What type of pressure system causes most storms

Stormsurf Mobile App. What is a storm? We've determined that swells are made by wind, and wind comes from storms. But what really is a storm? Well, let's start with some basics. Air covers the surface of our planet and has mass, that is, it has weight and volume, and it can be made to move.

That's fairly obvious. But what causes it to move? Our atmosphere is dynamic, and it's temperature constantly changes in response to rotation of the planet, changes in seasons and earth's orbit around the sun. Why is temperature important? Because hot air is less dense than cold air, and when hot and cold air collide, the hot air is forced to rise over the colder air. Cold air typically is dryer than warm air and originates from our planet's poles.

Whenever cold dry air moves away from the poles, it eventually encounters warm wet air moving away from the equator. The warm wet air is forced up and over the cold air. When the warm air is forced up, it causes surface air pressure to drop, sort of like having a small vacuum develop at the earth's surface at the boundary between the two air masses. As the low pressure intensifies, storms or hurricanes can be formed.

Low pressure systems rotate in a cyclone which is characterized by motion in a counter-clockwise direction in the northern hemisphere clockwise in the southern hemisphere. Rotation is initiated by the rotation of the earth. A high pressure system is colder air moving from the upper layers of the atmosphere towards the earth's surface.

The air is becoming more dense as it sinks, and any water is vaporized into the air mass. There is no water to form clouds and the air is stable, fair, and dry. A cold air mass will rotate in an anti-cyclone, or clockwise in the northern hemisphere counter-clockwise in the south. High pressure systems are settled, are usually larger than lows, and they last longer, into days or weeks.

Based in San Diego, John Brennan has been writing about science and the environment since How to Read a Water Barometer. How Does a Cyclone Affect the Weather? Wind Speed Vs. Air Pressure. What Are the Doldrums? How Landforms Affect Weather. So what does this have to do with high and low pressure?

Well, high pressure is associated with sinking air, and low pressure is associated with rising air. But why? The answer has to do with the typical air flow around high and low pressure.