Physical Geography (Unit 2)
Wind System
- Heating by the Sun
- Rotation of earth on its axis
The formation of the wind system begins with the sun’s radiation, which is absorbed differently on the earth’s surface. The earth’s surface is heated differently because of scenarios like cloud cover, mountains, valleys, water bodies, vegetation and desert lands.
As a result of this uneven heating, there are bound to be earth surfaces that vary a lot in temperature. Air on surfaces with higher temperatures
will then begin to rise because it is lighter (less dense). As the air rises, it creates low atmospheric pressure. Air on surfaces with cooler temperatures sink (do not rise). The sinking creates higher atmospheric pressure. This behaviour or warm gases or liquids moving upward and being replaced by cooler particles is called Convection. The energy moving during convection is called convectional current.
Anywhere and each time there are differences in atmospheric (air) pressure, there will be winds, because air will move from the high pressure area to the low pressure area. It also means that winds may be even stronger where the difference in the air pressure is greater.
A good example is how a tropical depression forms, where warm air over hot tropical waters rise, and high pressure cold air quickly rushing to fill the space.
Types Of Winds
Local Winds
Local winds are those that are created as a result of scenery such as mountains, vegetation, water bodies and so on. They can move from mild to extreme winds in just hours. Good examples of local winds are sea breezes and land breezes, and mountain and valley breezes. Local winds cover very short distances.
Permanent Winds
They are really large air masses that are created mainly as a result of the earth’s rotation, the shape of the earth and the sun’s heating power.
Trade winds:
This is the belt extending as far as 30° north and south latitude of the Inter-Tropical Convergence Zone (ITCZ).
Westerlies:
This is the belt extending from 30° to 60° latitude from the ITCZ.
Easterlies:
This belt covers from 60° latitudes to the north and south poles.
Coriolis Force
As the winds blow from the north and south towards the equator, their flow path is deflected by the earth’s rotation. When moving objects are viewed in a reference frame, their path looks curved. This is the coriolis effect, and it is simply caused by the earth’s rotation. This effect makes wind systems in the southern side of the equator (southern hemisphere) spin clockwise and wind systems in the northern side (north hemisphere) spin counter-clockwise.
Wind Measurement
Winds come in all directions or speeds. They are measured by their directions and speeds.
Depending on the cause of the winds, they can blow in many directions. Some good examples of wind direction are the Easterly winds, which blow from east to west, and westerly winds which blow from west to east. There are also winds that blow from the north, southwards and also those from the south blowing northwards.
Anemometers
Anemometers measure the direction of winds.
The Wind Vane
Another instrument in wind measurement is the wind vane.
Front
This is the boundary between two large air masses. It is the meeting point between cold dense air and warm light air. At a front, warm is pushed upwards because of its less density. A front can be very intense or mild, depending on the temperatures of the two air masses meeting. Air masses with extreme temperatures will produce a fierce front, whereas air masses with little temperature difference will produce very mild front.
Prevailing Winds
This is simply a term used for winds that are most frequent in its’ direction and speed over a specific geographic region. Different geographic areas have different prevailing winds because of the factors that shape them.
Jet Stream
This was discovered in 1940’s (during the World War II). Pilots noticed that their flying speeds were significantly reduced when flying against some areas in the upper troposphere. Jet streams can be found in the upper troposphere. They are very strong winds.
Beaufort Wind Force Scale
In 1805, a British Naval Officer invented this scale to measure wind force. The scale has reading of 0 up to 12 to classify wind force.
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