Strong winds are one of the main characteristics of a hurricane. But what exactly is wind? Wind is simply air in motion relative to the Earth’s surface. Although we normally think of air moving horizontally, it can actually move in all three dimensions. Wind speed indicated the rate of this motion relative to a unit of time and is usually measured in miles per hour (mph).
The surface maps you see on weather channels will often show H’s and L’s in various locations. The H’s and L’s represent high and low pressure systems, respectively. The lines surrounding these H’s and L’s are called isobars, which are lines of constant pressure. The closer the isobars, the faster the rate of pressure change over a given distance.
Wind blows in a clockwise direction around high-pressure systems, and counterclockwise around low-pressure systems. This is true only in the Northern Hemisphere, and the opposite applies in the Southern Hemisphere.
The next question to ask is: why does wind blow? According to literature, there are three forces that cause wind to blow in the direction that it does: pressure gradient force, Coriolis force and friction. The pressure gradient force takes place due to different pressures in the atmosphere. In an attempt to level out this pressure, air flows from high pressure to low pressure.
The Coriolis force is a bit trickier to understand, but is basically caused by the earth’s rotation. This force causes moving objects like the air, a baseball or a plane, to deflect to the right of their motion in the Northern Hemisphere, and to the left in the Southern Hemisphere. The Coriolis force is strongest near the poles and zero at the equator.
Friction is the third force acting on wind. This force becomes most important near the Earth’s surface because the surface of the Earth is rough. Friction causes air to slow down and then interact with pressure systems. Air can spiral into a low-pressure system and converge into it. This will cause the air to rise up, and then possibly condense and form clouds and precipitation. It is for this reason, that low-pressure systems are associated with bad weather conditions.
Alternatively, if air spirals out of a high-pressure system, then the air higher up has to sink to replace the air that is moving away from the system. When air sinks it tends to warm and evaporate clouds in the atmosphere.
A wind can be describes as a quiet breeze or a sudden gust. It can propel sailing ships along their journey, or destroy trees and tear of roofs. Wind can also shape landforms and move entire deserts across great distances. Today, wind is increasingly being used to generate renewable energy for our power grid. In short, wind is a power force of nature that can be both a friend and a foe.
