Author:
E-mail:
Rihard Rumnieks
rihard@lanet.lv
Movie:
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Atmospheric pressure
From 00:06:01 To 00:09:00
Mik Romanovsky, Robert Rubin
Latvian Television
Scientific level
As e consequence from barometric formula, barometer, when properly
calibrated, can be used to determine high. An altimeter is an active instrument used to
measure the altitude of an object above a fixed level.
Picture from http://www.nasaexplores.com/show_58_student_st.php?id=03042282815
The traditional altimeter found in most aircraft works by measuring the air
pressure from a static port. Air pressure decreases with an increase of altitude —
about one millibar (0.03 inches of mercury) per 8.23 m close to sea level. The
altimeter is calibrated to show the pressure directly as altitudes.
The reference pressure can be adjusted by a setting knob. This is necessary,
since sea level air pressure varies with the weather. An altimeter cannot, however, be
adjusted for variations in air temperature. Differences in temperature from the ISA
model will, therefore, cause errors in indicated altitude.
The calibration formula for an altimeter, up to 36,090 feet (11,000 m), can be written
as:
where h is the indicated altitude in feet, P is the static pressure and Pref is the
reference pressure (use same units for both). This is derived from the barometric
formula using the scale height for the troposphere.
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The highest sea-level pressure on Earth occurs in Siberia, where the Siberian
High often attains a sea-level pressure above 1032.0 mbar. The lowest measurable
sea-level pressure is found at the centers of hurricanes. Likewise barometer can be
used for .
A storm glass is a type of barometer invented by Admiral Robert FitzRoy. It is
composed of a sealed glass container, filled with liquid, that allows the user to forecast
the weather by observing the appearance of the liquid in the glass. The liquid within
the glass is a mixture of several ingredients, most commonly distilled water, ethanol,
potassium nitrate, ammonium chloride, and camphor.
If the liquid in the glass is clear, the weather will be bright and clear.
If the liquid is cloudy, the weather will be cloudy as well, perhaps with
precipitation.
If there are small dots in the liquid, humid or foggy weather can be expected.
A cloudy glass with small stars indicates thunderstorms.
A storm glass works on the premise that temperature and pressure affect solubility,
sometimes resulting in clear liquid; other times causing precipitants to form.
Speak in images, storm glass was temperature and pressure sensors connected to
analog computer with user friendly display. 
Picture from http://suwa-co.jp/palm/weather/torka_1.htm
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Sites about Atmospheric pressure (also used in explanations):
http://en.wikipedia.org/wiki/Atmospheric_pressure
http://en.wikipedia.org/wiki/Storm_glass
http://www.nasaexplores.com/show_58_student_st.php?id=03042282815
http://en.wikipedia.org/wiki/Altimeter
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