Average air (or atmospheric) pressure at sea level is 1.03 kilograms per square centimetre (14.7 pounds per square inch). Although it's easy to forget, air molecules all weigh something, and their combined weight pressing down is what causes this pressure. At sea level, the column~of air above you weighs about a ton. As you gain altitude, the number of air molecules above you decreases, and therefore so does the air pressure. The lowest atmospheric pressure on Earth can befound at the summit of Mount Everest, where it's just 0.3 kilograms per square centimetre (4.4 pounds per square inch).
- Alexandra Cheung.
In essence, a barometer is a scientific device that is instrumental in meteorology to assist an accurate weather forecast. It is used to measure that atmospheric pressure (also known as barometric pressure or air pressure - (thus its name; the barometer). The pressure tendencies in the air can help forecast weather changes. Barometers have essentially been around since the 1700s, and some documents suggest that the barometer was even possibly around even before that. Earlier, it was thought that air had no weight and therefore could not be used as an indicator of anything. With time, however, researchers soon understood that not only does air bear weight, but that it could help forecast significant climate changes as well.
The first every barometer was invented in 1643 by Evangelista Torricelli. It was popularized as "Torricelli's tube" and is widely viewed as the predecessor to all barometers invited after the first attempt.
The barometer has been used regularly in weather forecasting since about the 1800s. When used in conjunction with wind observations, barometers can predict the weather reasonably well. These predictions (known as a weather forecast), however, were usually short-term to begin with. With time, weather forecast technology progressions were made and barometers today can predict long-term weather, and do it quite accurately.
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What is barometer? - a mechanical device that measures the pressure of ambient air changes.
There are many types of barometers. Reading a barometer is easy with simple visual representations of the weather reflected by current air pressure.
Over the years, various barometers have been invented and put to use. There are some that are more widely used than the other, with the mercury barometer being the one that is used the most. Some of the most widely used barometers are:
Mercury barometer: A mercury metal liquid barometer which is equipped with a glass tube that is closed on one end. At the base, there is a reservoir filled with mercury. Thanks to the mercury's weight, a vacuum is created in the barometer tube's top and the mercury in the tube then adjusts till the weight of the column with mercury balances the air force that is exerted on the reservoir. When the ambient air pressure is high, there is more force on the barometer reservoir and the mercury is forced higher up in the column. On the other hand, when the pressure is low, the mercury drops to a lower level.
The mercury barometer has been around for centuries but design changes are continually made to make the weather barometer instrument better, more sensitive along with being simpler to work with and easier to carry. A mercury barometer is further available in many more operation types. Most variations arise from the different techniques that are used for measuring the height of the mercury case of a weather barometer. While other liquids can also be used in the barometric device, mercury is the most common. The density of mercury allows a barometer's vertical column to be of a manageable size.
Water-based barometer - water barometer or weather ball barometer: which is based on the 'storm glass' invented by Goethe, the weather ball barometer is made up of a glass container with a sealed body that is half filled with water. A narrow tube connects the liquid barometer container's body below the water level and tends to rise above the level of the water in the barometric container. The tube is open to the atmosphere. When the atmospheric pressure is lower than it was back when the water body was sealed, the water level in the barometric tube rises above the water in the body and when the pressure is higher, the water level in the drop will be lower than the level of water in the body.
Aneroid barometer: This type of barometer, used less frequently than the others, makes use of a tiny flexible metal box known as the aneroid cell. It is made from an alloy of copper and beryllium. The barometric capsule is prevented from collapsing with the help of a very strong spring. Tiny changes in the external air pressure make the capsule expand or contract and this expansion or contraction drives the mechanical levers so that the small movements of the capsule are amplified and then displayed on the barometer's face.
One important type of an aneroid barometer is a barograph. It is used to monitor pressure and the regular pointer in the barograph is replaced with a pen. The barometer produces a foil chart or paper that is called a barogram. The barogram records the atmospheric pressure over time.
There are other, more unusual types of barometers, but the 3 mentioned here are most widely used.
Recording changes in air pressure are one of the prime and most commonly used ways to forecast weather and potential changes because weather patterns change mostly due to changes in regions with very high and low pressures.
A slow rise in the air pressure, over 1 or 2 weeks, is usually an indicator of weather that has settled and will be consistent for a long time. Sudden drops in barometric pressure, recorded over a few hours, usually forecast that a storm is approaching. The storm will not last long, but will being heavy rains and strong winds with it.
A careful study of the pressure recorded on a barometer can forecast weather, and even people who know very little about meteorology can predict the weather to a certain extent. Some simple barometer guidelines:
- a consistent decrease in atmospheric pressure indicates rain, winds and a possible storm.
- a consistent rise in pressure indicates dry, colder weather.
- a slow, consistent and average fall in air pressure is suggestive of a low pressure area passing by. There would be no changes in the weather from where the pressure is being measured.
- a quick drop in the pressure over a very short period of time is indicative of a storm within the next 6 hours.
- a quick rise in pressure is indicative of a short period of good, clear weather.
- a large and consistent rise in pressure is indicative of a long period of clear, good weather.
In very simple terms, a rising barometer can indicate anything from clear skies to storms, winds or frost, and a falling barometer reading is generally a sign of an upcoming storm.
A barometer reading that is steady and consistent usually mean clear, sunny skies.
Barometers can also be made at home and many students opt for making a good, working barometer for their science project.