigette Rivers in Quebec (Canada) to obtain long-duration, fixed measurements along the mixing zone. The confluence is also characterized by a marked turbidity difference which allows to investigate the mixing zone dynamics from drone imagery during ice-free conditions. The aim of the study is to characterize and compare the flow structure in the mixing zone at a medium-sized (~40 m) river confluence with and without an ice cover. Detailed 3D turbulent velocity measurements were taken under the ice along the mixing plane with an ADV through eight holes at around 20 positions on the vertical. For ice-free conditions, drone imagery results indicate that large (KH) coherent structures are present, occupying up to 50% of the width of the parent channel. During winter, the ice cover affects velocity profiles by moving the highest velocities towards the centre of the profiles. Large turbulent structures are visible in both the streamwise and lateral velocity components. The strong correlation between these velocity components indicates that KH vortices are the dominating coherent structures in the mixing zone. A spatio-temporal conceptual model is presented to illustrate the main differences on the 3D flow structure at the river confluence with and without the ice cover. © 2019 John Wiley & Sons, Ltd.     

一类奇异孤波解及其在高原低涡结构分析中的应用

文中利用相平面分析法 ,由非绝热大气运动方程组导出了与非线性重力内波有关的 Kd V方程 ,然后用直接积分法得到两类有意义的孤立波解 ,重点分析了一类具有间断点的奇异孤立波解的特征 ,初步建立了此波解与一类青藏高原暖性低涡的联系 ,讨论了高原加热和层结稳定度对高原低涡生成和移动的影响 ,并且从理论上论证了高原低涡具有与热带气旋类低涡( Tropical cyclone- like vortices)类似的涡眼和暖心结构     

海洋中长生命反气旋涡在地形上的演变以及涡旋的合并现象

通过对海洋中长生命反气旋涡在Ｇａｕｓｓ型孤立地形上演变的研究,发现地形对长生命反气旋涡的发展和传播有相当重要的影响。在无地形作用的情况下,仅有反气旋涡能够存在于向西的均匀基流中,这个涡是长生命的,并且在西移过程中有明显的向西倾斜。然而当其上游存在一个孤立地形时,可以发现这个涡有一个向东的倾斜,它的强度将增强且向西的移速会增加,其规迹象陀螺的运动。另一方面,当两个强度相同的反气旋涡同时存在时,这两个     

双台风生消过程涡旋能量、水汽输送相互影响的三维物理图像

重点研究“莫拉克”台风发展并登陆台湾,以及“天鹅”台风消亡阶段两者相互作用的问题。通过诊断分析发现“莫拉克”与“天鹅”移动过程存在双台风涡旋互旋、吸引与合并现象。采用双台风中心连线的垂直剖面移动坐标分析法可揭示出双台风涡度、风场三维结构,演变过程中双台风的涡度、动能强度呈反向变化关系,在双台风生消过程中,动能、位涡场分布存在显著“连体”通道特征。并揭示出双台风涡旋各自生、消过程水汽、动能可能存在的相互影响及其涡旋结构变化的内在关联。对“天鹅”消亡、“莫拉克”引发暴雨过程,采用Flexpart-WRF耦合模式模拟“质点群”轨迹,模拟结果再现了双台风生消阶段“天鹅”台风水汽“粒子群”向“莫拉克”低层气旋式输入通道,且在“莫拉克”涡旋高层反气旋式卷出的三维立体动态图像。通过剔除“天鹅”台风涡旋数值模拟试验进一步印证了“天鹅”台风趋于消弱过程其水汽、动能输送为“莫拉克”台风发展与维持做出了一定贡献。基于以上合成分析、轨迹和数值模拟技术综合分析提出了能揭示“天鹅”消亡、“莫拉克”发展过程能量、水汽输送相互影响的三维物理图像。     

Cyclonic-anticyclonic asymmetry and a new soliton concept for rossby vortices in the laboratory,oceans and the atmospheres of giant planets

Abstract

It is demonstrated in laboratory experiments with rotating shallow water that large scale Rossby vortices, greater than the Rossby-Obukhov radius in size, have dispersive and non-linear properties that are fundamentally different for the two possible polarities. We call this “cyclonic-anticyclonic asymmetry”. This asymmetry manifests itself in the following way: first, anticylones, unlike cyclones, do not undergo the dispersive spreading inherent in a linear wave packet. and therefore, having a considerably longer natural lifetime, are obvious candidates for Rossby solitons; second, dipolar vortices are, because of the comparatively rapid decay of a cyclone, transformed into anticyclonic solitons; third, anticyclones are much more readily generated by zonal flows of the type existing in planetary atmospheres. The evident dominance of anticyclones amongst the long-lived vortices in the atmospheres of giant planets strongly suggests that the cyclonic-anticyclonic symmetry plays a decisive role in the atmospheric cyclogenesis of large planets.

According to our concept, the Rossby soliton is a “real” vortex; unlike a wave, it retains some fluid particles within it throughout its lifetime. Two similar solitons can merge by mutual collisions. This picture of a “vortical” soliton differs in an essential way from the earlier idea due to Maxworthy and Redekopp (1976) of purely “wave-like” Rossby solitons that can freely pass through one another.

Laboratory experiments were performed by us to simulate the new Rossby solition, with special reference to naturally-occurring vortices of the same general type as Jupiter's great red spot. The experimental data presented contradict the idea of “pure wave solitons” but confirm our concept of “vortical solutions”.     

Synoptic features and structures of some equatorial vortices over the South China Sea in the Malaysian region during the winter monsoon,December 1973

In December 1973, Peninsular Malaysia and Sarawak experienced a few periods of heavy rain caused by westward moving equatorial vortices from the South China Sea. In this report, the synoptic characteristies associated with the development and intersification of these vortices are shown. Structure of one of the disturbances was examined. Disturbances in the trades associated with lateral shear were found to be important for the genesis of the equatorial vortices. However, the intensification of these disturbances depended on the interaction with the cold monsoon surge.     

Point vortex dynamics for coupled surface/interior QG and propagating heton clusters in models for ocean convection

Abstract

The dynamic behavior of baroclinic point vortices in two-layer quasi-geostrophic flow provides a compact model for studying the transport of heat in a variety of geophysical flows including recent heton models for open ocean convection as a response to spatially localized intense surface cooling. In such heton models, the exchange of heat with the region external to the compact cooling region reaches a statistical equilibrium through the propagation of tilted heton clusters. Such tilted heton clusters are aggregates of cyclonic vortices in the upper layer and anti-cyclonic vortices in the lower layer which collectively propagate almost as an elementary tilted heton pair even though the individual vortices undergo shifts in their relative locations. One main result in this paper is a mathematical theorem demonstrating the existence of large families of long-lived propagating heton clusters for the two-layer model in a fashion compatible to a remarkable degree with the earlier numerical simulations. Two-layer quasi-geostrophic flow is an idealization of coupled surface/interior quasi-geostrophic flow. The second family of results in this paper involves the systematic development of Hamiltonian point vortex dynamics for coupled surface/interior QG with an emphasis on propagating solutions that transport heat. These are novel vortex systems of mixed species where surface heat particles interact with quasi-geostrophic point vortices. The variety of elementary two-vortex exact solutions that transport heat include two surface heat particles of opposite strength, tilted pairs of a surface heat particle coupled to an interior vortex of opposite strength and two interior tilted vortices of opposite strength at different depths. The propagation speeds of the tilted elementary hetons in the coupled surface/interior QG model are compared and contrasted with those in the simpler two-layer heton models. Finally, mathematical theorems are presented for the existence of large families of propagating long-lived tilted heton clusters for point vortex solutions in coupled surface/interior QG flow.     

Large Eddy Simulation of typical dust devil-like vortices in highly convective Martian boundary layers at the Phoenix lander site

Physical characteristics of naturally formed convective vortices in the Phoenix Mars lander environment have been investigated on a relatively hot summer Martian arctic day. For this, the NCAR LES has been adapted and developed to conduct three micro-scale simulations of the Martian Convective Boundary Layer (CBL), in situations with and without geostrophic wind, and atmospheric radiative flux divergence. Time series analysis of the vortices’ properties is discussed. The study confirms the decrease of vortex populations in windy conditions and also illustrates that intense but small vortices are expected to be observed in higher geostrophic wind situations. This may lead to more dust migration rather than dust devil formation on windy days. The background (geostrophic) wind causes the vortices to become less cyclostrophically balanced.     

Squall Line and Its Vertical Motion Under Different Moisture Profiles in Eastern China

The impacts of different moisture profiles on the structure and vertical motion of squall lines were investigated by conducting a set of numerical simulations. The base state was determined by an observational sounding, with high precipitable water representing moist environmental conditions in the East Asian monsoon region. To reveal the impact of moisture at different levels, the moisture content at the middle and low levels were changed in the numerical simulations. The numerical results showed that more convective cells developed and covered a larger area in the high moisture experiments, which was characteristic of the convection during the Meiyu season in China. In addition, high moisture content at low levels favored the development of updrafts and triggered convection of greater intensity. This was demonstrated by the thermodynamic parameters, including Convective Available Potential Energy (CAPE), Lifted Index (LI), Lift Condensation Level (LCL), and Level of Free Convection (LFC). Dry air at middle levels led to strong downdrafts in the environment and updrafts in clouds. This could be because dry air at middle levels favors the release of latent heat, thereby promoting updrafts in clouds and downdrafts in the environment. Therefore, high relative humidity (RH) at low levels and low RH at middle levels favors updrafts in the cloud cores. Additionally, moist air at low levels and dry air at middle levels promotes the development of convective cells and the intensification of cold pool. The squall line can be organized by the outflow boundary induced by cold pool. The balance of cold pool and environmental wind shear is favorable for the maintenance and strengthening of squall lines.