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Many types of barometer makes for measuring air pressure.

More about weather instruments.

Simple Mercury Barometer

A barometer makes atmospheric pressure measurements.

The pressure tries to flatten you with the weight of several miles of air above you - YES, AIR DOES WEIGH SOMETHING.

How much?  Think of a vertical box on Long Island, 1 foot square (not very big) going up to the top of the atmosphere.  There would be over 2000 pounds of downward force in that box.

In simple terms, air pressure is how much weight the Earth's atmosphere exerts on anything inside it.  It's an essential part of meteorology, weather forecasting, and many other fields of science and engineering to measure air pressure.

Changes in air pressure are critical in determining weather patterns, and meteorologists closely monitor pressure trends to forecast weather events and help people prepare.  More on this below.

There are several types of barometers available to fit different applications and needs, and they're important tools for measuring air pressure.

Air pressure science

The sea-level pressure ranges from 27 inches to 31 inches of mercury, or 95 to 105 kPa for you metric types and air pressure can be measured with several types of barometers.  Here are some of the most common types:    

-A mercury barometer uses a glass tube filled with mercury at one end.  A vacuum is created above the mercury in the tube by placing the open end in a container of mercury.  When the air pressure changes, the mercury rises or falls inside the tube, providing a pressure measurement.

-Aneroid barometers use a small, flexible metal box that's sealed and has most of the air removed.  A metal box expands or contracts when the air pressure changes, and this movement is amplified by levers and gears to measure the pressure.

-A digital barometer measures air pressure with electronic sensors and displays the results on a screen.  Often used in weather stations and other applications where pressure needs to be monitored constantly.

-A barograph records changes in air pressure over time with a rotating drum and a pen.  Typically, the drum is covered in paper, and the pen is attached to a lever that moves up and down as the pressure changes.  

Interpreting the Air pressure measurements a barometer makes

Weather patterns and conditions can be affected by changes in air pressure.   Here are some examples:

-A high-pressure system is where the air pressure is higher than the surrounding area.  A high-pressure system usually means clear skies and calm weather, since the high-pressure zone prevents clouds from forming, more sun, higher temperatures, and fewer winds. 

-A low-pressure system is where the air pressure is lower than the surrounding area.  Because low-pressure zones allow warm, moist air to rise and cool, they usually cause cloudy, rainy, stormy weather, or snow... and wind power.

-Differences in air pressure between adjacent regions can cause pressure gradients, which can cause wind to move from high-pressure zones to low-pressure zones.   Pressure gradients can affect wind strength and direction. 

-Fronts are boundaries between air masses with contrasting characteristics, like temperature, humidity, and pressure.  Precipitation, thunderstorms, and other severe weather can result when a cold front collides with a warm front.  Along fronts is where you usually find thunderstorms, precipitation, or other severe weather, such as when a cold front collides with a warm front.

I won't even mention barometric pressure headaches and arthritis.  You might not be able to rely on these broad (synoptic) generalizations if you live near big hills.  Other features, called mesoscale (smaller than synoptic) patterns, can mess with prevailing conditions.

Now, what do we use to measure the pressure?

Types of barometer makes

Different types of barometers make different measurements.  We have more fundamental differences than just digital barometers, stationary barometers, and handheld barometers.

What is the height above sea level?

Nearly all barometer makes display the pressure and can be adjusted for altitude, your position on elevation maps. Why?  Because Denver, for example, is a mile in the air, so the atmospheric pressure there is ALWAYS lower than Los Angeles.

Anyhow, it gives you a reading of the pressure caused by the current weather system AS IF you were at sea level.  

Aneroid Barometer Diagrams

In most cases, scientific barometers are electronic, such as those used in environmental data logging projects.

Airplane altimeter

There are two gold electrodes configured as a capacitor inside a vacuum, and pressure causes the capsule to deform, causing a change in capacitance that can be measured and converted into units of pressure.  

There are other types of barometers that use simpler principles and generally respond to changes in air pressure in a container without any air inside.  For instance, take a look at one of those glass water barometers.

Pilots use these kinds of barometers shown here, called altimeters, to determine the altitude of their aircraft.

Barometers (such as the barographs noted above) are also used to note pressure tendency. How much has it changed over the last three hours, up, down, or stayed the same.

Barometer Information


Search this site for more information now.

Barometer pictures and science gifts:

You can find pictures of barometers on US or Canadian eBay or on a retail web page - including electronic, aneroid and liquid-filled models.  Also, Wikipedia has photos and info.

See the StuffInTheAir homepage to learn more about air and the weather.

Go back from Barometer Makes to the Weather Equipment web page.

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