Wind Speed and Air Pressure

We all have experienced a windy day, as it rushes through, you might have wondered how does it flow? Well, the answer is pressure. Yea, it may not be intuitively obvious that they are related - wind and pressure - but wind can flow only because of the pressure gradient.

The study of the atmosphere (meteorology) indicates that the movement of air is from high pressure to low pressure. This pressure difference is caused by temperature changes. This air pressure is different at different locations and that results in the flow of air which is called wind. Wind is air pressure transformed into movement of air.

Wind Speed and Air Pressure

The atmosphere of earth is composed of layers of gases, it is commonly called air. The air exerts a certain amount of pressure, the pressure (hydrostatic pressure) is due to the weight of the air above a certain point. On the surface of the earth, it is called surface pressure and is directly proportional to the mass of air present over that location. Pressure gradient pushes air from high pressure to low pressure and wind flows. The speeding wind has kinetic energy. That energy is converted into static atmospheric pressure as the wind slows down and the air accumulates at a place.

Thus, high wind speed is accompanied by reduced air pressure. The wind speed is determined by the difference of pressure at two points. An extreme low pressure at any point will cause very high wind speed. High speed winds and air pressure differences can cause severe storms. At high temperatures, the hot air becomes less dense and gets lighter, it rises up from the earth’s surface, leaving a vacuum on the surface. When the mass of air is suddenly reduced at one point due to temperature fluctuation, there is a drop in air pressure. Air accumulated at some other point, then rushes to fill the space, to even out the variation. This results in a wind flow.

As the wind blows from one place to another, the earth’s rotation affects its direction. In the northern hemisphere, winds curve rightward (i.e., wind blows clockwise around an area of high pressure) due to the spin of the earth, whereas in the southern hemisphere, the wind curves leftward and wind blows counter-clockwise around high pressure. This is called the Coriolis effect.

High Speed Wind

Wind speed is affected by local weather phenomena, low-pressure conditions can give rise to freak weather conditions and cause high velocity of wind that may result in the formation of cyclones, hurricanes, and tornadoes.

A cyclone is formed when a large mass of wind starts rotating around an extremely low-pressure centre. In the Atlantic Ocean and parts of the Pacific Ocean (North-eastern), cyclones are referred to as ‘Hurricanes’, and in the Pacific Ocean (North-western), it is called ‘Typhoon’.

A Tornado is a column of air rotating violently extending from the ground to the cloud. Tornadoes usually hang or form below cumuliform clouds. The vortex of wind is mainly referred to as Tornado.

High speed winds have tremendous energy. It can uproot trees and blow roofs. Climate change causes abnormal weather conditions resulting in such extreme phenomena resulting in loss of life and property.

Air Pressure Examples in Daily Life

• Blowing a balloon. As air is blown into a balloon, the air pressure inside it causes it to expand.

• Air pressure keeps the bicycle tyre inflated.

• Air pressure developed inside a pressure cooker causes it to whistle.

Interesting Facts

• Wind speed is measured using a tool called Anemometer. It is a device with a vertical pillar and three to four cups (caved inward). Horizontal flow of air is measured by the anemometer.

• Barometer is the instrument used to measure air pressure at a point.

• The fastest wind speed recorded ever in history is 408km/hr. It was from a hurricane gust, on 10th April, 1994 when a Tropical cyclone named Olivia (a hurricane) passed by Australia’s Barrow Island.

• Winds are given different terms based on their speed. Wind speed is classified by the Beaufort scale.

Key Feature

• The weight of the air above a certain location exerts pressure.

• The wind blows from high pressure to low pressure.

• The movement of air due to pressure difference is called wind.

• As air flows away from one point, the air pressure drops.

• High speed winds are accompanied by reduced air pressure.

Summary

Earth's atmosphere is made up of a mixture of gases which we call air, the mass of air exerts pressure upon the earth’s surface. Wind flows due to the difference in air pressure; it flows from a region with high-pressure to a low-pressure region. The larger the pressure difference, the higher the speed of the wind. Strong winds are accompanied by high pressure causing storm-like situations.