Variation in atmospheric pressure:

The atmospheric pressure decreases as we go up. The atmospheric pressure on mountains is lower than at sea level. At a height of about 30 km, the atmospheric pressure becomes only 7 mm of mercury which is approximately 1000 Pa. It would become zero at an altitude where there is no air. Thus, we can determine the altitude of a place by knowing the atmospheric pressure at that place.

Atmospheric pressure may also indicate a change in the weather. On a hot day, the air above the Earth becomes hot and expands. This causes a fall in atmospheric pressure in that region. On the other hand, during cold chilly nights, the air above the Earth cools down. This causes an increase in atmospheric pressure.