An easy to understand model of the earth's surface wind system or overall wind circulation is depicted in fig. The real wind system is significantly more intricate than the one portrayed in the model since the earth's surface is assumed to be uniform in this model, which implies that either all or all of the water and the impacts of local systems have been neglected.
It should be emphasised that wind is produced by pressure gradients caused by uneven heating of the earth's surface. There are three latitudinal circulations, and each hemisphere experiences significant longitudinal fluctuations.
1. Trade winds:
The equatorial region has the highest heating and expansion, which causes air to rise and create the doldrums, an area of low pressure (50°N to 50°S latitude), or equatorial low or calm. The sub-tropical high, often referred to as the Horse latitude belt, is caused by rising air from the equator and has a pressure range of 350 N to 350 S. As a result, the winds originate from the horse latitude belt. As a result, "Trade winds" are the winds that blow from horse latitude to the equator. Corollas force causes these winds to be redirected to the right in the northern and southern hemispheres and to the left in the southern hemisphere, where they become the north-east trades and south-east trades, respectively.
Hadley cell refers to the blow of air from the equator and buildup of air over 25–35 0 latitudes that causes a high pressure belt of descending air.
2. Westerlies wind:
There situated at about 600 – 650 latitudes a low pressure area in both the hemisphere is known as sub-polar low or polar front. The winds that flow from sub-tropical high pressure area (Located at 250 – 350 latitude in both the hemisphere ) to the low pressure area, situated at about 600 – 650 latitude in both the hemisphere, are known as Westerlies or prevailing wisterias ( anti trade winds) In the upper atmosphere the reverse air movement takes place. This circulation is known as feral cell. These winds instead flowing in straight line are deflected due to corollas force. In northern hemisphere their direction is North – West and in southern hemisphere it is South-West.
3. Polar winds or Polar Easterlies winds :
There is constant high pressure on the poles because to air contraction near the poles and cooling. Thus, winds blow from the polar high to the subpolar low pressure region, which is located between 60 and 650 latitude. In the northern and southern hemispheres, respectively, the wind blows from northeast to southeast. Clod air makes up these winds. Polar cell is the term used to describe the airflow.
Local Winds:
These winds are referred to as local winds since they are produced as a result of local conditions and have a very limited impact.
1. Land and sea breeze :
The term "land and sea breezes" refers to the movement of air caused by uneven heating and cooling between the sea and the coastal land. They are of a regional nature. the sea and land winds along the shore during the day. They are of a regional nature. Low pressure over the land is caused by the coastal land heating up more quickly throughout the day than the surrounding sea. As a result, the surface air flows from the sea to the land and is referred to as sea breeze. While at night the land cools more quickly than the water, generating a higher pressure area over land than the sea. As a result, air blows from land to sea and is referred to as land breeze.
2. Mountain and valley breeze:
Mountain and valley wind is the movement of air between two locations that occurs as a result of uneven heating and cooling. The valley wind during the day. The valley bottoms warm up more throughout the day, and the air above it rises and expands. Valley breeze is the term for this ascending air that flows up the mountainside. The procedure is reversed at night. The valley's air constricts as a result of cooling, and air from nearby hills and mountains fills the gap. Mountain breeze is the term for the chilly air that descends into the valley from the mountain ranges.
3. Ketabatic winds:
During the winter, a mass of cold air above an elevation plateau tends to thicken due to radioactive cooling before dissipating into the valleys below. Ketabatic winds are the down slope, drainage-type winds that develop. Most winds are rather light, seldom topping 4 to 5 m/s. However, on occasion, a moving cyclone or anticyclone may stir up the cold, thick air, causing the Ketabatic winds to become violent and devastating.
