Structure of the atmosphere

The Structure of the atmosphere of the Earth in Fig. 2.20 is defined in terms of the variations of pressure and temperature that occur with increasing altitude above the surface of the Earth. The major structural units are  

In all atmospheric layers the density and the pressure of the air decrease with increasing altitude. Under normal conditions near the Earth s surface when the temperature and pressure are 0 °C and 1013.25 mb, respectively, the air density is equal to 1.2923 x 10 3 g/cm3.1 Around 100 km the density is about 106 times smaller. 

According to the character of the thermal structure, the homosphere is divided into three further layers. The lowest one is termed the troposphere. The altitude of the troposphere is approximately 18 km above the equator and 8 km above the poles. In this layer the temperature generally decreases with increasing altitude2 (Fig. 1). The average temperature gradient is equal to 6.5 °C/km. 

The troposphere receives the thermal energy from the Earth s surface which absorbs the Sun s radiation. Because of the heating of the air by the infrared radiation emitted by the surface, intensive vertical (convective) motions can be generated. This convection transports heat, water vapour and other trace constituents of surface origin to the higher levels of the troposphere. In such an 

2 On occasion there are thin lavers in the troposphere in which the temperature is constant or increases with height. These are called isothermal and inversion layers, respectively. 

The structure of the atmosphere according to Nicolet (1964). The plotted curve gives the temperature profile, whi le AY, and g are t he molecular weight and the gravitational constant, respectively. (By courtesy 

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The averaging time of the rapid-response record [Fig. 4-1 (a)] is an inherent characteristic of the instrument and the data acquisition system. It can become almost an instantaneous record of concentration at the receptor. However, in most cases this is not desirable, because such an instantaneous record cannot be put to any practical air pollution control use. What such a record reveals is something of the turbulent structure of the atmosphere, and thus it has some utility in meteorological research. In communications... 

The values of Gy and Gz vary with tlie turbulent structure of the atmosphere, tlie height above the surface, tlie surface rougluiess, the sampling time over wliich tlie concentration is to be estimated, tlie wind speed, and tlie distance from tlie source. For tlie parameter values tliat follow, the sampling time was originally assumed to be about 10 minutes, tlie height to be tlie lowest several hmidred meters of tlie atmosphere, and tlie surface to be relatively open country. The parameters are estimated from tlie stability of the atmosphere. 

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. 

Another major feature of the vertical thermal structure of the atmosphere is due to the presence of ozone, O3, in the stratosphere. This layer is caused by photochemical reactions involving oxygen. The absorption of solar UV radiation by O3 causes the temperature in the stratosphere and mesosphere to be much higher than expected from an extension of the... 

Since feedbacks may have a large potential for control of albedo and therefore temperature, it seems necessary to highlight them as targets for study and research. Besides the simple example above of cloud area or cloud extent, there are others that can be identified. High-altitude ice clouds, for example, (cirrus) have both an albedo effect and a greenhouse effect. Their occurrence is very sensitive to the amount of water vapor in the upper troposphere and to the thermal structure of the atmosphere. There may also be missing feedbacks. 

Much of the electromagnetic spectrum has been used to investigate the structure of matter in the laboratory but the atmospheric windows restrict astronomical observations from Earth. Irritating as this is for astronomers on the ground, the chemical structure of the atmosphere and the radiation that it traps is important to the origins of life on Earth. The light that does get through the atmosphere, however, when analysed with all of the tools of spectroscopy, tells the molecular story of chemistry in distant places around the Universe. 

This chapter reviews and clarifies some of the main features in the pattern and rate of transport of nuclear bomb debris from the upper atmosphere down to the surface of the earth. The atmospheric nonmen-clature used is that based on the thermal structure of the atmosphere and recommended by the International Union of Geodesy and Geophysics at Helsinki in 1960, shown in Figure 1. Starting with the lower thermosphere, the important mechanisms of vertical transport are discussed... 

Ozone is an important gas in the atmosphere since, although it is only present in tiny quantities, it plays a vital role in protecting mankind from the harmful effects of solar radiation and a dominant part in determining the temperature structure of the atmosphere. 

The emission of C02 from anthropogenic activities (the combustion of C-based fossil fuels, deforestation, combustion of woods) amounts to approximately 7.5 Gtc per year, or about 3.5% of the total amount cycled in the natural cycle. However, as the natural systems are unable to use such C02, this leads to its accumulation into the atmosphere. The assumption that an increase of the concentration of C02 in the atmosphere would have boosted both the photosynthesis and the dissolution into the oceans has not been proven to be true. In fact, the solubility of C02 is governed by complex equilibria, while photosynthetic fixation is limited by several factors so that, under the increase of the atmospheric concentration from 280 ppm of the preindustrial era to the present-day 380 ppm, there has not been any sensible improvement of the uptake. Therefore, under natural conditions the uptake of C02 has reached an equilibrium state, and the further increase in atmospheric concentrations may more likely cause climate changes through the greenhouse effect and destabilization of the thermal structure of the atmosphere, than improve the elimination of C02 from the atmosphere. 

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... 

WATOX-82, -83, and -84 sampled air in the marine boundary layer. These sea-level measurements gave no information about upper-air transport. To overcome this deficiency, the fourth through the seventh Intensives incorporated data collected onboard two NOAA research aircraft, the NOAA WP-3D and the NOAA KingAir. (See Table III for the specific species measured.) Both aircraft carried sampling and analytical equipment designed to determine the vertical and horizontal chemical structure of the atmosphere. 

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

Eddy Diffusion Coefficients. The eddy diffusivities, Kh (x,y,z,t) and Kv (x,y,z,t), which depend on the turbulent structure of the atmosphere, are two of the more elusive quantities that must be estimated. They are not established through direct measurement they must be calculated from observed data. Most of the data that have been acquired to determine Kr (or Kh) have been limited to the surface layer (79) few data are available for conditions under which an elevated inversion was present. As a result, relatively little guidance is available in the literature that can be used to estimate these parameters. 

Eschenroeder and Martinez (21) reviewed the literature pertaining to the turbulent structure of the atmosphere and, based on this effort, proposed a trapezoidal profile for Ky. As an example, they report the following formulations for Ky for a 180 meter inversion base 30 square meters/min at the ground, increasing linearly to a height of 80 meters, at which height Ky = 50(u 5) square meters/min (u is the horizontal... 

FIGURE 20.28 The variation of the temperature of the atmosphere with altitude, showing the layered structure of the atmosphere. 

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.). 

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