Trade Winds: Classification, Derivation & Direction

Trade winds can be defined as the wind that flows towards the equator from the north-east in the Northern Hemisphere or from the south-east in the Southern Hemisphere. These are also known as tropical easterlies and are known for their consistency in force and direction.

• Trade winds form when the hot air rises, hitting the equator where it moves towards the poles, making them cold in nature.
• They flow from the subtropical zones with higher air pressure to the equatorial zones with comparatively lower air pressure. This phenomenon is governed by Ferrel’s Law as well as Coriolis Effect
• In meteorology, Trade winds go about as the directing stream for typhoons that structure over the Atlantic, Pacific, and southern Indian Oceans. 

Also read: Pressure

Key Terms: Trade Winds, Types of winds, Planetary Winds, Latitude, Altitude, Coriolis Effect, Ferrel’s Law, Easterlies

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What are Trade Winds?

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Trade winds or easterlies are the type of winds which flow towards the equator from the north-east in case of the Northern Hemisphere, or from the south-east in case of the Southern hemisphere.

• These winds generally form when the hot air is seen to rise, which then hits the equator wherein it moves towards the poles, making it cold.
• These type of winds are used usually by sailors. 
• In fact, the sailors who travelled from Europe were known to use trade winds in order to travel to North or South America.
• Trade winds are stronger and consistent over the oceans than over land, forming partly cloudy sky conditions which are characterized by shallow cumulus clouds.

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Classification of Winds

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There are many basis for the classification of wind. Following are the most prominent classifications of winds: 

Planetary winds

Planetary winds are also often known by the name of prevailing winds and occur due to the difference in air pressure from one latitude to another.

Westerlies

Westerlies migrate at midlatitudes between 30° and 60° latitude, from the west to the east. 

• Westerlies usually form between 40 degrees and 65 degrees S latitudes.
• In both the northern and southern hemispheres, they primarily originate in the southwest and northwest, respectively. 
• They are also referred to as the Furious Fifties and Shrieking Sixties. 
• They resemble the tradewinds since they both blow in the northern and southern hemispheres. 
• Westerlies are responsible for the wind patterns in the U.S and Canada.

Polar Easterlies

The polar easterlies originate from high-pressure areas in the polar zones. 

• These are characterized by dry, cold, and year-round winds that flow from the north of the northern hemisphere and the south of the southern hemisphere towards the north direction. 
• The polar easterlies occur between 60°and 90° in the latitude in both the northern and southern hemispheres. 
• They impact the sail of ships and hence are crucial for the sailors. 
• The direction is majorly impacted by the Coriolis Effect. 

Monsoon Winds

These winds flow in areas of low altitude and are known to alter the directions of their flow between summers and winters. 

• Monsoon winds flow from land to water in winter and from water to land in summer. 
• They influence the precipitation and temperature patterns of the region. 

Land Breeze and Sea Breeze

Local wind patterns known as “land breezes”are characterized by dry winds that blow from land to sea. 

• These winds are pleasant and dry. 
• Sea breezes, however, are winds that originate from the sea and travel inland while carrying some moisture. 

Valley and Mountain Breeze

Mountain slopes become heated throughout the day, and air rushes upslope to fill the resulting gap, creating a valley breeze. At night, the dense air pours into the valley as a mountain breeze as the mountain slopes cool.

Local Winds

Local winds are a result of pressure and temperature changes. Such winds only occur in the lowest troposphere levels. Some common examples of local winds are Zonda, Loo, and Bora.

Periodic Winds

Periodic winds usually depend on the seasons, and are known to change their direction as per the Monsoons.

Also Check: 

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What is Coriolis Effect?

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The Coriolis effect is a hypothetical or inertial force that causes winds to be deflected to the right in the northern hemisphere and to the left in the southern hemisphere. 

• Coriolis Effect is used to derive Ferrel’s Law. 
• In the Northern and Southern hemispheres, moving objects tend to diverge towards the right and left, respectively. 
• This phenomenon that is naturally occurring and causes alterations in wind directions is called Coriolis Effect.
• The Coriolis effect is not observed underneath a horizontally traveling object near the equator since there is no rotation of the earth's surface (a sensation of turning).

Also Read: Types of Wind

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Derivation of Coriolis Effect using Ferrel’s Law

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The mathematical description of the Coriolis Effect using Ferrel’s law is as follows:

Where, 

• m = mass of the object
• a = acceleration of the object (relative to the inertial reference frame)
• F = sum of all vector physical forces applying to the object

To create a non-inertial reference frame for the equation as mentioned above:

Where,

• Ω = rotational vector
• r = position vector of the object
• v = Velocity relative to the rotating reference frame
• a = acceleration relative to the rotating reference frame

 Also read: Equations of Motion

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Direction of Trade Winds

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The revolution of the earth on its axis, alongside other factors, contribute to the trade winds which blow westward. When the cooler air near to the poles move downwards, a warm, humid air is seen to rise from the equator, thus producing trade winds.

• With the earth rotating as the air flows, the northern hemisphere winds move to the right, while leftwards in the southern hemisphere.
• This phenomenon of natural wind is also known by the name of Coriolis effect.
• Due to this effect, the trade winds in both the northern and southern hemispheres move toward the west. 
• Trade winds can be found between 300 north and south of the equator. 
• The region close to the equator (also known as the doldrums) has no wind.

Weather and Biodiversity effect of Trade Winds

Clouds that can be found within trade wind systems are composed of cumulus. They typically expand around 4 kilometers (13,000 ft) in height. 

Trade winds begin from the poles (north-east in the Northern Hemisphere, southeast in the Southern Hemisphere) in the Winters. 

Trade winds are known to be stronger in the colder time of the year than the late spring. Trade winds are stronger in case of forests.

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Things to Remember

• The trade winds are a set of prevailing winds which blow from east to west across the tropical regions of the Earth.
• Winds can be classified into Easterlies, Westerlies, Land and Sea Breeze, Monsoon Winds, Mountain and Valley Breeze, Periodic Winds, etc. 
• During Winters, trade winds intensify, blowing from the southeast in the southern hemisphere and from the northeast in the northern hemisphere.
• In mathematical terms, Coriolis Effect using Ferrel’s law can be represented by F = ma.
• The Coriolis Effect is a natural phenomenon influencing the origin and direction of the flow of trade winds.

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