KERALA PSC / PHYSICAL GEOGRAPHY / WINDS / NOTES /
OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE
KERALA PSC / PHYSICAL GEOGRAPHY / WINDS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE
·
A
wind can be defined as a stream of air in a fairly well-defined direction.
Winds are generated due to differences in pressure from one place to the other.
·
Wind
is ‘air in motion’ and plays an important role in climatic variations on the
earth
·
Air
always moves from a region of high pressure to a region of low pressure
·
The
Auroras are the rolling lights in the atmosphere which are visible in the high
latitude regions.
·
It
is called Aurora Borealis in the Artic Zone and Aurora Australis in the
Antartic zone.
·
Albedo is the percentage of radiant energy reflected back by
the surface
·
The
winds blowing in the Northern Hemisphere are deflected to their right and those
blowing in the Southern hemisphere to their left under the Coriollis effect.
This principle of deflection is called Ferrel’s Law. Ferrel’s law is a law
postulated in 1856 by the American scientist William Ferrel
·
Planetary
winds are permanent
winds which blow throughout the year from one latitude to the other in response
to the latitudinal differences in air pressure. They blow over the vast areas
of continents and oceans. Eg: trade winds and westerlies and polar winds
·
Trade
winds refers to the
winds that blows from the sub-tropical belts of high pressure towards the
equatorial region of low pressure.
·
Trade
winds blow towards the equator between 5º and 30ºnorth and south latitude
·
The
word ‘trade’ comes from the saxon word ‘tredon’ which means ‘to tread and
follow a regular path.’
·
Trade
winds are also called tropical easterlies
·
Trade
winds are called so because prior to the steamage; sailing ships carrying goods
of trade and cargo depended on these winds.
·
Doldrums are equatorial belts of low pressure where the north-east
and south-east trade winds converge on and meet each other approximately
between 5º south and 5º north latitude. The belt is characterized by extremely
low pressure with calm conditions
·
Westerlies
or Anti-Trade winds
are regular winds which blows outside the tropics in the temperate zone. These
winds blow from the sub-tropical high pressure areas to sub-polar low pressure
areas and between 35º and 60º North and South latitudes
·
Roaring
Forties are powerful
westerly winds that blow throughout the year over the oceans of the southern
hemisphere between 40º and 60º south latitudes. They are called Best brave
winds and bring storms and heavy rainfall.
·
The
winds which developed between 45º and 55º are called Furious Fifties and
that developed between 55º and 65º are called Shrieking sixties. These
are the dreaded terms used by sailors.
·
Polar
Easterlies constitute the
wind system characteristic of the arctic and polar zones. They extend from
about 60º north and 60º south latitude to the poles.
·
Secondary
or Periodic Winds:
The winds that change their direction periodically with the change in season,
are called secondary or periodic winds. Eg: Monsoon winds
·
Monsoon
winds are seasonal
winds which blow briefly over India, Sri Lanka, China and North West Australia
·
Monsoon
climate is marked by summer rains and winter droughts
·
The
word ‘monsoon’ derived its name from the Arabic word ‘mausin’ meaning seasonal
winds. Traditionally monsoon has been considered as a result of the differential
heating of land and sea
·
According
to dynamic theory, monsoon are a result of the shift of the Inter Tropical
Convergence Zone (ITCZ) under the influence of the vertical sun.
·
Horse
Latitudes are sub-tropical belts of variable winds and columns that lie between
the latitudes of 25º and 35º North and South. They coincide with the
sub-tropical high pressure belts.
·
Horse
Latitude winds are weak and shifting. In early days, the sailing vessels with a
cargo of horses found it difficult to sail under such calm conditions. They
used to throw horses into the sea to save valuable drinking water and this part
therefore came to be called as Horse Latitudes.
·
Local
winds develop as a
result of the local differences in temperature and pressure. They affect the
smaller areas and are restricted to the lowest levels of the troposphere.
·
Local
winds include hot, cold, convectional and slope winds
·
The
most famous local cold winds that blow from Alps over France towards the
Mediterranean sea is the mistral.
·
Loos are very hot and dry local winds that blows from the
west in the months of May and June, usually in afternoons in the plains of
Northern India and Pakistan. Its temperature invariably varies between 45ºC and
50ºC. It may cause sun stroke to people.
·
Foehn
is a hot wind of
local importance in the Alps. It is a strong, gusty, dry and warm wind. It
develops on the leeward side of a mountain range. Due to regional pressure
gradient stable air is forced to ascend the windward side causing precipitation
on the mountains.
·
Chinook is a local wind that moves down the Rockies. The word
‘chinook’ literary means ‘snow eater’. It keeps the grasslands clear from snow
during much of the winter.
·
Local
convectional winds are of two types – Land breeze and sea breeze
·
Land
breeze is defined as the
process by which cold winds blows from the land to sea during night. Land breeze
is not as strong as the sea breeze.
·
During
the day time, the land get warmer than the sea producing low pressure over the
land into which cooler air moves from over the sea. The local winds that blows
from sea to land during the day time is called Sea breeze
·
Valley
breeze and mountain breeze are the counterparts of land and sea breeze. During
the day time the slopes of the mountain gets heated more than the valley floor.
As such the air from the valley flows up the slope. This is called the Valley
breeze. After sunset the process is reversed. Rapid loss of heat through
terrestrial radiation along the mountain slopes results in the sliding of cold
dense air from higher elevations to valleys. This is called the mountain
breeze.
·
Jet
streams are narrow
concentrated bands of meandering high velocity geotropic streams bounded by low
speed winds and is a part of upper level westerlies.
·
The
Jet streams have an average velocity of 120 km per hour in winter and 50km per
hour in summer
·
A
hurricane is a strong wind whose speed exceeds 121 km/hr
·
Cyclones
are irregular wind
movements involving closed air circulation around a low pressure centre.
Cyclones are associated with destructive and violent disturbances such as heavy
squalls and torrential rainfall.
·
Cyclones
are called hurricanes in the South-East Carribean region
·
In
the Philippines islands, Eastern China and Japan, cyclones are called Typhoons
·
Around
South-East African coast, Madagascar, Mauritius islands and north-West
Australia they are called Willie Willies
·
If
the speed of cyclone is greater than 250 km/hr, it is known as Super Cyclone
·
Tornadoes
are violently
rotating storms, characterized by a funnel shaped cloud in which winds whirl
around a small area of extremely low pressure. They are generally accompanied by
torrential rains
·
Water
Spout is a tornado occurring
in the sea usually in tropical and sub-tropical regions which connects a
whirling cone of dense cloud with a cone of spray raised from sea and thus
raises a huge column of water
·
Anti-cyclone
is a high pressure
wind blowing outwards from the centre, clockwise in the Northern Hemisphere and
anti-clockwise in the Southern Hemisphere
·
Coriolis
force is a ‘fictious’
force needed to relate the movement of air masses over the earth’s surface to
its rotating co-ordinate system (the grid). It was named after the French
mathematician Gaspard de Coriolis, who first described it in 1835
·
Coriolis
force is absent at the equator and increases towards the poles. The force is
responsible for the formation and direction of movement of anti-cyclones and
whirlpools.
KERALA PSC / PHYSICAL GEOGRAPHY / WINDS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE
