Local & Regional winds etc.

Local Winds-

1.Land and Sea Breezes-

• These types of winds are seen near the coastal area.

• It is diurnal winds. 

During The day(Sea Breeze)-

• The landmass gets heated more quickly than the adjoining sea or large lake which leads to expansion of air and air rise upward.

• This process produces a local low pressure area on land.

• But there is high pressure on surface of water or sea due to which air start moving from High pressure (water) to  Low pressure(land) Known as Sea Breeze.

• It Reaches at maximum intensity in mid-afternoon. 

During the Night(Land Breeze)-

• At night, the land and the air above it cools more quickly than the nearby water body due to which there is high pressure on land and low on water bodies which causes air to move from Land(high pressure) to Water(Low pressure )causing Land Breeze.

• It Reaches at peak shortly before the sunrise.

• In morning, fishermen enter into sea with the help of land breeze and stays there till mid afternoon. 

2.The Mountain and Valley Breezes-

During the day (Valley breeze)

• On a warm sunny day the mountain slopes are heated more than the valley floor which causes low pressure on mountain slopes and high pressure on valley floors.

• Due to which winds starts blowing from valley towards mountain slopes and its is known as Valley Breeze.

• These winds are known as Anabatic Winds.

During the Night(Mountain Breeze)

• On a cold night the mountain slopes looses heat more rapidly due to radiation loss which cools down the air surrounding to it ,thereby increasing surrounding pressure.

• Due to which winds starts blowing from valley towards mountain slopes and its is known as Valley Breeze.

• These winds are known as Katabatic winds.

Regional Winds-

There are some of the regional winds that are discussed as below-

Hot winds-

1.Loo

• During the months of May and June, a powerful and arid wind blows over the northern plains of India and Pakistan, known as the "Loo.".

• Their temperature varies between 45°C to 50°C.

• They moves from West to East direction and are usually experienced in the afternoons.

2.Foehn-

• It develops on the leeward side of the Alps mountain ranges.

• The Foehn wind is a type of local wind that is characterized by its strength, dryness, warmth, and dusty nature.

• The air is forced to ascend and cross over the barrier due to the pressure gradient in the region.

• The upward movement of air can lead to rainfall on the side of mountains facing the wind, known as the windward side, due to the cooling of the air as it rises and the subsequent condensation of water vapor.

• As the air passes over the crest of the mountain, it begins to descend on the leeward side or northern slopes of the mountain as a warm and dry wind known as Foehn winds.

• They helps in development of  pasture land  and also help the grapes to ripe early.

• The temperature of the winds vary from 15°C to 20°C which help in melting snow.

3.Chinook

• It is a warm and dry wind in North western region of North America and Canada towards rocky mountain range.

• Chinook winds occur due to the movement of warm and moist air from the Pacific Ocean towards the Rocky Mountain range in the northwestern region of North America.

Snow Eater-

• The literal meaning of chinook is ‘snow eater’ as they help in melting the snow and They keep the grasslands clearof snow.

4.Sirocco-

• It is a Mediterranean hot dry and dusty  wind that comes from the Sahara and can reach hurricane speeds in North Africa.

• Once the Sirocco wind crosses over the Mediterranean Sea, it experiences a slight cooling effect due to the moisture it picks up from the sea.

• It is most frequent in spring and normally lasts for only a few days. 

Local Names of Sirocco-

• The Leste or Leveche over Morocco and Spain.

• The Ghibli over Algeria and Tunisia.

• The Chili over Tunisia and Libya.

• The Khamsin over Egypt and the Sinai.

• The Simoon over the Mid East.

5.Harmattan-

• It is a hot and dry wind that blows over northwest Africa from the northeast and Sahara region.

• It usually carries large amounts of dust. 

Doctor wind-

• It is also known as the "doctor wind", because of its dryness compared with humid tropical air which brings releif to the local people. 

Cold Regional Winds-

1.Mistral -

• These are very cold, dry and high velocity winds.

• It originates on the Alps and move over France towards the Mediterranean Sea through the Rhone valley.

• They bring down temperature below freezing point in areas of their influence.

2.Bora-

• It is a cold, dry north-easterly wind blowing down from the mountains in the Adriatic Sea region.

• It is also caused by pressure difference between continental Europe and the Mediterranean Sea.

It is divided as follows-

light bora : It is characterized by clear sky and very less precipitation. 

Dark bora : It is characterized by gathering cloud on the hilltop which causes precipitation. 

3.Blizzard-

• It is a violent and extremely cold wind laden with dry snow.

• It blows in the Northern and Southern Polar regions like Siberia, Canada, the US.

• Wind velocity sometimes reaches 160 km/ph and temperature is as low as - 7 degree celsius. 

Different Names-

• Norther - In USA.

• Burran - In Siberia.

4.Pampero-

• It is a cold wind of South America located  in the south. of Brazil , Argentina, Uruguay, Paraguay and Bolivia. 

5.Other Local winds-

Periodic/Seasonal Winds-

Upper Air Circulation-

• Due to variation of pressure at ground and upper level of the atmosphere ,there are some winds which forms parts of upper air circulation. 

Jet Streams-

• Jet streams are high altitude, narrow air currents that flow from west to east across the planet with great force.

Introduction to Jet Streams-

Earth has four primary jet streams-

• Two polar jet streams near the north and south poles.

• Two subtropical jet streams closer to the equator. 

Discovery of Jet streams-

• In the 1920s, Wasaburo Ooishi, a Japanese meteorologist, discovered the jet stream by tracking upper-level winds using weather balloons near Mount Fuji as they ascended into the Earth's atmosphere.

• Also during World War 2 in 1944 when B-29 pilots flying toward targets in Japan discovered at their cruising altitudes winds as high as 230 mph. 

The major features of jet streams are as follows-

• These are narrow belts at the high altitude near the top of the troposphere.

• They have very high speed ranging from 120 k.m. per hour to 180 k.m per hour.

• They have high speed in Winters and less speed in Summers.

• In winter, the highest wind velocities of the jet stream are found near the east coast of Asia and weakest over the eastern Atlantic and Pacific Oceans.

• In summer, strongest jet is positioned along the Canadian border and Mediterranean region.

• Their shape is circular.

• They are several hundred kilometers wide and about 2 km to 5km deep.

• The jet stream extends up to 20° latitudes during winter and narrows down to remain confined to the poles during summer.

• The flow of jet streams is not in form of straight line. Their circulation path iswavy and meandering. These meandering winds are called Rossby waves.

• Sometimes these waves can enters into Troposphere.

• The position of the jet streams shift towards the poles during summer and towards the equator during winter due to the changing overhead position of the sun.

Index cycle of Jet Stream-

• The period of transformation of the straight path of the jet stream into wavy and meandering path is called the index cycle. 

Origin of Jet Streams-

• Jet streams are formed sue to Pressure and Temperature difference on The Earth.

• There is Thermal contrast between Polar and Tropical region due to which Pressure difference is created and these streams are formed. 

Why Jet streams have high speed in winters ?

• This is because there is high temperature difference between polar and tropical regions in winter.

• This pressure difference causes Steep Pressure gradient during winters. 

Types of Jet Stream-

Regular Jet Streams-

1.Polar Front jet stream-

• It moves from east to west in the polar cell.

• It is formed due to temperature difference between the poles and the tropical region.

• It runs at a more meandering path than the Sub Tropical Jet Stream .

• It extends between 40 and 60 latitudes in both Hemispheres.

• It occurs near tropopause between polar cell and Ferrel cell.

2.Sub-Tropical Jet Streams-

• The subtropical jet streams, also known as subtropical westerly jet streams, are fast-moving, narrow air currents located in the upper atmosphere.

• Subtropical jet streams are positioned at the tropopause between the Hadley cell and Ferrel cell.

• Its origin is related to a thermal gradient confined to the upper tropopause.

• During the summer in North India, the sub-tropical jet stream shifts northward of the Himalayas.

• In comparison to polar jet stream it is much more persistent.

• Its speed is comparatively lower than polar jet streams.

Seasonal Jet Stream-

Eastern Tropical Jet Stream-

• It forms in the upper troposphere over India and Africa in summer monsoon season only.

• It is formed due to regional reversal of the south-north temperature gradient.

• They are associated with intense heating of Tibetan Plateau during monsoon season.

• It is limited only to Northern Hemisphere.

• Its direction is opposite to that of other two jet streams I.e. in eastern direction

Stratospheric polar Jet Stream-

• These are also known as Polar Night Jet streams.

• They originate in stratosphere at an altitude of about 30 km around the poles in winter season and in summer season they becomes weak and easterly in nature. 

Significance of Jet Streams-

• When they are placed above temperate cyclones, its intensity increases.

• The bursting of monsoon in India is said to be closely related to Eastern Tropical Jet streams.

• The troughs and ridges of Rossby waves and jet streams are associated with cyclonic and anticyclonic conditions in upper air as well as on surface.

• The index cycle of jet streams results into latitudinal heat transfer between tropics and mid latitudes. 

Important One liner on Local winds, regional winds and Seasonal Winds. 

What are land and sea breezes?

They are diurnal winds seen near the coastal area.

When does sea breeze reach its maximum intensity?

It reaches at maximum intensity in mid-afternoon.

What causes the sea breeze?

The air moves from high pressure (water) to low pressure (land) due to the heating of the landmass.

What is the land breeze?

It is the movement of air from high pressure (land) to low pressure (water) at night.

When does the land breeze reach its peak?

It reaches its peak shortly before sunrise.

What are mountain and valley breezes?

They are winds caused by temperature differences between mountain slopes and valley floors.

What causes the valley breeze?

It is caused by low pressure on mountain slopes and high pressure on valley floors.

What causes the mountain breeze?

It is caused by radiation loss on the mountain slopes at night.

What are anabatic winds?

They are winds that blow up mountain slopes during the day.

What are katabatic winds?

They are winds that blow down mountain slopes at night.

What are hot winds?

They are regional winds that are hot and dry.

What is loo?

It is a powerful and arid wind that blows over the northern plains of India and Pakistan in May and June.

What is foehn?

It is a warm and dry wind that develops on the leeward side of the Alps mountain ranges.

What is chinook?

It is a warm and dry wind in North America and Canada towards rocky mountain range.

What is sirocco?

It is a hot and dry wind that comes from the Sahara and can reach hurricane speeds in North Africa.

What is harmattan?

It is a hot and dry wind that blows over northwest Africa from the northeast and Sahara region.

Why is harmattan called the "doctor wind"?

It is called the "doctor wind" because of its dryness compared with humid tropical air which brings relief to the local people.

What are cold regional winds?

They are winds that are very cold and dry.

What is mistral?

It is a cold wind originating on the Alps and moving over France towards the Mediterranean Sea.

What is blizzard?

It is a violent and extremely cold wind laden with dry snow.