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Atmosphere Basics: Layers, Pressure, Temperature, and Moisture

The atmosphere is the protective layer of gases surrounding Earth, essential for life and weather. It holds the air we breathe, shields us from space, and contains moisture, gases, and tiny particles. This layer is composed mainly of nitrogen, oxygen, argon, and carbon dioxide, with water vapor varying up to about 4%. The atmosphere is divided into layers based on temperature and pressure changes, each with unique characteristics. Understanding these layers, how pressure and temperature vary with altitude, and the role of moisture is crucial for grasping weather patterns and atmospheric behavior. This knowledge helps explain phenomena like cloud formation, precipitation, and the dynamics of weather systems.

Figures (7)

Figure 10.30 The physical state of a substance and its phase-transition temperatures are represented graphically in a phase diagram.
Figure 10.31 The pressure and temperature axes on this phase diagram of water are not drawn to constant scale in order to illustrate several important properties.
Figure 10.32 Freeze-dried foods, like this ice cream, are dehydrated by sublimation at pressures below the triple point for water. (credit: ʺlwaoʺ/Flickr)
Figure 10.33 The immense pressures beneath glaciers result in partial melting to produce a layer of water that provides lubrication to assist glacial movement. This satellite photograph shows the advancing edge of the Perito Moreno glacier in Argentina. (credit: NASA)
Figure 10.34 A phase diagram for carbon dioxide is shown. The pressure axis is plotted on a logarithmic scale to accommodate the large range of values.
Figure 10.35 (a) A sealed container of liquid carbon dioxide slightly below its critical point is heated, resulting in (b) the formation of the supercritical fluid phase. Cooling the supercritical fluid lowers its temperature and pressure below the critical point, resulting in the reestablishment of separate liquid and gaseous phases (c and d). Colored floats illustrate differences in density between the liquid, gaseous, and supercritical fluid states. (credit: modification of work by “mrmrobin”/YouTube)
Figure 10.36 (a) Caffeine molecules have both polar and nonpolar regions, making it soluble in solvents of varying polarities. (b) The schematic shows a typical decaffeination process involving supercritical carbon dioxide.

From the ground up, the troposphere is where all weather happens. It gets colder as you go higher, and its height varies from about 4 miles at the poles to 12 miles at the equator. Above it is the stratosphere, where temperature increases with height due to ozone absorbing sunlight.

The mesosphere and thermosphere follow, with the thermosphere getting very hot from solar radiation, though it feels cold due to sparse air. The exosphere is the outermost layer, where gases escape into space. Pressure drops as you go up, measured in hectopascals (hPa), with sea level at about 1013 hPa.

It varies from nearly zero in deserts to up to 4% in tropical areas. Water cycles through evaporation, transpiration, condensation, and precipitation, forming clouds and rain.

Key Points

  • The troposphere is the lower atmosphere where almost all weather occurs, extending from the Earth's surface up to about 11-12 miles (18-20 km) at the equator, with its height decreasing toward the poles.
  • The mesosphere is the layer of the atmosphere extending from around 31 miles (50 km) to 53 miles (85 km) above the Earth's surface, where temperatures increase as one descends due to the thickening gases.
  • The thermosphere is the upper atmosphere layer extending from about 53 miles (85 km) to 375 miles (600 km) above the Earth, where temperatures increase with height due to the absorption of high-energy radiation from the sun.
  • Atmospheric pressure is the force exerted by the weight of the air above a given point, measured in units such as pascals, millibars, or hectopascals, and it decreases with increasing altitude.
  • Standard atmospheric pressure is the average pressure at sea level, defined as 1013.25 millibars or hectopascals, which is the commonly accepted reference for measuring air pressure.

Terms

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