Atmospheric Waves

Waves are key dynamical features of the atmosphere. They can be defined as propagating disturbances of material contours whose 

Waves are characterized by their amplitudes and their phases, as well as by their phase speeds (which describe the rates at which the crest and the trough of the waves propagate) and their group speeds (which are a measure of the rate at which the energy of the disturbance propagates). 

Gravity waves are oscillations with relatively short horizontal wavelengths (typically 10-1000 km) that arise in a stably stratified fluid when air parcels are being displaced vertically. These waves are produced by air flow over mountains (orographic waves) or by other (not well identified) non-orographic sources such as thunderstorms, frontal 

In the equatorial upper stratosphere and lower mesosphere, low zonal wavenumber pancake structures have frequently been observed (Hitchman et al, 1987), and are suggestive of inertially unstable motions. The sources and dynamics of such disturbances need to be elucidated. 

Finally, the tides observed in the mesosphere and thermosphere should be mentioned. Atmospheric solar tides are global-scale waves with periods that are harmonics of a 24-hour day. These oscillations are 

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Carslaw, K. S., M. Wirth, A. Tsias, B. P. Luo, A. Dombrack, M. Leutbecher, H. Volkert, W. Renger, J. T. Bacmeister, E. Reimers, and Th. Peter, Increased Stratospheric Ozone Depletion Due to Mountain-Induced Atmospheric Waves, Nature, 391, 675-678 (1998a). 

The sections of this chapter deal with the following elements of atmospheric dynamics vertical structure of the atmosphere (Section 3.2), fundamental equations of atmospheric motions (Section 3.3), transport of chemical constituents and the relative importance of dynamical and chemical effects on photochemical species (Section 3.4), atmospheric waves (Section 3.5), the mean meridional circulation and the use of the transformed Eulerian formalism to illustrate the roles of mean meridional and eddy transports (Section 3.6), the important role of wave transience and dissipation (Section 3.7), vertical transport by molecular diffusion in the thermosphere (Section 3.8), and finally, models of the middle atmosphere (Section 3.9). 

It should be emphasized that Figure 3.5 presents the mean zonal wind, that is, the wind speed averaged over longitude and time. In addition, local variations in the wind speed and direction are observed. These dynamical disturbances are associated with the presence of atmospheric waves (see Section 3.4). The propagation of these waves through the atmospheric medium is determined by the basic state of the atmospheric fluid at the same time, the dissipation of the waves tends to modify the basic state itself. Beside radiatively forced seasonal variations,... 

The more complex dynamics of the Arctic vortex as compared to the Antarctic demand the application of sophisticated tools for analysis of ozone destruction. The greater wave activity of the Northern Hemisphere can enhance ozone losses even in winter by increasing the exposure of polar air to sunlight in the distortions caused by atmospheric waves as compared to the Southern Hemisphere (see e.g., Jones et al, 1990a). However, the same wave activity can warm the air and perhaps... 

Aerosols Atmospheric Diffusion Modeling Atmospheric Turbulence Flow Visualization Image Restoration, Maximum Entropy Method Imaging Optics Mesoscale Atmospheric Modeling Radiation, Atmospheric Wave Phenomena... 

Eliassen-Palm flux A measure of the pseudomomentum associated with vertically propagating atmospheric waves. Its divergence gives the acceleration of the zonal-mean zonal wind by atmospheric waves. 

THE STRATOSPHERE is the layer of the Earth s atmosphere immediately above the troposphere it extends from a lower boundary (the tropopause) whose altitude varies between about 8 and 16 km to an upper boimdary (the stratopause) near 50 km. The stratosphere is characterized by increasing temperature with altitude, which is due primarily to the absorption of solar ultraviolet radiation by ozone. The meteorology of the stratosphere is governed mainly by the seasonal variation of heating due to absorption of solar radiation, and by the upward propagation of atmospheric waves originating in the troposphere. 

The disturbances in the stratospheric circulation seen in Fig. 7b are caused by atmospheric waves that propagate upward from the troposphere. The dominant type of wave in the extratropical stratosphere is the Rossby wave (see Section IV.B.2). Rossby waves found in the stratosphere are of very large scale, having horizontal wavelengths of tens of thousands of kilometers for these reason, these Rossby waves are often referred to as planetary waves. ... 

Under quasi-steady-state conditions, the existence of a mean meridional circulation outside of the tropics depends on the transport of momentum by atmospheric waves. Away from the equator / is much larger than so the lat-... 

In the preceding sections we have seen that wave dissipation, expressed by the EP flux divergence V F, plays a central role in determining the stratospheric circulation. We now present a brief description of the principal types of wave found in the stratosphere. Atmospheric waves can... 

A full description of atmospheric waves is beyond the scope of this work however, it is possible to gain some insights into the mechanisms responsible for wave motion by considering a simplified set of equations that govern the motions of the eddies, or perturbations, to the zonal-mean flow. This set consists of the momentum equations in the zonal and meridional directions. 

The relevance of these shallow-water equations for atmospheric motions is seen when the governing equations for the stratifled atmosphere are hnearized about an assumed basic state. If the basic-state wind field is assumed independent of height, the perturbation equations can generally be separated into an ordinary differential equation for the vertical structure of the variables, and a set of partial differential equations for the horizontal structure. The separation constant that appears in both sets is called the equivalent depth and is usually denoted by h. The equivalent depth is so-named because the horizontal structure equations appear very similar to the linearized equations for a shallow water fluid with mean fluid depth h equal to / e. The horizontal stracture of atmospheric waves is essentially identical to the solutions of the shallow-water equations. 

The occurrence of strong small-scale atmospheric disturbance (a pressure jump or a train of internal atmospheric waves). 

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