Atmosphere vertical structure

Fig. 7-1 Atmospheric vertical structure including temperature composiHon and conventional names of atmospheric layers or altitude regions.

In incompressible fluids, such as water, the vertical structure of temperature very simply reveals the stability of the fluid. When the lower layer is warmer and thus less dense than the upper layer, the fluid is unstable and convective currents will cause it to overturn. When the lower layer is cooler than the upper layer, the fluid is stable and vertical exchange is minimal. However, because air is compressible, the determination of stability is somewhat more complicated. The temperature and density of the atmosphere normally decrease with elevation density is also affected by moisture in the air. 

Altitude dependence. The composition varies with altitude. Part of that vertical structure is due to the physical behavior of the atmosphere while part is due to the influence of trace substances (notably ozone and condensed water) on thermal structure and mixing. 

Before setting out to discuss the vertical structure of the atmosphere, we note that it is useful to have access to conventional nomenclature. Figure 7-1, based on the thermal profile of the atmosphere, includes a number of commonly used definitions. 

The turnover time of water vapor in the atmosphere obviously is a function of latitude and altitude. In the equatorial regions, its turnover time in the atmosphere is a few days, while water in the stratosphere has a turnover time of one year or more. Table 7-1 Qunge, 1963) provides an estimate of the average residence time for water vapor for various latitude ranges in the troposphere. Given this simple picture of vertical structure, motion, transport, and diffusion, we can proceed to examine the behavior of... 

The advection scheme of the regional model is improved to take into account the surface orography. Terrain following vertical structure of the model domain with higher resolution was incorporated. Wet removal of heavy metals from the atmosphere was enhanced by developing newparameterizations of precipitation scavenging. Both in-cloud and sub-cloud wet removal were modified on the basis of the up-to-date scientific literature data. 

Yee, E., R. Chan, P. R. Kosteniuk, G. M. Chandler, C. A. Biltoft, and J. F. Bowers. The vertical structure of concentration fluctuation statistics in plumes dispersion in the atmospheric surface layer. Bound.-Lay. Meteorol. 76, 41-67 (1995). 

One of the reasons for these differences could be the fact that the semi-empirical model SDS was based on data only from the 700 gPa surface level, whereas the two other models took into account the vertical structure of the atmosphere. However, this comparison does not allow us to draw a conclusion about which of the obtained results correctly reflect the effect of forcing. To answer this question and to determine the reasons for the above-mentioned differences, numerical modeling needs to be further improved. 

As part of ITOP, measurements were carried out onboard the flying laboratory Falcon-20 which was able to monitor aerosol concentration and gas traces north of Paris in July-August 2004. Synchronous measurements were made with ground-based aerosol lidar which made it possible to assess the vertical structure of the atmosphere. During these measurements aerosols were detected from Canada and Alaska having crossed the North Atlantic, where at this time there was biomass burning. The Falcon-20 s equipment enabled us to... 

De Rosnay et al. (2000) assessed the reliability of schemes that parameterize land surface processes to find the correspondence between calculated mean annual fluxes of energy and moisture depending on detailed consideration of the vertical structure of soil. These schemes are used in general circulation models of the atmosphere (GCMAs). The calculations testify to the strong dependence of fluxes on vertical resolution. The 11-layer scheme parameterizing heat and moisture transfer in the top 1 mm thick layer of soil was found to be adequate. 

Dimethvlsulfide. The literature data base concerning the atmospheric concentration of DMS in the marine atmosphere can be divided into two subsets, 1) shipboard studies and 2) aircraft studies. The former yield information concerning the variability within the marine boundary layer, while the latter yield information concerning the vertical structure and mixing processes affecting the DMS concentrations. The boundary layer data are summarized in Table I. 

Figure 1 Vertical structure of the atmosphere. The vertical profile of temperature can be used to define the different atmospheric layers...

FIGURE 4-1 Vertical structure of the atmosphere. Weather phenomena are confined almost entirely to the troposphere, as are most air pollutants, which are removed by various processes before they can mix into the stratosphere. Certain long-lived pollutants, however, such as the chlorofluorocarbons (CFCs), do mix into the stratosphere, and other pollutants can be injected physically to stratospheric altitudes by processes such as volcanic eruptions or nuclear explosions. Note that more than one term may refer to a given layer of the atmosphere (adapted from Introduction to Meteorology, by F. W. Cole. Copyright 1970, John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.). 

Fig. 3.2 The vertical structure of the atmosphere and associated temperature and pressure variation. Note the logarithmic scale for pressure. The inset shows gas concentration as a function of height in the heterosphere and illustrates the presence of lighter gases (hydrogen and helium) at greater heights.

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). 

Relation (3.13) can be used to characterize the vertical structure of the atmosphere in a convenient form. For example, the vertical distributions of the pressure and air density can be represented by, respectively... 

The vertical structure of the ocean features a decrease of temperature with increasing depth and a correspondingly stable stratification. A shallow surface layer of 50-100 m thickness is vertically well mixed due to agitation by wind force. This portion represents only a small subvolume, but it is of crucial importance to the exchange of C02 with the atmosphere. Compared with the bulk of the ocean, the mixed layer responds quickly to changes in the atmosphere and it must be treated as a separate reservoir. The depth of the mixed layer is variable. We adopt the recommendation of Bolin et al. (1981) and use a value of 75 m. This is a seasonal average obtained by Bathen (1972) from measurements in the Pacific Ocean. 

Along the coast of California during north-westerly up-welling favorable winds, the marine atmospheric boundary layer is characterized by a low-level jet, with peak wind speeds of as much as 30 m/sec at elevations of a few hundred meters. The vertical structure is marked by an inversion, usually at or near the elevation of the wind speed maximum. Above the inversion, the stratification is stable, and the wind shear is caused primarily by baro-clinicity (thermal wind) generated by the horizontal temperature gradient between the ocean and land. Below the inversion, the flow is turbulent. 

In representing the vertical structure of the continuously stratified atmosphere it is generally necessary to discretize the vertical dependence so that the semiinfinite atmosphere may be approximated by a finite number of parameters. Often finite differences at a prespecified number of levels are used to represent the vertical structure. Another method is to divide the atmosphere into a finite number of homogeneous layers, as shown in Fig. 2. This representation is often used in dynamic oceanography, which has many similarities to dynamic meteorology, essentially because the Rossby number is also small for large-scale motions in the ocean. Both disciplines may be considered subsets of geophysical fluid dynamics. 

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. 

Fig. 5.4 Vertical structure of the atmosphere at a glance a layers of air, and temperature, b chemical mixing, c radio wave reflection levels. Values given are very approximate, and depend on location and season...

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