Local winds simply referred to the types of wind that are caused by local factors and affect a small geographical area. Apart from the major planetary winds systems of the earth, other types of winds exist which are caused purely due to some local factors; these winds are referred to as local winds.
What are the local winds?
The term Local winds connote the winds that are peculiar to a relatively small area and are of local importance. Local winds blow over a much smaller area and change direction and speed over a shorter period than global winds.
Causes of local winds
Local winds are seasonal winds and are confined to the lowest part of the atmosphere which are caused as a result of the differences in the heating and cooling of land and sea and Gravity, including downdrafts. These local winds play a significant role in the moderation of weather and climate of a particular locality. There are different types of local winds, some good examples of local winds include the land and sea breezes, valley and the mountain breezes, Harmattan, Chinook, Fohn, etc.
Types of local winds
Some of the well-known local winds that are found in different parts of the world are described below:
- Valley and mountain breezes
- Land and sea breezes
- Foehn or Fohn
- Anabatic Winds
- Santa Ana Winds
- Katabatic Winds
- The Helm Winds
Valley and Mountain Breezes
A special type of wind movement usually takes in the mountainous regions due to the relief of the land. During the day time, the sides of the mountains turn out warmer when compared to the base of the valley. As a result, the bottom of the valley experiences high-pressure while the sides of the mountains experience low-pressure. The wind which is seen rising upwards along the slopes of the mountains during day time is called valley wind
Similarly, during night time, the slopes of the mountains get cold due to solar radiation. At this time, the valley floor remains comparatively hot. So, the cool and heavy air comes down the slopes of the mountain. The wind which during night time moves along the slope of the mountains towards the valley floor is known as the mountain breeze.
Land and Sea Breezes
These are local winds that occur daily on the sea coasts due to differences in the surface temperature of the sea and adjacent land. There is a complete reversal of wind direction of these coastal winds.
A sea breeze is a very cool moisture-laden that blows from the sea during the day toward the low pressure on the land; it is a very gentle breeze whose velocity ranges between 6-50 km per hour in the afternoon. It is important to note that the low-pressure condition on the land is due to the heating effect of the sun. During the day time, the land gets heated up more quickly than the sea. The heated air expands becomes lighter and rises thereby creating a region of low-pressure. The sea remains comparatively cooler with higher pressure, therefore the sea breeze carefully blows from the sea to replace the warm rising air on the land.
This is similar to the sea breeze, it is a cool gentle wind that blows towards the sea from the land during the night. However, the reverse of the sea breeze takes place at night. This is rapidly heated up in the day time and at night cools more rapidly than the sea so that cold and heavy air is formed thus giving rise to a high-pressure condition over the land and a low-pressure region is created on the sea.
However, the land and sea breeze systems are very shallow with an average depth of 1-2 km. Over lakes, the height of circulation is much less. Warm tropical areas, where intense solar heating persists throughout the year, experience stronger and regular breezes compared to higher latitudes.
The name monsoon is derived from the Arabic word mausim, which is interpreted as a season (most of the rain that falls in Southeast Asia occurs during the summer). One can tell where the monsoons originate since winds are always defined by the direction from which they are coming; so the southwest monsoons start in the southwest and move towards the northeast, etc. In summer the intense heating of the Asian continent causes air to rise, which lowers the air pressure and consequently sucks in air from the southern hemisphere, causing winds from the south to cross over the equator. This creates the opposite effect of the Coriolis force in the northern hemisphere, causing it to change direction by over 900, resulting in the southwest monsoons. These winds are not just warm, but they have also traveled a long distance over the Indian and Pacific Oceans, and as a result, are full of moisture. When these winds pass over the land, they are forced to rise, which causes them to cool and give up their moisture in the form of torrential rain.
Harmattan is a strong dry northeast trade wind that blows from the Sahara desert high-pressure area towards the North-West African coast, it usually starts from November to mid-March. It is relatively cool, dry, and dust-laden and full of fine desert dust which makes the atmosphere hazy and dusty making aircraft operations and river navigation difficult. This affects the temperature as well as humidity so that the hot, humid climate of West Africa is set free. Hence, the harmattan is affectionately called Doctor.
It provides a welcome relief from the moist heat and is beneficial to the health of people in so many ways. When this wind occurs, there is usually an increase in evaporation and is beneficial to farmers to dry crops like beans, coffee, and corn. Its prolonged dry and dusty condition in most cases is injurious to human health, for instance, the excess drying of moisture from the atmosphere causes the skin to crack and nosebleeds to some people. Severe damage to crops especially in the hinterland where such crops wither away is a common experience. The interaction of the Harmattan with monsoon winds can cause tornadoes and also increase fire risk.
The term is associated with the strong, dusty, dry, and warm wind that blows from the alps mountain ranges during the winter season due to local differential heating which results in pressure difference on both sides of alps. The wind follows the relief line uphill thereby cooling adiabatically and this results in rainfall on the windward side.
Thick clouds usually characterize the windward side. As the wind descends the leeward side, they are virtually dry, and a fantastic increase of over 160 to 200 C has been recorded on various sides of the Alps mountain ranges. Foehn wind is a warm, dry wind that absorbs moisture rather than resulting in rainfall.
The high temperature, however, helps snow at the mountain top to thaw and this often leads to the destruction of life and property and sometimes, the destruction of the communication line. Foehn winds help farmers as they help to melt the ice, leading to the early ripening of grapes and growth of grass which the animals feed on.
The Chinook winds just like the Fohn wind are warm dry westerly winds that blow down the eastern slope of the Rockies into the heart of the United States of America and Canada. The literal meaning of Chinook is now eater as they help in melting the snow earlier. The winds are cool and deposit moisture on the windward side of the Rockies.
On the leeward side of the Rockies, it warms adiabatically and becomes more capable of raising the temperature of the regions by as much as 120C in few minutes. before the arrival of Chinook, the wind hardly reaches 60C. It is usually below the freezing point, animals are strictly kept indoors and crops and vegetables are grown in greenhouses, but the arrival of Chinook reactivates life as the temperature moves from negative to a positive degree (above freezing). The winds keep the grasslands clear of snow. Hence, they are very helpful to ranchers.
Sirocco is a hot, dry, and dusty wind, that originates in the Sahara desert. It frequently occurs in spring and normally lasts for only a few days. After crossing the Mediterranean sea, the Sirocco is slightly cooled by the moisture from the sea. Still, it is harmful for vegetation, crops in that region. It is known by different names in different regions such as Leveche in Spain, Gharbi in the Aegean Sea area, Khamsin in Egypt.
Loo is a hot and dry wind, which blows so heavily over the northern plains of India and Pakistan usually from the month of May and June. They blow from west to east direction as they occur mostly in the afternoons. Their temperature varies between 45oC to 50oC.
This wind starts on the Alps and moves over to France towards the Mediterranean Sea through the Rhone valley. Mistrals are characterized by very cold, dry, and high velocity. They reduced the temperature below freezing point in areas where they take place. As a protective measure, many people in this area plants thick rows of trees and hedges to shield their crops and houses from the Mistral.
Bora is a cold dry north-easterly wind blowing down from the mountains in the Adriatic Sea region. It is also caused by the pressure difference between continental Europe and the Mediterranean Sea. This wind usually takes place in winter and most times reaches a speed of over 150 km/h.
This is a violent and extremely cold wind laden with dry snow. This kind of wind is very common in the Antarctic regions. Wind velocity sometimes reaches 160 km/h and the temperature is as low as -70 C.
This is a very strong wind that blows in Argentina and Uruguay, specifically in the Rio de la Plata area during the month of June to September The wind is marked with cold fronts and it usually starts with rain, lightning, and thunder. When this occurs, there is usually a rapid drop in temperature and a sudden change of wind direction from northerly or northwesterly to southerly or south-westerly.
This is a strong, dry, desert wind that blows in the Sahara, Israel, Jordan, Syria, and the desert of Arabia.
Southerly is the name of a storm or front of air originating from the south. In Wellington, New Zealand these storms are usually short and frequently have winds gusting between 120 km/h and 160 km/h through higher speeds are known. These winds are known by different names in Sydney and Melbourne, while in Australia, they are known as southerly busters.
Anabatic winds are the type of winds caused by thermal (heat) processes. The winds occur over slopes that are being heated by the sun. Once the air comes in contact with warmed slopes, they expand upward and cool and sinks over valleys of the neighboring surrounding. Anabatic winds are said to be slow, at only 1-2 m/ second, they occur sometimes near the coasts where they can increase the strength of sea breezes.
Santa Ana winds
These are strong and very dry down-slope winds which blow mostly in the Autumn and winter, it starts from the inland and affects the northern Baja California and coastal Southern California. They are known especially for the hot dry weather often the hottest of the year that brings along the fall and is really famous for bringing along with them wildfires in regions where they occur. However, they are popularly called devil winds across Southern California.
The Katabatic or down-slope winds usually occur over slopes that are cooled. Katabatic winds occur where the air in contact with the sloping ground is colder than air at the same level away from the hillside over the valley. Katabatic winds are nocturnal phenomena in most parts of the world (which means they mostly take place during the night hours as there is surface cooling.
The Helm Wind
It is an easterly wind that originates in Cumbria, North England, where the winds blow over Cross Fell and then descend into the Eden Valley. A bank of cloud is usually formed at the hilltops, and the roaring of the wind can be heard from a very far distance.
Importance of local winds.
- Local winds have very important effects on the weather and climate of some regions as they help to moderate the climate of nearby areas with sudden increase or decrease in the temperature and humidity, but this moderating effect completely depends on the location of the place.
- Local winds allow the circulation of air, enabling us to breathe in oxygen.
- They are important forces that produce waves, the wind energy can be used to harness powerful turbines.
- The wind is an important renewable resource that does not directly cause pollution
- Local winds allow rain to get over mountains, as this wind approaches the mountain, it brings moisture with it, which condenses as rain and other precipitation before coming over the base of the mountain.
- They also help transport seeds, pollen grains, sand or dust from one place to another
- Winds also help drive ocean surface currents around the world. An example of this is the Antarctic Circumpolar Current which transports nutrient-rich water and cold around Antarctica.