Wind: An Overview
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.
FAQs on Wind Speed and Air Pressure
1. What is the fundamental relationship between wind speed and air pressure?
High wind speed is accompanied by reduced air pressure, while low wind speed is associated with high air pressure. Air always moves from an area of high pressure to an area of low pressure, and this movement of air is what we define as wind. The greater the difference in pressure between two locations, the faster the wind will blow.
2. How does temperature difference cause wind to blow?
When a region of the Earth gets heated by the sun, the air above it also becomes hot. Hot air expands, becomes less dense, and rises, creating an area of low pressure. Cooler, denser air from surrounding areas, which is at a higher pressure, then moves in to fill this space. This movement of air from a high-pressure region to a low-pressure region is what causes wind.
3. Why does blowing over a strip of paper make it rise?
This is a practical example of the relationship between air speed and pressure. When you blow over the top surface of the paper, you increase the speed of the air in that area. Faster-moving air exerts lower pressure. The air underneath the paper is still and remains at a higher pressure. This pressure difference creates an upward force, known as lift, that pushes the paper upwards.
4. What are some real-world examples of high-speed winds being caused by air pressure differences?
Extreme weather events are powerful demonstrations of this principle. Key examples include:
- Cyclones and Hurricanes: These are large, rotating storm systems that form around a central area of extremely low air pressure. Air from surrounding high-pressure regions rushes towards this low-pressure centre, creating very high-speed winds.
- Tornadoes: These are violently rotating columns of air where a sudden and significant drop in air pressure creates incredibly fast and destructive winds extending from a thunderstorm to the ground.
5. Why does air pressure decrease as you go to a higher altitude?
Air pressure is essentially the weight of the column of air above a certain point. As you ascend to a higher altitude, for example, when climbing a mountain, the amount of air above you decreases. With less air pushing down from above, the weight is lower, and consequently, the air pressure is lower. This is why the air is described as being 'thinner' at high altitudes.
6. How are high wind speeds and low air pressure related in a cyclone?
In a cyclone, a core area of very warm, moist air rises rapidly. This rapid upward movement creates a zone of extremely low atmospheric pressure at the ocean's surface, forming the 'eye' of the storm. The surrounding air, being at a much higher pressure, is forcefully drawn towards this low-pressure centre. The Earth's rotation causes this in-rushing air to spiral, generating the characteristic high-speed rotating winds of the cyclone.
7. What instruments are used to measure wind speed and air pressure?
Specific scientific instruments are used to measure these two distinct but related weather variables:
- Wind speed is measured using a device called an anemometer.
- Air pressure, also known as atmospheric pressure, is measured using an instrument called a barometer.
