First Alert Weather 101: What is pressure?
HONOLULU (HawaiiNewsNow) - The terms “high pressure” and “low pressure” almost always find their way into the vocabulary of weather presenters across the globe.
But what exactly is pressure? What is a pressure system?
And why should anyone care?
The difference between high and low pressure is sometimes the difference between sunshine and downpours.
In weather speak, pressure can be simplified to the weight of all the air particles above you. On average, 14.7 pounds of air are above you at any given time.
We do not feel the weight of air above us because our bodies are built to withhold the added downward force of the atmosphere. This is also true for almost all life at the surface of the earth. Life evolved to sustain the weight of the entire atmosphere.
Pressure can also be measured in other fluids. For instance, the pressure at the bottom of the ocean is several orders of magnitude larger than that of the entire atmosphere.
Water is much heavier than air. When combining the weight of all water particles above the bottom of the ocean, you are greeted with a much stronger downward force than that of the weight of all the air above the surface of the earth.
On average, the weight of the atmosphere is 14.7 pounds. However, that weight fluctuates regularly. This fluctuation is a good starting point for understanding high and low-pressure systems.
Visualize this:
- A low-pressure system is when there is less air above you than the global average. Air is missing above your head.
- A high-pressure system is when there is more air above you than the global average. Air is piling up on top of your head.
Pressure also relates to one of the most important aspects of weather: upward motion.
Almost all weather is created by the upward motion of air within the atmosphere, including thunderstorms, tornadoes, hurricanes, and blizzards.
High pressure > calm weather
High pressure is typically associated with less weather because of the larger amount of air in the atmosphere.
The surplus of air particles makes it harder for air to move upwards. This, in turn, leads to calm weather and sunny skies.
Low pressure > rain and storms
Low pressure is typically associated with active weather because of the deficit of air particles in the atmosphere.
The deficit of air above makes it easier for air to move upwards. This, in turn, can lead to messy weather, rain, and thunderstorms.
The atmosphere is fluid and constantly fluctuating. However, learning these meteorological concepts is a starting point for understanding the complexities of the atmosphere.
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