July 24

What Is Barometric Pressure?



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Can you sense changes in the weather? Or maybe someone you know has such innate sensitivity to these changes that they’re able to predict a storm coming from the distance, or perhaps they experience migraines or body aches prior to and during certain weather changes. These “feelings” aren’t merely wives tales, rather this ability and awareness is a natural phenomenon. Here, we will explain what barometric pressure is, what it can tell us about the weather, and how it is used in weather forecasting.

What Is Barometric Pressure?

Barometric pressure, also referred to as atmospheric pressure, is the measurement of the “weight of the air,” as it presses down on the earth’s land and water surfaces, which typically coincides with changing weather conditions. Thus, lower barometric pressures indicate inclement weather, whereas rising barometric pressure readings signal improved weather conditions.

These varying readings are impacted by temperatures, wind, altitude, humidity levels, and their effects on gravity. Barometric pressure is measured using a barometer. A barometer works very similar to a mercury thermometer, but instead of temperatures, it measures units of air pressure, also referred to as atmospheres, or atm.

How Is Barometric Pressure Measured

Because there are so many factors that impact barometric pressure, the standard, or normal barometric pressure readings used by meteorologists are based at sea level. The normal readings range between 970 millibars and 1050 millibars. A single atmosphere equals 1013 millibars (MB), and when translated into mercury readings is equivalent to 760 millimeters of quicksilver.

In most of the meteorology books and diagrams pertaining to the Earth’s atmosphere describing it as a massive ocean of air made up of multiple layers that extend for hundreds of miles. However, scientists are only able to measure upwards of 25 miles with any amount of accuracy, and the atmospheric layer of air that is crucial to life is just over three miles high.

Naturally, in higher altitudes, the weight of air changes, and although people often perceive these elevations as having less oxygen, that’s not necessarily correct. Air weight measurements are defined by the amount of oxygen, nitrogen, and other gases, as well as the pressure and density of these elements. A simple analogy often used is the comparison of air and water in that we swim through air in the Earth’s atmosphere, much like we swim in the ocean. Take for instance, a bucket of water. If you puncture the bucket near the top of the water line, you’ll notice a slow dribble of water. On the other hand, a hole near the bottom of the bucket would cause the water to flow out much more rapidly The water composition is the same throughout, but the pressure of water varies greatly between the two holes.

Thus, compare that to the amount of air pressure our bodies, lungs, and bloodstream feel at different altitudes, hence hypoxia, altitude sickness, and so on.

How A Barometer Helps Predict The Weather

A barometer can actually help you predict the weather throughout the day as it detects even the smallest fluctuations in air pressure. In fact, many barometers are designed to be quite user-friendly. For instance, a barometer with a dial face often has the words “Stormy,” “Rain,” “Fair,” “Change,” and “Very Dry” stamped around the face and the dial will rotate accordingly with air pressure changes.

These labels help you see the exact air pressure and, at a glance, it tells you what exactly that means in terms of how it feels outside. So rather than heading off for a run and getting stuck in a storm, you could get a workout in at home.

What Are High and Low Pressure Systems?

You’ll often hear meteorologists refer to low-pressure and high-pressure systems, when forecasting the weather. A low-pressure system, also referred to as a depression, indicates turbulent weather conditions and usually involves cloudy skies, rain, snow, or storms. On the other hand a high-pressure system is indicative of clear skies and nice, calm weather. 

These two pressure systems are associated with vertical air flow as well as its direction. So, in a high-pressure system, the air sinks and flows outward and in a low-pressure system, the air rises and flows inward.

Basically, in a low-pressure system, the air is moving upward and internally within a specific area. As air rises, it also cools and results in water vapor, condensation, and the formation of clouds and rain or snow. In contrast, when the air flows down and is dispersed outwardly, it generally results in a warm, dry atmosphere and blue skies.

How Altitude Affects Barometric Pressure

In addition to weather conditions affecting barometric pressure, altitude is another component. Since barometric pressure is measured by the amount of air above you, in higher altitudes, these pressure readings are lower because the air is thinner and there is also less gravity.

For these reasons, a barometric pressure meter is not only useful in measuring weather and altitude, but also for determining how high an airplane is flying. As such, you’ll find a barometer inside every plane’s cockpit as part of the standard instrument panel. It’s essential to flying and landing a plane safely at its destination.

How Barometric Pressure Affects Humans

As far as people go, barometric pressure is important to monitor, not just for comfort, but also for safety. Sudden or extreme barometric pressure changes can cause physical ailments for some people. This is why pilots and flight attendants take health precautions and wear certain types of clothing to protect themselves.

Likewise, barometric pressure changes have been linked to things like migraines, high-altitude sickness, the bends, or increased joint pain. That’s why old sailors would sometimes try to use their knees and other joints as sensitivity monitors in determining what the weather would be in the coming hours.

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