Significance Of Atmospheric Pressure


 
 
Concept Explanation
 

Significance Of Atmospheric Pressure

Atmospheric Pressure, Winds and Air Masses: Air, being a physical substance, is an admixture of several gases present in the atmosphere and, thus, it has its weight. Air pressure is defined as total weight ofamass of column of air above per unit area at sea level (unit area being one square inch, in square foot, one square centimetre, one square metre etc.). The atmospheric pressure is the highest at sea level. It exerts the weight of 14.7 pounds on the area of one square inch at sea level or 1,034 grams (about one kilogram) per square centimetre. One can imagine as to how much weight of overlying air is being carried by every man daily, but he does not feel such enormous weight on his head and shoulders because the air present inside human body exerts equal amount of outward pressure which balances the inward atmospheric pressure.

Measurement of Air Pressure: The atmosphere rests on the earth's surface owing to the gravitational pull of the earth. Hence, it exerts its weight as pressure on the earths' surface. Atmospheric pressure is thus the weight of the column of air at any given place and time. It is measured by means of an instrument called a barometer. It is measured As a force per unit area. The units used by meteorologists for this purpose are called millibars (mb), One millibar is equal to the force of one gram on a square centimetre. A pressure of 1,000 millibars is equal to the weight of 1.053 kilograms per square centimetre. In other words, it will be equal to the weight of a column of mercury 75 centimetres high, To be exact, the normal pressure at sea level is about 76 centimetres (1,013.25 millibars). However, it fluctuates on either side of this value.

The distribution of atmospheric pressure is shown on a map by isobars. An isobar is an imaginary line drawn through places having equal atmospheric pressure reduced to sea level. The spacing of isobars expresses the rate and direction of the pressure changes and is referred to as pressure gradient. Close spacing of isobar indicates a strong pressure gradient, while wide spacing suggests a weak gradient. The pressure gradient, therefore, may be defined as the decrease in pressure per unit distance in the direction in which the pressure decreases most rapidly. There are two types of pressure systems - high pressure and low pressure.

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