The air around us is made up of tiny molecules that are constantly moving around. Air pressure is the force from those molecules pushing against anything that is around them. A simple example of this is pumping up a bicycle tire with air, which increases the number of air molecules in the tire pushing against the inside of the tire, expanding the size of the tire so you can ride your bike comfortably down the road.
Atmospheric pressure is the force of the air in the atmosphere pushing on everything it touches – so wherever you are standing, the air in our atmosphere is pushing down on you. When you are at the lowest level of our atmosphere, also known as sea level, the air is pushing down on you with an average force of 14.7 pounds per square inch (PSI)! As you go higher into the atmosphere there is less atmospheric pressure, because there are fewer molecules of air above your head, the force of the air pushing down on you is less.
How Meteorologists Measure Air Pressure
Meteorologists use a barometer to measure the amount of atmospheric pressure. That is why you may see or hear meteorologists refer to atmospheric pressure as barometric pressure. At sea level, the average barometric pressure is 29.92 inches (in.) or 1013.25 millibars (mb). By measuring the change in barometric pressure over time, meteorologists can understand if the weather is going to improve or worsen. In general, higher barometric pressure is associated with good weather while lower barometric pressure is associated with bad weather.
Air Pressure on a Map
When looking at a weather map or chart, you may see one or more ‘H’ or ‘L’ shown on the map. The ‘H’ represents an area where air is sinking and pushing down on the surface with more force causing a higher barometric pressure, while the ‘L’ represents an area where air is rising and pushing down on the surface with less force causing a lower barometric pressure. In general, higher barometric pressure is associated with good weather with fewer clouds while lower barometric pressure is associated with bad weather with more clouds – and possibly rain or even snow if it is cold enough!
Why do your ears pop driving into the mountains, riding in an elevator, or taking off on a plane?
Whenever the atmospheric pressure increases or decreases quickly around us, our body takes time to adjust. One example of our body adjusting to a quick change in atmospheric pressure is how our ears ‘pop’. This is because the air pressure inside our ears is momentarily different from the air pressure outside our ears. Our ears ‘pop’ as the air pressure becomes the same inside and outside our ears and we can hear that ‘pop’ happen.
Simple Air Pressure Exercise
The WeatherFlow WEATHERmeter has a barometer and can measure the atmospheric pressure around us so you can track how the atmospheric pressure is changing around you. In this experiment, you will learn how increasing and decreasing air pressure changes barometric pressure.
- A gallon or quart-sized zip lock bag
- The handheld WEATHERmeter
- Take a gallon or quart-sized zip lock bag, stick the WEATHERmeter in it (on and showing air pressure in the Wind & Weather Meter app on your smartphone or tablet), blow up the bag, and seal it.
- Push on the bag and watch how air pressure reading increases. Stop pushing on the bag and watch how air pressure decreases.