In this article, we are going to discuss various important periodic and local winds flowing across the globe. This is very important as per the recent trend of competitive exams and questions are coming quite often. Students need to go through this article and mark the important points which are relevant for their exams.
Secondary or Periodic Winds
- These winds change direction as the seasons’ change.
- Monsoons are a prime example of large-scale changes in planetary wind systems.
- Other examples of intermittent winds are land and sea breezes, mountain and valley breezes, hurricanes and anticyclones, and air masses.
1. Monsoon Winds :
- Monsoons have traditionally been described as large land and sea breezes. They were therefore thought to be convective circulations on a gigantic scale. A characteristic of monsoons is the reversal of wind direction.
- In summer, the Southern Hemisphere trade winds are pulled north by the apparent northward motion of the Sun and a strong low-pressure core to the northwest of the Indian subcontinent.
- When crossing the equator, these winds are deflected to the right under the action of the Coriolis force.
- These winds are now approaching the Asian continent as the southwest monsoon. By the time it travels long distances across vast bodies of water and reaches the southwestern coast of India, the water becomes saturated with humidity, bringing heavy rainfall to India and neighboring countries.
- In winter, these conditions are reversed and a high-pressure core develops in the northern part of the Indian subcontinent. Diverging winds are created by this anticyclonic movement moving south toward the equator. This motion is amplified by the apparent southward motion of the Sun. These are the northeast or winter monsoons, which bring some rainfall along the eastern coast of India.
- Monsoon winds flow across India, Pakistan, Bangladesh, Myanmar (Burma), Sri Lanka, the Arabian Sea, the Bay of Bengal, Southeast Asia, northern Australia, and China.
- Outside of India, in East Asian countries such as China and Japan, the winter monsoon is stronger than the summer monsoon.
2. Land breeze and Sea breeze :
- Land and sea absorb and transfer heat differently. During the day, the land warms up faster than the sea. Therefore, air rises over the land, creating areas of low pressure, while the sea is relatively cool and the pressure over the ocean is relatively high.
- This creates a sea-to-land pressure gradient and the wind blows from sea to land as a sea breeze. State reversals occur at night. The land releases heat much faster than the sea and becomes cooler.
- A land breeze occurs because the difference in atmospheric pressure moves from the land to the sea.
3. Valley breeze and Mountain breeze :
- In mountainous areas during the day, the slopes heat up, air moves up the slopes, and air from the valleys blows up the valleys to fill the gaps. This kind of wind is also known as the valley breeze. At night, the slopes cool down, and the dense air flows into the valleys as mountain breezes. The cold air that flows down from high plateaus and ice fields into valleys is called katabatic wind.
- Another type of warm wind (katabatic) occurs on the leeward side of the mountains. Moisture in these winds condenses and precipitates as they cross mountain ranges. Descending the leeward side of the slope, the dry air is heated by an adiabatic process. This dry air can melt snow in a short time.
Local wind
- Differences in local temperature and pressure create local winds.
- Such winds are localized and confined to the lowest levels of the troposphere.
- Some examples of localized winds are described below.
1. Loo
- It is a harmful wind.
- The plains of northern India and Pakistan can experience very hot, dry winds from the west during most of the afternoon in May and June.
- Its temperature is always between 45°C and 50°C. It can cause sunstroke in humans.
2. Foehn
- It is a beneficial wind
- Foehn is a local hot wind flowing in the Alps. A strong, gusty, dry, warm wind occurs on the leeward side of a mountain range. On the windward side, moisture is removed from the incoming wind in the form of topographical precipitation, so the air descending on the leeward side becomes drier and warmer (katabatic winds).
- Wind temperature varies between 15°C and 20°C. The wind melts the snow to help the animals and helps the grapes ripen.
3. Chinook
- It is a beneficial wind
- Fern-like winds in the United States and Canada pull down the western slopes of the Rocky Mountains and are known as winds.
- For ranchers east of the Rocky Mountains, it is beneficial to keep prairies snow-free for most of the winter.
4. Mistral
- It is a harmful wind
- Mistral is one of the local names for the wind that blows across France from the Alps to the Mediterranean Sea. Via the Rhine Valley. Fast and very cold and dry.
- Brings a blizzard to Southern France.
5. Sirocco
- It is a harmful wind.
- Sirocco is a Mediterranean wind that blows from the Sahara and reaches hurricane speeds in North Africa and Southern Europe.
- It arises from a warm, dry tropical air mass pulled northward by a cyclone cell moving eastward in the Mediterranean Sea, with winds coming from the Arabian Desert or the Sahara. Hotter, drier continental air mixes with cooler, wetter air from an oversea cyclone, and counterclockwise circulation of low pressure pushes the mixed air over the southern coast of Europe.
- Sirocco causes dusty droughts along the northern coast of Africa, storms in the Mediterranean, and cool, wet weather in Europe.
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