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Name: George
Status: educator
Grade: 9-12
Location: FL
Country: USA
Date: Spring 2012


Question:
I teach classes in weather and air navigation. I am reviewing a document on Weather Forecasting that includes a brief section on weather instruments for surface observations. Do you have a document(s) you can refer me to that explain the manufacture of the barometer aneroid? In other words, what I am trying to determine is exactly what the pressure is inside the aneroid. In aviation barometric altimeters, most of the books say that the aneroid is pressurized to STP (Standard Atmospheric Pressure and Temperature) which in America is 29.92 in. Hg. at 59 Degrees F. Most weather texts however state the meteorological barometer as having an evacuated (vacuum), or partially evacuated chamber. Is there a different standard for weather instruments vs. aircraft altimeters?


Replies:
George,

Both aneroid barometers and altimeters have an evacuated chamber; the measurement device (the evacuated chamber) is essentially identical in both. Both are adjusted to sea level pressure. Where you read "that the aneroid is pressurized to STP" simply means that it was adjusted to sea level and STP. This is done for both the barometer and the altimeter.

The two devices are used differently. A barometer reading shows the atmospheric pressure at sea level, whereas an altimeter shows the altitude that corresponds to the sea level pressure measured.

David R. Cook Meteorologist Climate Research Section Environmental Science Division Argonne National Laboratory


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