Vertical divisions of The Atmosphere

Vertical motion of air is an important factor in the development of weather.

Sometimes rising air is made visible by the development of clouds or by the rising dust in dust whirls.

Violent vertical motion can be seen in tornados. At other times rising air may occur in the absence of any visual clue. Subsiding air is normally relatively gentle and associated with clear conditions, except when in association with mountain waves and downburst activity from convective clouds.

The strength of vertical motion in the atmosphere is largely determined by the vertical stability of the atmosphere.

A stable atmosphere will tend to resist vertical motion, while an unstable atmosphere will assist it.

When the atmosphere neither resists nor assists vertical motion it is said to have neutral stability.

Vertical motion and instability are responsible for atmospheric turbulence and cloud formation.

The Significance of Tropopause Height 

The significance of the tropopause height is that it usually marks: 

  • the maximum height of the significant cloud. 
  • the presence of jet streams. 
  • the presence of Clear Air Turbulence (CAT). It is now referred to as TURB. 
  • the maximum wind speed. 
  • the upper limit of most of the weather 

 Divisions of the atmosphere¨illustrating the variations of temperature with height.

Temperatures 

The temperature in the troposphere increases from the poles to the Equator. 

The temperature in the lower stratosphere increases from the Equator to the poles in summer but reaches max temperature in mid-latitudes in winter. 

Atmospheric Hazards 

As aircraft operating altitudes increase, so concentrations of OZONE and COSMIC RADIATION become of greater importance to the aviator. 

Above 50 000 ft, normal concentrations of ozone exceed tolerable limits and air needs to be filtered before entering the cabin. The heat of the compressor system will assist in the breaking down of the ozone to an acceptable level. 

Cosmic radiation is not normally hazardous, but at times of solar flare activity, a lower flight level may be necessary. 

Advances in meteorological forecasting and communications should result in pilots receiving prompt and accurate information regarding high altitude hazards, but it is important that they should be aware of these hazards and prepared to take the necessary re-planning action. 

The above figure shows atmospheric pressure decreasing more rapidly with height in the lower layers. At an altitude of 18 500 feet (500 hPa) one-half of the atmosphere’s molecules would already be below you. That is, half of the mass (weight) of the atmosphere is contained in the layer below 500 hPa.

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