The air moving away from the High pressure system leaves a “hole” to be filled, so air from above sinks into that “hole”.
Click on image for full size
Windows to the Universe original image
High Pressure Systems
You may have seen a weather
map with a blue H on it. This blue H means there is a high pressure system over that area of the map. Just what does that mean?
There are no exact measurements that would make a system a High. It's all relative! If a certain system is a High pressure system, that means it has higher pressure then the areas around it.
The differences in pressure from one place to another on Earth are what cause wind. You see, air wants to move from areas of high pressure to areas of low pressure. Away from areas of high pressure and into areas of low pressure.
The Coriolis Force also adds rotation to the movement of air. In the Northern Hemisphere, air moves clockwise around a High and counter-clockwise around a Low.
Now the air moving away from the High pressure system leaves a "hole" to be filled, so air from above sinks into that "hole". As the air sinks, water that was in the condensed form (like clouds) tends to evaporate into water vapor. This means the water is not in the condensed form needed to make clouds and precipitation. That's why many people see a blue H on a weather chart and know good weather and clear skies are coming!
You might also be interested in:
Even though we can't see air, it is real and has pressure. The pressure of the atmosphere changes. It is higher at sea level, and lessens as you go higher up in the atmosphere. Some weather systems have...more
Wind is moving air. Warm air rises, and cool air comes in to take its place. This movement creates different pressures in the atmosphere which creates the winds around the globe. Since the Earth spins,...more
How many hurricanes will form this year? How strong will they be? While no one can say for sure, teams of scientists make predictions each year about the strength of the upcoming hurricane season. To make...more
The Walker circulation is an ocean-based system of air circulation that influences weather on the Earth. The Walker circulation is the result of a difference in surface pressure and temperature over the...more
A barometer is a weather instrument used to measure atmospheric pressure. The first barometer was invented in 1643 by Evangelista Torricelli, one of Galileo's assistants. This first barometer used mercury...more
Rainbows appear in the sky when there is bright sunlight and rain. Sunlight is known as visible or white light and is actually a mixture of colors. Rainbows result from the refraction and reflection of...more
The Earth travels around the sun one full time per year. During this year, the seasons change depending on the amount of sunlight reaching the surface and the Earth's tilt as it revolves around the sun....more