Atmospheric motion

We concentrate on the information obtained from infrared spectroscopy and radiometry, both directly and in conjunction with other data sets, such as those from visible imaging. To provide the necessary background for the subjects of this section, we first review the equations of fluid motion and the succession of approximations leading to a tractable set of equations that can be used to describe the motion of a planetary atmosphere. Eor most of the cases considered, geostrophic balance and the associated thermal wind equations play major diagnostic roles in the inference of atmospheric motions from remotely sensed temperatures. For this reason, the derivation of these relations will be discussed in some detail. Other 

Remotely sensed data suitable for studies of atmospheric dynamics now exist for a variety of atmospheres. Mars provides an example of a rapidly rotating, shallow atmosphere with strong radiative forcing. Jupiter, Saturn, Uranus, and Neptune are rapidly rotating planets with massive atmospheres. Finally, Venus and Titan are both examples of slowly rotating bodies with deep atmospheres. Each of these cases is considered. 

The equations required to describe the motions of a planetary atmosphere include Newton s second law, the mass continuity equation, the first law of thermodynamics, and an equation of state for the atmospheric gas. These relations are briefly reviewed from a general point of view. More detailed discussions of the governing equations and their applications can be found in texts on dynamical meteorology and geophysical fluid dynamics, such as Pedloskey (1979), Haltiner Williams (1980), Holton (1992), and Salby (1996). 

In an inertial or nonaccelerating reference frame, Newton s second law can be written 

Using Eqs. (9.2.2) and (9.2.3), and explicitly displaying the pressure gradient, gravitational, and frictional terms contributing to G, Eq. (9.2.1) becomes 

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Dynamic meteorological models, much like air pollution models, strive to describe the physics and thermodynamics of atmospheric motions as accurately as is feasible. Besides being used in conjunction with air quaHty models, they ate also used for weather forecasting. Like air quaHty models, dynamic meteorological models solve a set of partial differential equations (also called primitive equations). This set of equations, which ate fundamental to the fluid mechanics of the atmosphere, ate referred to as the Navier-Stokes equations, and describe the conservation of mass and momentum. They ate combined with equations describing energy conservation and thermodynamics in a moving fluid (72) ... 

In order to estimate the extent of ozone depletion caused by a given release of CFCs, computer models of the atmosphere are employed. These models incorporate information on atmospheric motions and on the rates of over a hundred chemical and photochemical reactions. The results of measurements of the various trace species in the atmosphere are then used to test the models. Because of the complexity of atmospheric transport, the calculations were carried out initially with one-dimensional models, averaging the motions and the concentrations of chemical species over latitude and longitude, leaving only their dependency on altitude and time. More recently, two-dimensional models have been developed, in which the averaging is over longitude only. 

The energy that powers terrestrial processes is derived primarily from the sun and from the Earth s internal heat production (mostly radioactive decay). Solar energy drives atmospheric motions, ocean circulation (tidal energy is minor), the hydrologic cycle, and photosynthesis. The Earth s internal heat drives convection that is largely manifested at the Earth s surface by the characteristic deformation and volcanism associated with plate tectonics, and by the hotspot volcanism associated with rising plumes of especially hot mantle material. 

The strategy for research in the stratosphere has been to develop computer simulations to predict trends in photochemistry and ozone change. Incorporated in these simulations are laboratory data on chemical kinetics and photolytic processes and a theoretical understanding of atmospheric motions. An important aspect of this approach is knowing if the computer models represent the conditions of the stratosphere accurately enough that their predictions are valid. These models are made credible by comparisons with stratospheric observations. 

The second stage realizes a two-step procedure that re-calculates the ozone concentration over the whole space S = (tp, A, z) (, A)e l 0atmospheric boundary layer (zH 70 km), whose consideration is important in estimating the state of the regional ozonosphere. These two steps correspond to the vertical and horizontal constituents of atmospheric motion. This division is made for convenience, so that the user of the expert system can choose a synoptic scenario. According to the available estimates (Karol, 2000 Kraabol et al., 2000 Meijer and Velthoven, 1997), the processes involved in vertical mixing prevail in the dynamics of ozone concentration. It is here that, due to uncertain estimates of Dz, there are serious errors in model calculations. Therefore the units CCAB, MFDO, and MPTO (see Table 4.9) provide the user with the principal possibility to choose various approximations of the vertical profile of the eddy diffusion coefficient (Dz). 

TH E CEASELESS WIND An Introduction to the Theory of Atmospheric Motion, John A. Dutton. Acclaimed text integrates disciplines of mathematics and physics for full understanding of dynamics of atmospheric motion. Over 400 problems. Index. 97 illustrations. 640pp. 6 x 9. 65096-0 Pa. 16.95... 

Fortunately most constituents in the troposphere fall into two classes reactive species with photochemical lifetimes ranging from minutes to a few hours whose photo-chemically determined number densities can adjust to atmospheric motions and much less reactive species with photochemical lifetimes ranging from months to years and with tropospheric number densities represented by a single mixing ratio. 

It is well known that n (I O) and nfO ) are highly variable, but their inclusion as variables in the model would require that the models of global atmospheric motion be coupled to photochemistry, and this is not yet possible. Therefore at this time, it is necessary to fix nf O) and n(Oj) profiles at representative values (see Tables III and IV) and to assume a constant mixing ratio for n(NO) + n(N02) that is representative of available measurements (see Section II.E.2). n(CH ) and... 

In the absence of atmospheric motion and removal by precipitation, Be and Pb would remain where they originated—the upper troposphere and stratosphere and the lowermost meter of the atmosphere over continents and islands, respectively. In the real atmosphere, Be is mixed downward and Pb is mixed upwards and both are removed by precipitation. They are distributed through the atmosphere by eddy mixing. The residence time of aerosols is short compared to... 

Dobbins, R. A. (1979). Atmospheric Motion and Air Pollution. Wiley, New York. 

Assuming the location of the source xs is known (Figures 2.3, 2.5, 2.10, 2.11, 2.12 and 2.13) calculations of the near field dispersion first depend on the effective source scale Lse (which determines where the matter is dispersed by atmospheric motion) in relation to the separation distance between the buildings d. A finite volume of source material is initiated at time ts. If ls < d, then the matter disperses as if from a small isolated source. Given the time variation of the source strength <2(xs, t) the average concentration at a point x and time t can be calculated as a time integral from the initiation of the source to the measurement time t ... 

On the basis of photochemical considerations discussed in the last section we would expect a very different ozone distribution. For this reason it can be concluded that the pattern given by Fig. 10 can be explained only by the effect of atmospheric motions. This explanation is supported, together with other evidence by the fact that the results of individual measurements are also very much influenced by the atmospheric circulation. 

The distribution patterns shown in Fig. 11 can briefly be explained as follows. Stratospheric ozone formed by photochemical processes is transported in poleward direction by atmospheric motions. This circulation is particularly strong in winter and spring months when stratospheric air moves downward over polar regions. At the same time the lower stratosphere over the tropics is characterized by a slow updraft (Brewer, 1949). Thus, stratospheric dynamics lead to the accumulation of ozone rich air in the lower polar stratosphere. It should be recalled here that at this altitude 03 is a conservative property of the air. During the late spring and summer, especially, the stratospheric 03 reaches the troposphere first of all through the tropopause gaps. In the troposphere this species is removed from the air by various sinks, as this will be shown in the next section. 

Airborne sea salt particles are transported to higher levels and over the continents by atmospheric motions. Because of the relationship between relative humidity and particle size (see Section 4.5), low relative humidity promotes the transport of sea salt particles. 

Statistical models, in which the variables depend only on geographical latitude and time. In these models large scale atmospheric motions are taken into account statistically. 

The distribution of most chemical species in the middle atmosphere results from the influences of both dynamical and chemical processes. In particular, when the rates of formation and destruction of a chemical compound are comparable to the rate at which it is affected by dynamical processes, then transport plays a major role in determining the constituent distribution. In an environment like the Earth s atmosphere, air motions, and hence transport of chemical species, are strongly constrained by density stratification (gravitational force) which resists vertical fluid displacements, and the Earth s rotation (Coriolis force) which is a barrier against meridional displacements. Geophysical fluid dynamics describes how atmospheric motions are produced within these constraints. 

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). 

As indicated earlier, atmospheric motions are often advantageously represented in an isentropic coordinate system. In this case, Ertel s potential vorticity is defined by... 

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