Understanding Atmospheric Pressure
* Pressure and Altitude: Atmospheric pressure decreases with altitude. This is because the weight of the air above a given point pushes down on the air below.
* Millibars (mb): A millibar is a unit of pressure. Standard sea-level pressure is about 1013.25 mb.
Calculation
1. Ratio: The fraction of the atmosphere below the aircraft is simply the ratio of the pressure at 700 mb to the pressure at sea level:
Fraction = 700 mb / 1013.25 mb ≈ 0.69
2. Percentage: To express this as a percentage, multiply by 100:
Percentage = 0.69 * 100% ≈ 69%
Conclusion
Approximately 69% of the Earth's atmosphere is below an aircraft flying at the 700 mb level.
Important Notes:
* Simplification: This calculation makes a few simplifying assumptions:
* It assumes a standard atmosphere, which isn't always accurate.
* It doesn't account for variations in pressure due to weather conditions.
* Weather Impact: Actual pressure at a given altitude can vary greatly due to weather systems.
* Altitude Equivalents: While the 700 mb level is a common aviation reference, its actual altitude can vary. It's roughly equivalent to about 10,000 feet.
