Atmospheric pressure is caused by the weight of the air above pressing down. It is measured in millibars using a barometer. There are mercury and aneroid barometers. Pressure varies due to altitude, temperature, and water vapor content. Higher altitudes, warmer temperatures, and more moisture all result in lower air pressure. The earth's rotation also affects pressure, creating semi-permanent high and low pressure belts globally.

1. ATMOSPHERIC PRESSURE

2. Introduction
Air exerts pressure on everything on the Earth ‘s surface
This happens because the upper layers of the atmosphere rest on the lower layers

Atmospheric pressure can be defined as the force exerted by a column of
air due to its weight at a particular place on the earth ‘s surface .

3. Introduction
◦ The unit in which air pressure is measured is called millibars
• The instrument used to measure atmospheric pressure is called barometer
◦ There are two types of barometer
Mercury
barometer
Aneroid
barometer

4. Mercury
barometer
A mercury barometer
is used to calibrate
and check aneroid
barometers

5. Aneroid
barometer
A non-liquid
barometer called the
aneroid barometer is
widely used in
portable instruments
and in aircraft
altimeters because of
its smaller size and
convenience.

6. FACTOR AFFECTING
ATMOSPHERIC PRESSURE

7. Introduction
◦ Atmospheric pressure on the earth’s surface it is not uniform
◦ It varies form place to place and time to time
◦ There are three main factors –
Altitude Temperature Water vapour

8. ALTITUDE

9. Altitude
◦ Air pressure is the highest at sea level and decreases with altitude
◦ In the sky above the density of air decreases and so does the pressure exerted by it .

10. TEMPERATURE

11. Temperature
◦ When Temperature increases the air expands and its density decreases as a result air
becomes lighter and exerts less pressure

12. WATER
VAPOUR

13. Water vapour
◦ Air containing more water vapour is lighter than air which has little or no water
vapour , and thus the air pressure decreases

14. Types of air
Hot air Cool air
Moist air Dry air

15. Hot and cool air
Hot air
◦ When the temperature increases the
air expands
◦ Density decrease
◦ The air becomes lighter
Cool air
◦ When the temperature decreases
◦ Density increase
◦ The air is more heavier

16. Moist and dry air
Moist air
◦ Air which contain more water vapour
◦ Lighter
Dry air
◦ Air which contain lessor no water
vapour
◦ Heavier

17. PERMANENT PRESSURE
BELTS

18. Introduction
◦ The horizontal distribution of atmospheric pressure is not uniform all over the globe
◦ It varies from place to place
◦ It is also affected by temperature
◦ But majorly it varies due to the rotation of the earth
◦ There are four important pressure belts

20. Thank you