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On a clear summer day, turbulence caused by solar heating is most pronounced..
  • A
    during the early afternoon.
  • B
    immediately after sunset.
  • C
    about midmorning.
  • D
    during the early morning hours before sunrise.

Refer to figure.

Within the friction layer, we can identify two types of turbulence:


Expected on warm summer days when the sun heats the earth's surface unevenly. Certain surfaces, such as barren ground, rocky and sandy areas, are heated more rapidly than are grass covered fields and much more rapidly than is water. Insolation gives rise to convection currents - with warm air rising and cooler air descending, which are responsible for bumpy conditions as an airplane flies in and out of them.

- Thermal turbulence is greatest around 1500 hrs on clear sunny days (when the highest temperatures are reached) - In weather conditions when thermal activity can be expected, many pilots prefer to fly in the early morning or in the evening when the thermal activity is not as severe.


Friction between the air and the ground, especially irregular terrain and man-made obstacles (such as hills, mountains, coasts, trees and buildings), causes eddies and therefore turbulence in the lower levels.

- This kind of turbulence will increase as the wind speed increases.

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