Ambient Pressure

The term ambient pressure refers to the pressure of the surrounding air, gas or liquid in contact with an object in a specific location. Ambient pressure differs underwater and in the atmosphere. When in the atmosphere, the pressure drops as the altitude increases. When underwater, ambient pressure is a combined force with hydrostatic pressure as well.

Near Earth’s surface the pressure decreases with height at a rate of about 3.5 mbar for every 30 metres (100 feet). However, over cold air the decrease in pressure can be much steeper because its density is greater than warmer air. The pressure at 270,000 metres is comparable to that in the best man-made vacuum ever attained. At heights above 1,500 to 3,000 metres (5,000 to 10,000 feet), the pressure is low enough to produce mountain sickness and severe physiological problems unless careful acclimatization is undertaken.

The highest and lowest sea-level pressures ever recorded are 32.01 inches (in the middle of Siberia) and 25.90 inches (in a typhoon in the South Pacific).