On the spiral structure of tropical cyclones

u nu m¶rt;a a u u¶rt;a ¶rt;a muna nua a n umu mnuu ua.

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Dedicated to Academician Alois Zátopek on His 65th Birthday     

On the merger of subsurface isolated vortices

Vortex merger is a phenomenon characterizing the whole class of geophysical vortices, from atmospheric storms and large oceanic eddies up to small scale turbulence. Here we focus on the merger of subsurface oceanic anticyclones in an idealized primitive equations model. This study has been motivated by past and recent observations of colliding lens-like anticyclones off of Gibraltar Strait. The critical conditions for merger (critical merger distance and time needed for merger) are determined. We will show that the predictions of classical two-dimensional merger are not verified for subsurface isolated vortices. For instance, critical merger distances will be reduced because of the vortex potential vorticity (PV) structure. The post-merger characteristics of the vortex (radius, extension and PV), are also determined. Merger-related effects, like production of peripheral filaments and small-scale eddies are also investigated and suggest the contribution of merger in both direct and inverse energy cascades.     

面向大气热力潮汐结构分析的Hough函数计算

作为一种刻画行星尺度大气波动基本结构的函数,Hough函数为开展有关大气潮汐全球结构的分析提供了具有物理基础的手段,它们也被作为一种数值工具应用于大气模式中以提高数值积分的效率.本文介绍了我们以拉普拉斯潮汐方程为基础,在发展求取Hough函数方面取得的进展,包括对有关计算方案和详细步骤的说明.针对39种分别具有三种主要频率,即周日、半日和1/3日,与此同时纬向波数落在[6,6]区间的潮汐成份,通过计算得到了与每一种成份对应的本征值、本征函数（Hough函数）集合.作为计算结果的示例,本文给出了针对迁移性周日潮和迁移性半日潮开展计算取得结果.这些结果说明这些函数具有正确的空间结构,与此同时还说明相关的本征值计算结果都达到了相当准确的水平.所有这些结果显示当前计算结果已经可以满足普通的应用.     

On the large-scale atmospheric turbulence

Summary The dynamical equations of the velocity correlation and spectrum functions for three-dimensional anisotropic turbulence in a stratified, rotating atmosphere are derived and discussed. The characteristics of the horizontal two-dimensional isotropic turbulence are analyzed.National Center for Atmospheric Research, sponsored by the National Science Foundation. On leave from the University of Utah, Salt LakeCity, Utah.     

On the existence of atmospheric attractors

In this paper, we consider the long-time dynamics for the primitive equations of large-scale dry at- mosphere. First, by energy methods, we obtain the existence and uniqueness of global strong solu- tions of the problem. Second, by studying the long-time behavior of strong solutions, we construct a global attractor which captures all the trajectories.     

On the cyclogenetic interaction between cyclone-scale vortices and cloud bands

Summary One type of cyclogenetic interaction between cloud bands and cloud vortices is described in terms of the linearized vorticity equation.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday     

On the nonlinear evolution of columnar vortices in a rotating environment

We examine the three-dimensional, nonlinear evolution of columnar vortices in a rotating environment. As the initial vorticity distribution, a wavetrain of finite amplitude Kelvin-Helmholtz vortices in shear is employed. Through direct numerical simulation of the Navier-Stokes equations we seek to better understand the process of maturation of the various three-dimensional modes of instability to which such vortical flows are subject, especially those which exist as a consequence of the action of the Coriolis force. In the absence of rotational influence, we thereby demonstrate that the nonlinear evolution of columnar vortices is most strongly controlled by one or the other of two mechanisms. One mechanism of instability is identifiable as a so-called elliptical instability, which promotes the initial bending of vortex tubes in a sinusoidal fashion, while the other is a hyperbolic mode, which is responsible for the development of streamwise vortex streaks in the "braids" between adjacent vortex cores. In the rotating case, anticyclonic vortices are strongly destabilized by weak background rotation, while rapid rotation stabilizes both the cyclones and anticyclones. The strong anticyclones are subject to two distinct forms of instability, namely a Coriolis force modified elliptical instability and an inertial (centrifugal) instability. The former instability is very similar to the nonrotating form of the elliptical instability as it promotes bending of vortex tubes, while the latter instability grows on the edge of the vortex core and generates streaks of vorticity, which surround the vortex core itself. These results of direct numerical simulation fully verify the results of previous linear stability analyses. Taken together, they provide a simple explanation for the broken symmetry that is often observed to be characteristic of the von Karman vortex streets that develop in the atmospheric lee of oceanic islands.     

On the atmospheric internal ship waves

The analytical solutions of the atmospheric internal ship waves induced by three-dimensional terrain are obtained by solving the atmospheric wave equation. The solutions show that the waves consist of the untrapped and trapped parts. The patterns of the diverging wave and transverse wave in the untrapped parts are mainly determined by the shape and orientation of the terrain. This kind of wave may transport the wave energy to the upper atmosphere. The patterns of trapped lee waves are decided by the atmospheric conditions such as stratification, mean wind speeds and wind shear.     

On the mean atmospheric circulation over Antarctica

Abstract

The south-easterly surface flow down the slopes of Antarctica induces a transfer of westerly angular momentum to the atmosphere, which must be removed from the Antarctic domain by atmospheric transports. It is suggested that synoptic eddies protruding from the northern baroclinic zone into the polar regions are modified by the topography such that they are able to perform these meridional transports. A simple linear two-layer model of the axisymmetric circulation of Antarctica is presented where the eddy effects are incorporated via a K-ansatz. It is shown that qualitatively realistic mean flow patterns can be obtained with this model. The limitations of this approach are exposed.     

On the seasonal variations of the atmospheric electric elements

Summary The air-earth current density in the stratosphere, the columnar resistance derived from the measurements of conductivity, and the ionospheric potential were investigated. The data were obtained by radiosonde ascents during the period of 1957–1967.It was found that the local horizontal visibility at the surface is related to the air-earth current density in the stratosphere, and it is expected that the air-earth current density has a seasonal variation. Statistical results show that indeed the air-earth current has a pronounced seasonal variation, high in winter and low in summer. The columnar resistance has also a seasonal variation, reverse to the variation of the air-earth current.The percentage time variation of the air-earth current (1/i) (di/dt) was found to be twice as much as the percentage time variation of the columnar resistance (1/R) (dR/dt) at the Tateno Observatory.The ionospheric potential, deduced from the measurements of the potential gradient by radiosonde ascents, shows no clear seasonal variation at Syowa-Base (Antarctica). Following Ohm's law, however, the above-mentioned results suggest that the seasonal variation of the ionospheric potential would exist on land.

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Zusammenfassung Die Vertikalstromdichte in der Stratosphäre, der Säulenwiderstand, berechnet aus Leitfähigkeitsmessungen, und das Ionosphärenpotential wurden untersucht. Die Messergebnisse wurden mittels Radiosonden im Jahrzehnt 1957–1967 erlangt.Es wurde festgestellt, dass die örtliche waagrechte Sichtweite am Erdboden mit der Vertikalstromdichte in der Stratosphäre korreliert ist, und dass erwartet werden muss, dass die Vertikalstromdichte einen jahreszeitlichen Gang aufweist. Tatsächlich lässt sich statistisch zeigen, dass ein solcher jahreszeitlicher Gang der Vertikalstromdichte besteht, mit einem Höchstwert im Winter und einem Mindestwert im Sommer. Auch der Säulenwiderstand zeigt einen jahreszeitlichen Gang, umgekehrt zu dem der Vertikalstromdichte.Die prozentuale zeitliche Änderung der Vertikalstromdichte (1/i) (di/dt) stellte sich als zweimal so gross heraus als die des Säulenwiderstandes (1/R) (dR/dt) gemessen am Observatorium zu Tateno.Wird das Ionosphärenpotential aus den Messungen des Potentialgefälles mit Radiosonden hergeleitet, so stellt sich bei den an der Syowa-Station in der Antarktik angestellten Messungen kein klarer Jahresgang heraus. Die hier zuvor erwähnten Ergebnisse, jedoch, führen zu der Annahme eines Jahresgangs des Ionosphärenpotentials über der genannten Station, wenn man das Ohm'sche Gesetz auf sie anwendet.

     

日面方位磁场扰动和行星际磁场螺旋结构

文采用球坐标下2.5维理想MHD模型,对日球子午面内方位磁场扰动的传播进行数值模拟,重点分析它对行星际磁场螺旋角的影响. 本文认为,观测到的行星际磁场螺旋角大于Parker模型的预言值,是太阳表面不断向行星际发出同向方位磁场扰动的结果;太阳较差自转在太阳内部产生的方位磁场为这类扰动提供了源头. 模拟结果表明,采用持续时间等于周期的十分之一、扰动幅度为103nT量级的正向方位磁场扰动,就可使1 AU处行星际磁场的螺旋角增加2°左右,与有关观测结果相符. 模拟结果还表明,上述方位磁场扰动对日球子午面内的太阳风特性和磁场位形的影响基本上可以忽略.     

Characteristics of the vertical structure of the atmospheric turbulence in the Tibetan Plateau

Science China Earth Sciences - The Tibetan Plateau (TP) has unique atmospheric dynamics and thermal structures that originate from its giant terrain and complex climate. High vertical-resolution...     

Effects of wind shear on the atmospheric convective boundary layer structure and evolution

The article reviews past accomplishments and recent advances in conceptual understanding, numerical simulation, and physical interpretation of the wind shear phenomena in the atmospheric convective boundary layer.     

On the structure of normal spiral galaxies with finite disk thickness part III: The asymptotic solution and the quantum condition of the general eigenvalue problem

Abstract

The asymptotic solution and the quantum condition of an eigen-value problem which appears in the density wave theory of the spiral galaxy are re-examined from a mathematical point of view. The dependence of the complex eigen-frequency ω on a large parameter λ is carefully discussed. It turns out that, in the expansion ω=∑^χ _i=o ωj/λj, the first term ωo must be real in order that the radiation condition may be satisfied. A related conclusion is that the quantum condition may be expressed in terms of an integral along the real axis of the complex plane of the independent variable. This form for the complex quantum condition is convenient not only for determining the complex eigen-frequency numerically, but also for drawing some physically interesting conclusions directly.     

On the ratio noise-signal of long-periodic oscillations in the general atmospheric circulation

Summary Characteristic features of long-periodic oscillations in the general atmospheric circulation may be deduced from the correlation existing between the monthly, the three-monthly, the six-monthly and the twelve-monthly figures of the barometric pressure at two distant stations and from the autocorrelation of the same figures at each station.It is shown that the monthly figures of the barometric pressure at Easter Island and those at Djakarta during the six years 1950–1955 have, when plotted as a function of time, one oscillation in common, whereas further these figures have both their own rhythms and their own noise. The period of the common oscillation is 28.6 months, while the phase difference between both stations amounts to 180°. The r.m.s. value of the noise is 0.76 times the value of the amplitude of the oscillation. The rhythms differ in wave length, amplitude and phase.It is also shown that the monthly figures of the barometric pressure at Ponta Delgada and those at Stykkisholm have, when plotted as a function of time, a whole spectrum of oscillations jointly, while all oscillations have the same phase difference (238°) between both stations. These features are deduced from observations during 40 years (1896–1915 and 1921–1940). If yearly figures are used instead of monthly ones, then the greater part of the spectrum of oscillations is smoothed away and only a few common oscillations are left. The first common oscillation has a wave length of 26.5 months and the second one has a wave length of 38.7 months.     

On the production of traveling ionospheric disturbances by atmospheric gravity waves

This paper deals with how atmospheric gravity waves produce the traveling ionospheric disturbances (TIDs) that are observed by ionosondes. It is shown that, rather than directly producing variations of ionospheric height, a likely mechanism involves changes in ionization density by gradients in the horizontal atmospheric gravity wave air motion. These density changes can be observed as variations of the height of an ionospheric isodensity surface (the usual way of measuring TIDs). This mechanism involving enhancement/depletion of ionospheric density requires quite moderate atmospheric gravity wave air motion speeds, and works well at almost all latitudes.     

Plasma vortices in the ionosphere and atmosphere

Vortices observed in ionized clouds of thunderstorm fronts have the nature of plasma vortices. In this work, the need to account for the electrostatic instability of plasma in the origination, intensification, and decay of plasma vortices in the atmosphere is shown. Moisture condensation results in mass-energy transfer under the inhomogeneous spatial distribution of aerosols. If a phase volume of natural oscillations is transformed in the frequency-wave vector space in inhomogeneous plasma, the damping of plasma oscillations promotes an increase in the pressure gradients normal to the geomagnetic field. Excitation of the gradient instabilities is probable in atmospheric plasma formations.