The Layering Of The Atmosphere

The atmosphere can be divided conveniently into a number of rather well-marked horizontal layers, mainly on the basis of temperature (Figure 2.15). The evidence for this structure comes from regular rawinsonde (radar wind-sounding) balloons, radio wave investigations, and, more recently, from rocket flights and satellite sounding systems. There are three relatively warm layers (near the surface; between 50 and 60 km; and above about 120 km) separated by two relatively cold layers (between 10 and 30 km; and 80 and 100 km). Mean January and July temperature sections illustrate the considerable latitudinal variations and seasonal trends that complicate the scheme (see Figure 2.16).

1 Troposphere

The lowest layer of the atmosphere is called the troposphere. It is the zone where weather phenomena and atmospheric turbulence are most marked, and it contains 75 per cent of the total molecular or gaseous mass of the atmosphere and virtually all the water vapour and aerosols. Throughout this layer, there is a general decrease of temperature with height at a mean rate of about 6.5°C/km. The decrease occurs because air is compressible and its density decreases with height, allowing rising air to expand and thereby cool. In addition, turbulent heat transfer from the surface mainly heats the atmosphere, not direct absorption of radiation. The troposphere is capped in most places by

Polar Stratospheric Cloud Mean

Figure 2.15 The generalized vertical distribution of temperature and pressure up to about 110 km. Note particularly the tropopause and the zone of maximum ozone concentration with the warm layer above. The typical altitudes of polar stratospheric and noctilucent clouds are indicated.

Source: After NASA (n.d.). Courtesy of NASA.

Figure 2.15 The generalized vertical distribution of temperature and pressure up to about 110 km. Note particularly the tropopause and the zone of maximum ozone concentration with the warm layer above. The typical altitudes of polar stratospheric and noctilucent clouds are indicated.

Source: After NASA (n.d.). Courtesy of NASA.

a temperature inversion level (i.e. a layer of relatively warm air above a colder layer) and in others by a zone that is isothermal with height. The troposphere thus remains to a large extent self-contained, because the inversion acts as a 'lid' that effectively limits convection (see Chapter 4E). This inversion level or weather ceiling is called the tropopau.se (see Note 5 and Box 2.2). Its height is not constant in either space or time. It seems that the height of the tropopause at any point is correlated with sea-level temperature and pressure, which are in turn related to the factors of latitude, season and daily changes in surface pressure. There are marked variations in the altitude of the tropopause with latitude (Figure 2.16), from about 16 km at the equator, where there is strong heating and vertical convective turbulence, to only 8 km at the poles.

The equator-pole (meridional) temperature gradients in the troposphere in summer and winter are roughly parallel, as are the tropopauses (see Figure 2.16), and the strong lower mid-latitude temperature gradient in the troposphere is reflected in the tropopause breaks (see also Figure 7.8). In these zones, important interchange can occur between the troposphere and stratosphere, and vice versa. Traces of water vapour can penetrate into the stratosphere by this means, while dry, ozone-rich stratospheric air may be brought down into the mid-latitude troposphere. Thus above-average concentrations of ozone are observed in the rear of mid-latitude low-pressure systems where the tropopause elevation tends to be low. Both facts are probably the result of stratospheric subsidence, which warms the lower stratosphere and causes downward transfer of the ozone.

Stream Isolines

Figure 2.16 Mean zonal (westerly) winds (solid isolines, in knots; negative values from the east) and temperatures (in °C, dashed isolines), showing the broken tropopause near the mean Ferrel jet stream.

Source: After Boville (from Hare 1962). Notes: The term 'Ferrel Westerlies' was proposed by F. K. Hare in honour of W. Ferrel (see p. 139). The heavy black lines denote reversals of the vertical temperature gradient of the tropopause and stratopause. Summer and winter refer to the northern hemisphere.

Figure 2.16 Mean zonal (westerly) winds (solid isolines, in knots; negative values from the east) and temperatures (in °C, dashed isolines), showing the broken tropopause near the mean Ferrel jet stream.

Source: After Boville (from Hare 1962). Notes: The term 'Ferrel Westerlies' was proposed by F. K. Hare in honour of W. Ferrel (see p. 139). The heavy black lines denote reversals of the vertical temperature gradient of the tropopause and stratopause. Summer and winter refer to the northern hemisphere.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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