Most people will take a minute to watch or listen to the weather forecast. Often people have heard terms like high pressure system, low pressure and the general thoughts that the weatherman share. It would be interesting to know if the general public really understands many of the terms that are used.
Weather on planet earth changes constantly. The temperatures of the surface of the earth, the temperature of the water and the air in the atmosphere. The winds all play an integral part of creating weather.
So how is that a high pressure weather system form and what does it mean for the people who are affected by it? A high pressure weather is usually associated with clear and sunny weather. In general people are happy to hear about a high pressure system.
There are three things that cause the wind to blow in the direction that it does. These three things are coriolis force, pressure gradient force and friction. The pressure gradient force (PGF) is caused due to the differences in pressure within the atmosphere. The movement happens as the attempt is made to eliminate pressure differences. With no other factors wind would always blow from high pressure to low pressure.
The coriolis force is the rotation of the earth and the constant movement. It is strongest near the poles and not measurable at the equator.
Friction has to due with the terrain on the surface of the earth. Mountains, valleys, bodies of water, flat desserts all have great influences and the winds and therefore on the air pressure and weather.
High pressure is most often caused by subsidence. This happens when the air begins to cool and becomes more dense. This forces it to move toward the ground. The pressure increases here because more air fills the space left from the low. Typically this would keep the clouds away and the sunshine.
Another side effect of subsidence is that it evaporates most of water vapors in the atmosphere. This means that the air is dryer. Dry heat feels better than heat with humidity. This is where the numbers for the heat index become a part of the equation. How hot is it as opposed to how hot does it feel.
So the next time you are looking at the weather map and see that there is a high pressure system, you know that you can look forward to some nice weather and now you also know why.