Atmosphere thermal structure

So far we have considered only the effect of the atmospheric thermal structure on a single line. However, in the thermal infrared, molecular bands are dominantly responsible for the gaseous opacity, and it is useful to see how they affect the appearance of spectra. We illustrate this with the 667 cm band of carbon dioxide (CO2) and the temperature profile shown in Fig. 4.3.1. This profile qualitatively... 

Prior to the Voyager 1 encounter, Danielson eta/. (1973) and Caldwell (1977) had developed a simple model for Titan s atmospheric thermal structure and haze that fit the ground-based far infrared data available at that time. In this model, an isothermal 160 K atmosphere containing a haze with an emissivity proportional to wavenumber overlay a surface of 78 K. The observed 1304 cm V4-band of CH4 and the 821 cm V9-band of C2H6 were adequately reproduced, as was the continuum between 300 and 600 cm (see Fig. 6.4.1a). Based on the Voyager 1 occultation temperature profile, it was natural to assume that the surface in the Danielson-Caldwell model corresponded to opaque methane clouds near the tropopause, and... 

Flasar, F. M., Conrath, B. J., Gierasch, P. J., Pirraglia, J. A. (1987). Voyager infrared observations of Uranus atmosphere thermal structure and dynamics. Journal of... 

Smith, M. D., Pearl, J. C., Conrath, B. J., Christensen, P. R. (2001). Thermal Emission Spectrometer results Mars atmospheric thermal structure and aerosol distribution. 

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. 

Role of composition in atmospheric physical process. The composition of the atmosphere plays a distinct set of roles in controlling and affecting certain physical processes of the atmosphere, most notably the thermal structure. 

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... 

The resultant O3 layer is critically important to life on Earth as a shield against LTV radiation. It also is responsible for the thermal structure of the upper atmosphere and controls the lifetime of materials in the stratosphere. Many substances that are short-lived in the troposphere (e.g. aerosol particles) have lifetimes of a year or more in the stratosphere due to the near-zero removal by precipitation and the presence of the permanent thermal inversion and lack of vertical mixing that it causes. 

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. 

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... 

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. 

Braun, D Holzer, G., "Polymerization of Vinyl Chloride at Atmospheric Pressure - Structure and Thermal Stability of the Polymers", Abstracts - Third International Symposium on PVC, Case Western Reserve University, Cleveland, August 10-15 ( 1980). 

One important point should be emphasized here. This is the paucity of spacecraft data on the chemical composition and thermal structure of Venus lower atmosphere below —22 km altitude (von Zahn et al., 1983). About 80% of Venus atmospheric mass is below this altitude. Furthermore, altitudes of 0-12 km span the region where the atmosphere is interacting with the surface. However, with three exceptions we have no data on the chemical composition of Venus nearsurface atmosphere. First is the older measurements of CO2 and N2 from crude chemical experiments on the Venera 4-6 landers. Second, the water-vapor profile measured by the Pioneer Venus large probe neutral mass spectrometer. Third, the measurements of water-vapor and gaseous sulfur by spectrophotometer experiments on the Venera II-I4 landers. The gas chromatograph and mass spectrometer experiments on... 

Other books of interest include Lewis and Prinn (1984), which emphasizes the use of observational data for understanding the origin, evolution, and present-day chemistry of planetary atmospheres. Krasnopolsky (1986) focuses on chemistry of the atmospheres of Mars and Venus. He also reviews the atmospheric composition, thermal structure, and cloud measurements by the Soviet Venera and Vega missions. Chamberlain and Hunten (1987) is the classic... 

The region of the atmosphere that is in direct contact with the surface (on a timescale of 1 h or less) is commonly referred to as the boundary layer or mixed layer. Technically, the boundary layer refers to the region of the atmosphere that is dynamically influenced by the surface (through friction or convection driven by surface heating). Less formally, the boundary layer is used to represent the layer of high pollutant concentrations in source regions. The top of the boundary layer in urban areas is characterized by a sudden decrease in pollutant concentrations and usually by changes in other atmospheric features (water vapor content, thermal structure, and wind speeds). 

Sunlight is absorbed when it hits ozone. This occurs on a large scale a few tens of kilometres above the Earth s surface (depending on latitude). The energy input makes the ozone warm, and it warms the rest of the air at this level. This effect, and also the various effects of the radiative budget in the air, especially the upper air, and the albedo of the surface, give the Earth s atmosphere a very odd thermal structure (Lewis Prinn 1984) (Fig. 2). 

In the Cambrian period life began to develop very quickly. For this reason the oxygen concentration increased rather rapidly. Thus, in the late Silurian (420 millions years ago) the oxygen level was as high as 0.1 PAL (Fig. 3) which is termed the second critical level. With the increase of the oxygen concentration the quantity of ozone in the atmosphere increased, together with an increase in the altitude of maximum ozone production. This latter, in the late Silurian period reached 20 km level, which made the spread of life onto dry land possible. At the same time the thermal structure of the atmosphere was drastically changed, which resulted in the appearance of the stratosphere. It was shown previously that our atmosphere has an... 

From the foregoing parts of this book it is clear that solar radiation in the stratosphere is primarily attenuated by ozone (see Subsection 3.4.3) and at a lesser extent by the stratospheric sulfate aerosol layer (see Subsection 4.4.3). This means that any change in the stratospheric 03 burden or aerosol concentration involves modification of radiative transfer in this atmospheric domain. We should remember that the residence time of trace constituents above the tropopause is rather long because of the thermal structure and the absence of wet removal. Furthermore at these altitudes the density of the air is low as compared to that of lower layers. For this reason even an insignificant quantity of pollutants can produce relatively long and significant effects. 

Figure 3.1. Schematic representation of the thermal structure of the atmosphere with its different layers.

One of the most important atmospheric dynamical quantities is the zonal wind (wind speed in the longitudinal direction). Wind velocities are conventionally positive for eastward winds (also called westerlies) and negative for westward winds (easterlies). They are mostly derived from the observed thermal structure of the atmosphere, although local values can be provided by radiosonde and radar measurements. To date, very few attempts have been made to directly measure the atmospheric wind components from space. The High Resolution Doppler Imager (HRDI) on board the Upper Atmosphere Research Satellite (UARS) has provided information on horizontal winds in the mesosphere/lower thermosphere (50-115 km) and in the stratosphere (10-40 km) by observing the Doppler shifts in the emission lines of an O2 atmospheric... 

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