Adjusting for altitude pressure primarily involves accounting for the natural decrease in atmospheric pressure as elevation increases. You don't physically "adjust" the pressure of the atmosphere itself, but rather calculate the expected pressure change due to your altitude, often for calibrating instruments or understanding conditions at a specific elevation.
Atmospheric pressure is the weight of the air column above you. As you gain altitude, there's less air above you, so the pressure decreases. This pressure difference must be considered in various applications, such as operating scientific instruments, calibrating barometers, or even in activities like cooking or aviation.
Calculating Pressure Adjustment Based on Altitude
To account for the effect of altitude on pressure, you can calculate the expected pressure drop relative to sea level or a known reference point.
Based on scientific observations:
- Pressure drops by approximately 26 millimeters (mm) of mercury for every 1000 feet above sea level.
- This rate can be simplified: 26 mm รท 1000 feet = 0.026 mm per foot.
This rate is crucial because, as noted in the reference from the Wisconsin DNR, it's used to determine the pressure difference solely attributable to altitude.
How to Calculate the Altitude Pressure Difference
To find the pressure difference caused by altitude:
- Determine your altitude in feet above sea level.
- Multiply your altitude (in feet) by the rate of pressure drop per foot (0.026 mm/foot).
Calculation Formula:
| Component | Value/Description |
|---|---|
| Altitude | Your height above sea level (in feet) |
| Pressure Drop Rate | 0.026 mm per foot |
| Pressure Drop | Altitude (ft) * 0.026 (mm/ft) |
The result of this calculation gives you the estimated pressure drop in millimeters of mercury compared to sea level or a standard reference pressure.
Practical Example
Let's say you are at an altitude of 5000 feet:
- Altitude: 5000 feet
- Pressure Drop Rate: 0.026 mm/foot
- Calculated Pressure Drop: 5000 feet * 0.026 mm/foot = 130 mm
This means that, solely due to altitude, the pressure at 5000 feet is expected to be approximately 130 mm lower than the pressure at sea level under standard conditions.
This calculated pressure drop is then used to "adjust" readings from instruments like barometers. For example, a barometer reading taken at altitude might be "corrected" to a sea-level equivalent by adding this calculated pressure drop, allowing for easier comparison of pressure readings from different elevations.
In summary, adjusting for altitude pressure means calculating the pressure difference caused by elevation using a known rate of pressure change per unit of altitude.
