Atmospheric Pressure | CUET PG Geography | Notes

• Atmospheric Pressure is nothing but a column of the weight of air in a particular unit area from the mean sea level to the top of the atmosphere.
• Atmospheric pressure is also called barometric pressure.
• The pressure is measured in force per unit area.
• The atmospheric pressure is expressed in the ‘millibar’’ or ‘mb’ unit.
• The atmospheric pressure can also be measured with the help of a mercury barometer.
• To check the pressure the height of the column of the mercury should match the weight of the column of the atmosphere in the mercury barometer, and we can also measure the pressure with the help of an android barometer.
• The atmospheric pressure is stated as kilo-pascals at the application level.
• The mercury barometer or aneroid barometer is used to measure the atmospheric pressure.
• The pressure decreases rapidly with height in the lower level of the atmosphere.
• The horizontal pressure gradient force is much smaller than that of the vertical pressure.
• In the center, the lowest pressure is the isobars of the low-pressure is encircled by one or more isobars.
• In the center, the highest pressure is the isobars of the high-pressure is encircled by one or more isobars.
• Isobars are connecting the lines and it has equal pressure.

Units to Measure Atmospheric Pressure

There are seven different ways to measure atmospheric pressure.

• Millimeters (Inches of mercury)
• Pounds per square inch (psi)
• Dynes per square centimeter
• Millibars (mb)
• Kilopascals

Standard Sea Level Pressure in Units

• The atmospheric pressure on the surface of the earth in millimeters is 760 or 29.9 inches of mercury.
• The atmospheric pressure on the surface of the earth in pounds per square inch is 14.70
• The atmospheric pressure on the surface of the earth in dynes per square inch is 1,013.25 × 103.
• The atmospheric pressure on the surface of the earth in millibars is 1,013.25.
• The atmospheric pressure on the surface of the earth in kilopascals is 101.325.

Pressure Gradient

• The change in the rate of pressure regarding distance is called the pressure gradient.
• If the pressure gradient is negative it is known as the force density.
• The pressure gradient is expressed in units of pascals per meter.
• Both path and geometry of the column are not the same.
• The horizontal pressure gradient force is directed from higher toward lower pressure.
• To make wind, the pressure gradient acts as the main force in the air.

Pressure Belts

• There are two patterns over the earth: Alternate high and Low pressure.
• There are seven pressure belts in the atmospheric pressure.
• There are two subtropical highs in north and south and two subpolar lows in north and south and the two polar highs in north and south except for the equatorial low.
• The pressure belts oscillate with the movement of the sun.
• They move southwards in the winter season and they move northwards in the summer in the northern hemisphere.
• On being light the equatorial region gets too much heat and warmth. The rise in the flow of air in the equatorial region generates a low pressure.
• Equatorial Low: The low equatorial is found near the equator. The pressure in the sea level is low.
• Subtropical Low: The subtropical low is present in the high-pressure areas, this reason is present in 30 degrees north and 30 degrees south.
• Subpolar Lows: This region is present in the low-pressure belts particularly in 60 degrees north and 60 degrees south.
• Polar Highs: The Polar highs present are near poles which have high pressure.