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QuickReview :: Geography #1
Notes
The Sun
accounts for 99.85% of the mass of the Solar System
is 150 million km from the Earth
has a diameter of 1.4 million km
is 5 billion years old
is expected to die in another 5 billion years
temperature at the core: 15 million K
temperature at the surface: 5700 K
chemical composition: Hydrogen 82%, He lium18%, Oxygen 0.03%
Cosmic yearis the time taken by the Sun to complete one revolution around the center of thegalaxy. It is taken to be 250 million years.
Red Giantis a star that has completely burnt out its resources of Hydrogen. The star then loses
its luminous intensity and turn red in colour. The Sun is expected to become a Red Giant inabout 5 billion years.
Sunspotsare regions on the surface of the Sun that are cooler (1500 C) relative to the normal
temperature (6000 C). Sunspots cause magnetic interference on the Earth, thereby resulting in
interruptions to satellite and radio communication.
Questions
1. One AU is the average distance between1. the Earth and the Sun
2. the Earth and the Moon
3. Jupiter and the Sun
4. Pluto and the Sun2. Consider the following statements
a. Asteroids are rock debris of varying size orbiting the Sun
b. Most asteroids are small but some have diameters over 1000 km
c. The orbit of asteroids lies between orbits of Jupiter and Saturn
Which of the above are correct?
4. a, b and c
5. b and c6. a and b
7. a and c
Solar eclipse achieves totality only in limited geographical regions because
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0. the shadow of the Moon on the Earth is small compared to the cross section of the
Earth
1. the Earth is not a smooth flat surface, but instead has elevations and depressions2. the trajectory of the Moon around the Earth and the Earth around the Sun are not
perfect circles
3.
the Suns rays reach most peripheral regions of the shadow of the Moon due torefractionThe limit of mass beyond which stars suffer internal collapse is called the
0. Chandrasekhar limit
1. Eddington limit2. Hoyle limit
3. Fowler limit
Geography #2 | Study Material :: General Studies | IAS Help
COMPOSITION OF THE SOLAR SYSTEM
THE PLANETS
1.
Mercury
1.
Closest planet to the Sun
2.
Smallest planet
3.
No satellites
2.
Venus1.
Very dense atmosphere
2.
Hottest planet (over 400 C)
3.
Large amount of greenhouse gases
3.
Earth
1.
Hydrosphere unique among rock-based planets
2.
Only planet where plate tectonics observed
4.
Mars
1.
Atmosphere made mainly of carbon dioxide
2.
Red colour comes from iron oxide
3.
Geological activity such as volcanoes as recently as 2 million years ago
5.
Jupiter1.
2.5 times the masses of all other planets combined
2.
Composed mainly of hydrogen and helium
3. Great Red Spot in atmosphere created by strong internal heat
4.
63 known satellites. Ganymede, Callisto, Io and Europa show similarities to terrestrial
planets such as volcanism and internal heating
5.
Ganymede is the largest satellite in the solar system. It is larger than mercury
6.
Has planetary ring system
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6.
Saturn
1.
Extensive ring system
2.
Rings made by small particles of water ice clumped together
3.
Rings first observed by Galileo
4.
Least dense planet in solar system
5.
60 satellites
6.
Titan is the only satellite in the solar system with a substantial atmosphere
7. Uranus
1. Orbits the sun on its side
2.
Very cold core, radiates little heat
3.
27 satellites
4.
Has planetary ring system
8.
Neptune
1.
Smaller in size but more massive and more dense than Neptune
2.
13 known satellites
3.
Has planetary ring system
OTHER COMPONENTS
1.
Asteroids
1.
Small objects composed of rocky and metallic minerals
2.
Small asteroids are called meteoroids
3.
Main asteroid belt occupies orbit between Mars and Jupiter
4.
Asteroid belt is sparsely populated. Spacecraft routinely pass through belt without
incident
5. Ceres is the largest body in the asteroid belt. Classified as a dwarf planet
2. Comets
1.
Small bodies composed of volatile ices
2.
Coma of a comet (tail) is observed when proximity to the sun causes the icy particlesto sublimate and ionize
3. Hale-Bopp comet was visible to the naked eye for 18 months. It was the most widely
observed and brightest comet recorded
3.
Interplanetary medium
1.
It Is the interplanetary atmosphere created by the stream of charged particles emitted
by the Sun (called solar wind)
2.
Aka Heliosphere
3.
Stretches out to 100 AU
4.
Space weather is created by geomagnetic storms on the Suns surface which disturb the
heliosphere
5. Earths magnetic field prevents solar wind from stripping away the Earths atmosphere
4.
Kuiper belt
1.
Ring of debris, similar to asteroid belt, but composed mainly of ice
2.
Present in the area beyond Neptune
3. Pluto is the largest object in the Kuiper belt
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GALACTIC CONTEXT OF THE SOLAR SYSTEM
1.
Located in the Milky Way galaxy, a spiral galaxy. Milky Way diameter 100000 light years.
Contains about 200 billion stars
2.
Solar System resides in one of the outer arms, called Orion Arm
3.
Sun lies around 25,000 light years from galactic centre. Completes one revolution every 250million years (aka Cosmic Year)
4.
Closest star is Alpha Centauri triple star system
5.
Largest star close to Sun is Sirius
6.
Closest sun-like star is Tau Ceti
7.
Closest extra-solar planet is Epsilon Eridani b, which orbits the star.r Epsilon Eridani
IMPORTANT GEOLOGICAL FEATURES IN THE SOLAR SYSTEM
1. Venus
1.
Ishtar Terra and Aphrodite Terra: two continents on Venus
2.
Maxwell Montes: highest mountain on Venus
2.
Mars
1.
Adirondack: first rock chosen to be explored by the first Mars rover Spirit in Jan 2004
2.
Gusev Crater: crater on Mars, site of landing of the Mars rover Spirit, Jan 2004
3.
Sleepy Hollow: circular, shallow depression on Gusev crater
4.
Olympus Mons: tallest volcano and mountain in the Solar System.About 3 times as tall
as Mount Everest (88000 ft)
5.
Meridiani Planum: Landing site of second Mars rover Opportunity. May indicate the
presence hot springs or liquid water in the past
3. Moon
1.
South PoleAitken basin: largest crater on the Moon, on the far side
2. Shackleton crater: Site where the Moon Impact Probe from Chandrayaan landed and
found water, Nov 2008.Located at the South Pole, where the rim gets continuous sunlight while the interior is in
perpetual shadow.
3.
Cabeus crater: Site where the LCROSS spacecraft landed and confirmed significant
presence of water, Oct 2009.
Located at the south pole
TIMELINE OF SOLAR SYSTEM EXPLORATION
1.
1957: Sputnik 1, first Earth Orbiter
2.
1961: Vostok 1, first manned Earth orbiter
3.
1966: Luna 9, first Lunar Lander4.
1969: Apollo 11, first manned lunar landing
5.
1970: Luna 17/Lunokhod 1first Lunar Rover
6.
1971: Mars 3first Mars Lander
7.
1976: Helios 2closest Solar approach
8.
1977: Voyager 2first to leave Solar System
9.
1978: International Cometary Explorerfirst comet flyby (comets Giacobini-Zinner and Halley)
10.1996: Mars Pathfinderfirst Mars Rover
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11.
2001: Genesisfirst Solar wind sample return
TIMELINE OF SOLAR SYSTEM ASTRONOMY
1.
2137 BCE: Chinese astronomers record solar eclipse
2.
2
ND
millennium BCE: Heliocentric solar system, with Sun at the centre, proposed in the Vedictexts
3.
499 CE: Aryabhata, in hisAryabhatiya, propounds heliocentric solar system of gravitation,
elliptical orbits for planets, and suggests that moon and planets shine due to reflected light
4.
500: Aryabhata accurately computes the earths circumference, solar and lunar eclipses and
length of earths revolution around the Sun
5.
620: Brahmagupta recognizes gravity as a force of attraction and describes law of gravitation
6.
628: Brahmagupta calculates motion and position of various planets
7. 1150: Bhaskara, in the Siddhanta Shiromani, calculates longitudes and latitudes
8.
1514: Copernicus states his Heliocentric theory in Commentariolus
9.
1610: Galileo Galilee discovers Callisto, Europa, Ganymede and Io, sees Saturns rings
10.
1656: Christiaan Huygens: identifies Saturns rings as rings and discovers Titan
11.
1705: Edmund Halley predicts the periodicity of Halleys Comet
12.
1755: Immanuel Kant formulates the Nebular Hypothesis of Solar System formation
13.
1930: Clyde Tombaugh discovers Pluto
14.
1946: American launch of a camera-equipped V2 rocket provides the first images of the Earth
from space
Global Geography #3 | Study Material :: General Studies |IAS Help
STRUCTURE OF THE EARTH
Depth (in km)Layer
0-35Crust
35-60Uppermost part of the mantle
35-660
Upper Mantle
660-2890Lower mantle
2890-5150Outer core
5150-6360Inner core
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Crust
Depth varies from 70 km under mountains to 5 km under oceans
Thin oceanic crust is composed of dense iron, magnesium silicate rocks like basalt Thick continental crust is less dense, composed of sodium, potassium, aluminium silicate rocks
like granite
The boundary between crust and mantle is called Mohorovicic discontinuity.Signifies change
in seismic velocity and rock composition
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Mantle
Schematic view of the interior of Earth. 1. continental crust - 2. oceanic crust - 3. upper
mantle - 4. lower mantle - 5. outer core - 6. inner core - A: Mohorovii discontinuity - B:
Gutenberg Discontinuity - C: Lehmann discontinuity Source: Wikipedia
Thickest layer of the earth
Composed mainly silicate rocks rich in iron and magnesium
Temperature ranges from 500 C (near the crust) to 4000 C (near the core)
Despite high heat, the mantle is primarily solid due to high pressures
The mantle is slightly ductile and can flow, although only on slow, long timescales
Motion of tectonic plates is an expression of convection in the mantle
The mantle lies exposed without any crust covering on the floor of the Atlantic Ocean near the
Caribbean Islands
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Outer core
Convection in the outer core gives rise to earths magnetic field. The mechanism of the
magnetic field is explained by the Dynamo Theory, which was proposed by Joseph Larmor in1919
Liquid in composition
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Inner core
Believed to consist of an iron-nickel alloy
Hottest part of the earth. Temperature may reach that of Suns surface i.e 5700 K
Solid in composition
Compressional waves can pass through it but not shear waves
Inner core is younger than the age of the earth. Inner core: 2-4 billion years, earth: 4.5 years
Inner core is cooling slowly(about 100 C per billion years)
The inner core is too hot to hold a permanent magnetic field
It has been speculated that the inner core may rotate slightly faster than the rest of the earth
(about 0.3 to 0.5 degrees per year)
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Lithosphere
Includes the crust and uppermost parts of the mantle
Constitutes the hard and rigid outer layer of the Earth
Lithosphere is broken down into tectonic plates
Is rigid and deforms through brittle failure, causing faults
Lithosphere is thought to float or move around on the Asthenosphere, creating plate tectonics
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Asthenosphere
Lies below the lithosphere
Constitutes the weaker, hotter and deeper part of the upper mantle
Involved in plate movements Deforms viscously and accommodates strain through plastic deformation
Due to high temperature, rock becomes ductile, leading to convection currents
Boundary between Lithosphere and Asthenosphere is defined by a change in seismic velocity:
in asthenosphere seismic waves pass relatively slowly and hence it is called a low-velocity zone
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Discontinuities in the Earths structure
Discontinuity Depth Boundary Other notes
Mohorovicic
discontinuity
30-50 km
(continents)
7 km (ocean
floor)
crust-
mantle
Observed by abrupt change in seismic
wave velocity
Identified by Andrija Mohorovicic
(Croatia) in 1909
Gutenberg
discontinuity2900 km
Core-
mantle
Observed by difference in seismic
wave velocity
Lehmann
discontinuity220 km
Appears beneath continents but not
oceans
PLATE TECTONICS
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Overview
Plate tectonics is a theory that describes large scale motions of the earths lithosphere
Proposed by Harry Hess in 1962. Builds on the concepts of continental drift, proposed by Alfred
Wegener in 1915.
Tectonic plates move because lithosphere has higher strength and lower density than the
athenosphere. Thus the lithosphere rides on the athenosphere
Tectonic plates on the earth move in relation to each other
Movement of plates is typically 50100 mm annually
Earthquakes, volcanic activity, mountain building and ocean trench formation occur along
plate boundaries Plate tectonics may exist on other terrestrial planets as well, especially Mars
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Types of plate boundaries
Transform boundaries:
occur where plates slide past each other along transform faults. Eg: San Andreas Fault in
California
Divergent boundaries:occur where two plates slide apart from each other. Eg: Mid-Atlantic
Ridge, Great Rift Valley (Africa) Convergent boundaries:occur where two plates slide towards each other forming either a
subduction zone or a continental collision. Eg: Andes (South America), Japan, Himalayas
o Subduction zones:
occur where an oceanic plate is pushed underneath a continental plate. Eg ocean
trenches. The descending end of the oceanic plate melts and creates pressure on the
mantle, causing volcanoes
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o Obduction zones:
occur where the continental plate is pushed underneath the oceanic plate. However,
this is unusual as the relative densities of the plates favours subduction of the oceanic
plate
o Orogenic belts:
occur when two continental plates collide and push upward to form large mountain
ranges. Eg: Himalayas
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Examples of Divergent boundaries
East African Rift (Great Rift Valley), Africa
Mid-Atlantic Ridge: separates the North and South American plates from the Eurasian and
African plates
Gakkel Ridge: a slow spreading ridge in the Arctic Ocean
East Pacific Rise: extends from the South Pacific to the Gulf of California
Carlsberg Ridge in the eastern Indian Ocean
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Examples of Subduction zones
The oceanic Nazca plate being subducted under the continental South American Plate forming
the Chile-Peru Trench
The Pacific Plate being subducted under the Eurasian and Philippine Sea Plates forming the
Mariana Trench
The Philippine Sea Plate subducting under the Philippine Mobile Belt forming the Manila Trench
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Examples of Orogenic belts
The belt between the Indo-Australian and Eurasian Plates giving rise to the Himalayas.This is
the most dramatic Orogenic Belt in the world
Interaction between the African and Adriatic Plates with the Eurasian Plate giving rise to the
Alps
Andes belt on the western margin of South America
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Examples of Transform boundaries
The San Andreas Fault in California.This arises due to the northwards movement of the Pacific
Plate with respect to the North American Plate
Motagua Fault between the North American Plate and the Caribbean Plate
Dead Sea Transform fault which runs through the Jordan River Valley
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Major and Minor plates
Major platesMinor plates
African plateArabian plate
Antarctic plateCaribbean plate
Australian plateJuan de Fuca plate
Indian plateCocos plate
Eurasian plateNazca plate
North American plate Philippine sea plate
South American plateScotia plate
Pacific plate
Global Geography #4 | Study Material :: General Studies |
IAS Help
THE ATMOSPHERE OF EARTH
COMPOSITION OF THE ATMOSPHERE
Compound Distribution
Nitrogen 78%
Oxygen 21%
Argon 0.9%
Water vapour 0.4% (around 1% at the surface)
Carbon dioxide 0.03%
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STRUCTURE OF THE ATMOSPHERE
1. Troposphere
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1.
Begins at the surface and extends to between 7 km (at the poles) and 20 km (at the
equator)
2.
Temperature in the troposphere decreases with altitude i.e. the lowest parts are the
warmest
3.
The troposphere contains roughly 75% of the mass of the atmosphere and 99% of its
water vapour
4.
The lowest part of the troposphere, where friction with the Earths surface influences air
flow is called the planetary boundary layer. Usually extends from a few hundred metres
to about 2 km
5.
The tropopause is the boundary between the troposphere and the stratosphere
2. Stratosphere
Layers of the atmosphere
1.
Extends from the troposphere to about 51 km
2.
Temperature increases with height
3.
Restricts turbulence and mixing
4. Commercial airliners usually fly within the stratosphere (10 km) to optimize jet fuel
burn and to avoid atmospheric turbulence
5.
The stratopause is the boundary between the stratosphere and the mesosphere
3.
Mesosphere
1.
Extends from stratosphere to about 80 km
2.
Upon entering the earths atmosphere, most meteors burn up in the mesosphere
3.
Temperature decreases with height
4.
The mesopause, the end of the mesosphere, is the coldest place on Earth with an
average temperature of -100 C
4.
Thermosphere
1. Biggest layer of the atmosphere
2.
Extends from the mesosphere to about 500-1000 km
3.
Thermopause is a temperature boundary contained within the thermosphere
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4.
Temperature increases up to the thermopause, then remains constant
5.
The temperature can reach 1500 C. However, despite the high temperature one would
not feel warm because the atmospheric density is too low to enable heat transfer
6.
The International Space Station orbits in the thermosphere (320380 km)
7.
The ionosphere is formed in this layer as a result of ionization caused by ultraviolet
radiation
8.
The boundary between the thermosphere and the exosphere is called exobase
5. Exosphere
1.
Uppermost layer of the atmosphere
2.
It is a transitional zone between the Earths atmosphere and interplanetary space and
does not fully fall within the atmosphere
3.
Extends to about 190,000 km. This is half the distance to the Moon, at which the
influence of solar radiation becomes greater than the Earths gravitational pull
4.
The density is so low that molecules can travel hundreds of km without colliding with
each other
5.
Composed mainly of the lightest gases such as hydrogen and some helium
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OTHER LAYERS AND BOUNDARIES OF THE ATMOSPHERE
1.
Ozone layer
1.
It is contained within the stratosphere at about 1050 km above the Earths surface
2.
About 90% of the ozone layer is present in the stratosphere
3.
The ozone layer absorbs 93-99% of harmful ultraviolet light
4.
Ozone is formed when UV light strikes oxygen in the stratosphere to split the oxygen
atoms, which then reform as ozone
5. The ozone layer was discovered by the French physicists Charles Fabry and Henri
Buisson in 1913
6.
British meteorologist GMB Dobson established a worldwide network of ozone
monitoring stations between 1928 and 1958 that continues to operate today. He also
developed a spectrophotometer (called the Dobsonmeter) to measure stratospheric
oxygen from the ground. The Dobson unit, a measure of ozone density is named in his
honour
2.
Ionosphere
1.
Stretches from the thermosphere to the exosphere (100 km700 km)
2.
This is caused due to ionization by solar UV radiation
3. Responsible for radio propagation by reflecting radio waves back to the Earths
surface thereby enabling long-distance communication
4.
Plays an important part in atmospheric electricity (like lightning)
5.
Responsible for auroras3.
Homosphere and Heterosphere
1.
Homosphere is the part of the atmosphere where gases are well mixed due to
turbulence
2.
This includes the troposphere, stratosphere and mesosphere
3.
Heterosphere is the part of the atmosphere where gases are not well mixed
4.
This usually happens above the turbopause (100 km) where distance between particles
is large due to low density
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5.
This causes the atmosphere to stratify with heavier gases like oxygen and nitrogen
present in the lower layers and lighter gases like hydrogen and helium in the upper
layers
4.
Planetary boundary layer
1.
Part of the troposphere closest to the Earths surface and most influenced by it
2.
Friction with the earths surface causes turbulent diffusion
3.
Ranges from 100 m to about 2 km
5. Magnetosphere
1.
A mix of free ions and electrons from solar wind and the Earths atmosphere
2.
It is non-spherical and extends to more than 70,000 km
3.
It protects the Earth from harmful solar winds
4.
Mars is thought to have lost most of its former oceans and atmosphere to space due to
the direct impact of solar winds. Similarly Venus is thought to have lost its water due to
solar winds as well
6.
Karman line
1. Defines the boundary between the Earths atmosphere and outer space
2.
Lies at an altitude of 100 km above mean sea level
3.
At this altitude the atmosphere becomes too thin for aeronautical purposes4.
However, there is no legal demarcation between a countrys air space and outer space
7.
Van Allen Belt
1.
It is a region of energetic charged particles (plasma) around the Earth held in place by
the Earths magnetic field
2.
Extends from about 200 km to 1000 km
3.
Has important implications for space travel because it causes radiation damage to solar
cells, integrated circuits, sensors and other electronics
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PHYSICAL PROPERTIES OF THE ATMOSPHERE
1. Pressure and thickness
1.
Atmospheric pressure at sea level is 1 atmosphere (around 14.7 psi)
2.
50% of atmospheric mass is below an altitude of 5.6 km
3.
90% of atmospheric mass is below 16 km
4.
99.99% of atmospheric mass is below 100 km
2.
Density and mass
1.
Atmospheric density decreases with height
2.
Density at sea level is about 1.2 kg/cu.m
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OPTICAL PROPERTIES OF THE ATMOSPHERE
1.
Scattering
1.
When suns rays pass through the atmosphere, photons in light interact with the
atmosphere to produce scattering
2.
Eg: on overcast days there are no shadows because light reaching the surface is only
scattered, indirect radiation, with no direct radiation reaching the earth
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3.
Scattering is responsible for blue appearance of the sky, and for red appearance of
sunset
2.
Absorption
1.
The atmosphere absorbs radiation of different wavelengths, allowing only certain
ranges (UV to IR) to pass on to the earths surface
3. Emission
1.
The atmosphere absorbs and emits IR radiation
2.
Earth cools down faster on clear nights than on cloudy nights because clouds absorb IR
radiation from the Sun during the day and emit IR radiation towards the Earth at night
3.
Greenhouse effect is directly related to emission, where certain greenhouse gases
(carbon dioxide) prevent IR radiation from the earths surface to exit back to space
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WATER VAPOUR IN THE ATMOSPHERE
99.9% of water vapour is contained in the troposphere
Condensation of water vapour into liquid or ice is responsible for rain, snow etc The latent heat released during condensation is responsible for cyclones and thunderstorms
Water vapour is also a potent greenhouse gas
Water vapour is most common gas in volcanic emissions (around 60%)
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CARBON DIOXDE IN THE ATMOSPHERE
It is an important greenhouse gas
Natural sources of carbon dioxide in the atmosphere include volcanic activity, combustion of
organic matter, respiration, decay of forests etc
Current carbon dioxide levels (0.0384%) are around 35% higher than the levels in 1832 The concentration of carbon dioxide is higher in the northern hemisphere because it has greater
land mass and plant mass than the southern hemisphere
Carbon dioxide concentrations peak in May(just after the end of winter in the Northern
Hemisphere) and reach a minimum in October (at the end of summer in Northern Hemisphere,
when the quantity of plants undergoing photosynthesis is greatest)
Global Geography #5 | Study Material :: General Studies |IAS Help
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ATMOSPHERIC ELECTRICITY
Overview
Aurora Borealis seen over Canada
The Earths surface, the atmosphere and the ionosphere combine to form a global atmospheric
electrical circuit
Free electricity is always present in the atmosphere. It is usually positive
The intensity of atmospheric electricity is usually greater in the middle of the day than in the
morning or at night. Also, it is greater in winter than in summer
Atmospheric electricity increases with altitude
The Earths surface is negatively charged, while the atmosphere is positively charged
Benjamin Franklin was the first to prove electrical phenomena of the atmosphere in 1752
Variation of atmospheric electricity
The primary cause of variation in atmospheric electricity is the thermodynamics of radiation
Atmospheric electricity is maximum in January and minimum in June
Humidity increases atmospheric electricity in the cold months but decreases it in hot months
PHENOMENA OF ATMOSPHERIC ELECTRICITY
1. Auroras
1.
Auroras are natural light displays observed in the night sky, especially in polar regions
2.
Auroras occur when the Earths magnetic field traps solar wind in the atmosphere
resulting in a collision between the solar wind and atmospheric molecules leading to
release of energy
3.
They are most prominent closer to the magnetic poles because of longer periods of
darkness and strength of the Earths magnetic field
4.
The Aurora Borealis refers to auroras in the northern hemisphere. The corresponding
auroras in the southern hemisphere are called Aurora Australis
5.
Auroras occur most often near the seasonal equinoxes: from September to October and
from March to April
6.
Auroras have maximum intensity during the intense phase of solar cycle when coronal
mass ejections increase the intensity of solar wind
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2.
Static electricity
1.
Static electricity is the build of electrical charge on the surface of objects
2.
The static charge remains on the object until it either bleeds off to the ground or is
quickly neutralized by a discharge
3.
Lightning is caused by discharge of static electricity
3. St. Elmos Fire
1.
St. Elmos Fire is a bright blue or violet glow appearing from tall, pointed objects
2.
It is a phenomenon in which plasma is created when the electric field around the object
causes ionization of air molecules
3.
Sharp objects tend to create more plasma because electrical fields are more
concentrated in areas of high curvature
4.
Lightning
1.
Lightning is an atmospheric discharge of electricity
2.
Occurs during thunderstorms, volcanic eruptions and dust storms
3.
The average lightning bolt can reach temperatures of 30,000 C (about 3 times the
temperature of the sun) and carry around 100 million V of electricity
4.
This extreme temperature compresses surrounding air and creates a supersonic shock
wave called thunder5.
In addition to light, lightning has been shown to emit radio waves, X-rays and gamma
rays
TYPES OF LIGHTNING
Lightning strikes can carry up to 100 million Volts and reach temperatures of 30,000 C
The lightning that is most commonly observed is called streak lightning. This is just the
visible part of the lightning strokethe majority of the lightning occurs inside clouds, so it is not
visible from the Earth.
1. Cloud-to-ground lightning
1.
Second most common form of lightning
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2.
b. Poses greatest threat to life and property since it strikes the ground
2.
Cloud-to-cloud lightning
1.
Lightning occurring between two clouds is called inter-cloud lightning
2.
Lightning that occurs between two areas of the same cloud that have differing electric
potential is called intra-cloud lightning
3. Ground-to-cloud lightning
1.
Lightning discharge between ground and cloud, in the upward direction
2.
Very rare
3.
Occurs when negatively charged ions from the Earths surface rise up and meet the
positive ions in the cloud
4. Heat lightning:lightning that occurs too far away for the sound of thunder to be heard
5.
Dry lightning
1.
Dry lightning is lightning that occurs without precipitation at the surface
2.
This is the most common natural cause of wildfires
3.
Occurs as a result of extreme surface temperatures when convection from the hot
surface to cooler atmosphere leads to lightning
6.
Positive lightning
1.
Occurs when positive charge is carried on the top of clouds2.
Very rare
3.
Around 10 times more powerful and longer lasting than regular negative lightning
4.
Very dangerous to life and property
5. At present, aircraft are not designed to withstand positive lightning
7. Sprite
1.
Large scale discharges occurring high above a thundercloud
2.
Occur about 80 km to 150 km above the Earths surface
3.
Reddish-orange or greenish-blue in colour
4.
May account for aircraft accidents at altitudes above thunderstorms
8.
Blue jets
1.
Occur at lower altitudes than sprites, but still above thunderclouds2.
Occur about 40 km to 80 km above surface
3.
Blue in colour
9.
Elves
1.
ELVES stands for Emissions for Light and Very low frequency Electromagnetic pulse
Sources
2.
Occur in the ionosphere, about 100 km above surface
10.Rocket-triggered lightning
1.
Lightning can be triggered by rockets carrying spools of wire into thunderstorms. When
the wire unwinds, it provides a path for lightning to conduct to the surface
2.
Lightning can also be triggered by space shuttle launches and aircraft flight
11.
Volcanically triggered lightning
1.
Extremely large volcano eruptions which eject gases and material high into the
atmosphere can trigger lightning
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LIGHTNING IN EVERYDAY LIFE
World map showing the frequency of lightning strikes. Lightning strikes most frequently in the Congo
Lightning conductor
It is a metal rod or conductor used to protect a building from lightning
It is mounted on the top of the building and connected to the ground using a wire
When strikes, it will preferentially strike the rod and be conducted harmlessly to the ground
Lightning rods are usually made from good conductors of electricity such as aluminium or
copper
Lightning protection on aircraft
On aircraft, an electrical circuit is established on the aircrafts outer surface
Aircraft made from aluminium naturally act as good conductors of electricity. When the aircraft
is made of carbon composites, a layer of conductive fibre is embedded to ensure conductivity When the aircraft is struck by lightning, current travels on the outer surface of the aircraft,
with the interior remaining unaffected
Proper shielding is provided to ensure lightning does not affect cockpit electronics, fuel tanks
and radar and other avionics
Aircraft also use static dischargers to prevent buildup of static electricity
Trees and lightning
Trees are natural conductors of lightning. They provide connection for lightning to reach the
ground. However, the outer layer of trees (bark) is not a good conductor
Trees get burnt from lightning because lightning travels on the outer surface of the tree,burning away the bark.
Usually, trees can recover from damage to the bark. However, sometimes the damage is too
severe for recovery.
Oak and elm are two trees most frequently struck by lightning. Teak provides the best
conducting connection for lightning
By attracting lightning towards them, trees prevent damage to nearby buildings. However, for
the same reason, it is not safe to seek shelter under trees during lightning
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Shelter from lightning
To get shelter from lightning, there needs to be an electrical connection through the exterior
surface on to the ground. The connection must ensure that people do not get in contact with
the electricity
Best lightning shelters: houses, buildings, closed-roof cars, closed-cabin boats etc
Worst lightning shelters: trees, tents, open barns, open-roof cars, open boats etc
It is unsafe to use radios, cellphones etc during lightning strikes
MEASUREMENT OF ATMOSPHERIC ELECTRICITY
1.
Electrometer
1.
Simple instrument for measuring atmospheric electricity at ground surface
2.
Developed in 1700s by Alessandro Volta
3.
Consists of a glass jar with a pointed metal rod, whose lower end is attached to two
straws. Electricity in the atmosphere cause the two straws to recede from each other,
the amount of divergence indicating the intensity of electricity
2.
Weather balloons
1.
A balloon which carries instruments aloft to send back information regarding
temperature, humidity etc
2.
The device that does the actual measuring is called radiosonde
3.
The radiosonde is an inexpensive device, and it is lost when the life of the balloon
expires
3.
Lightning rocket
1.
It is a device that measures electrostatic and ionic charge in the atmosphere
2.
Consists of a rocket launcher which is in communication with the detection device on
the ground
3. This system controls the time and location of a lightning strike
4.
Uses solid (cesium salts) or liquid (calcium chloride) propellants to produce exhaustgases that act as a conducting pathway between the clouds and the ground
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WIND
Causes of wind
Wind is caused by differences in pressure
It always flows from high pressure to low pressure
The two major driving factors of large scale atmospheric circulation are
o Heating difference between the equator and the poles
o
Rotation of the planet, which leads to air being deflected according to the Corioliseffect. Coriolis effect is the apparent deflection of moving objects when viewed from a
rotating reference frame
Near the Earths surface, friction causes wind to be slowerthan it otherwise would be
Away from the surface, large scale winds tend to approach a state of equilibrium called
Geostropic Balance
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Measurement of wind
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A rock formation in Bolivia, sculpted by wind erosion
Wind direction is reported based on the direction from which it originates. Eg: a northerly wind
blows from the north to the south Wind direction is observed using weather vanes(atop buildings) and windsocks (at airports)
Wind speed is measured using anemometers
Weather balloons and RADAR/LIDAR can also be used for measuring wind speed and direction
Sustained winds are usually observed 10 m from the surface of the Earth
Globally, wind speeds are reported over a 10 minute average. India reports winds over a 3
minute average
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Wind categorization on the Beaufort scale
Beaufort scaleWind speed
(knots)
General termTerminology of IMD
(covers north Indian Ocean)
06 027 Breeze Depression
7 28-33 Gale Deep depression
89 3447 Strong gale Cyclonic storm
1011 4863 Storm Severe cyclonic storm
1216 64120 Hurricane Very severe cyclonic storm
17 > 120 Hurricane Super cyclonic storm
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AEOLIAN PROCESSES
Aeolian process refers to the action of wind in shaping the surface of the Earth.
1.
Wind erosion
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1.
Wind erodes the earth by deflation and abrasion. Deflation is the removal of fine,
loosely grained particles while abrasion is the wearing down of surfaces by grinding
action
2.
Regions that experience intense and sustained erosion are calleddeflation zones
3.
Desert rocks that have been exposed to wind for long periods of time exhibit a dark
shiny stain called desert varnish
4.
Blowoutsare hollows formed by the removal of particles by wind
2. Wind transport
Suspension, saltation and creep
1.
Particles are transported by wind through the processes of suspension, saltation and
creep
2.
Suspension is the holding of small particles in the atmosphere due to upward currents
in air.Dust and haze are examples of suspension.
3.
Saltation is the movement of particles in jumps and skips by lifting up slightly from the
surface. Examples of saltation include sand drift over deserts, soil blowing over fields.
4.
Creep is the slow downward progression of rock and soil down a low grade slope.Creep is responsible for the rounded shape of hillsides
5.
Other wind transport phenomena include dust storms and dust devils. Covered in detail
below.
3. Wind deposition
1.
Wind-deposited bodes occur as sand sheets, ripples and dunes
2. Sand sheets are flat, gently undulating surfaces of sand.They form about 40% of
Aeolian deposition surfaces.
3. Wind blowing on a sand surface also causes ripples,which form into crests and
troughs. In ripples, the coarsest materials collect on the crests
4.
Sand dunes are hills of sandsimilar to ripples, except that they are larger and have the
coarsest materials on the troughs
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ROLE OF WIND IN NATURE
1.
Desert dust migration
1.
Dust from deserts is carried across huge distances over to other continents
2.
Example: dust from the Sahara desert blows via the Caribbean to North America
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3.
Desert dust migration can affect rainfall patterns
4.
It also causes the sky to change colour from blue to white
2.
Effect on plants
1.
The dispersal of seeds through wind is called anemochory
2.
Examples of seeds that disperse through wind: dandelions, maples, weeds
3.
Wind also limits tree growth. The tree line is often lower in coasts and isolated
mountains because high winds reduce tree growth
4.
Wind also causes soil erosion leading to uprooting of trees
3. Effect on animals
1.
Cattle and sheep are prone to wind chill when high wind speeds render their protective
covering inffective
2.
For penguins, their flippers and feet are susceptible as well
3.
Bird migration and insect return tend to flow with wind patterns
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WIND IN OUTER SPACE
1.
Planetary wind
1.
The loss of gas from a planet to outer space is called planetary wind
2.
This happens when light elements such as hydrogen move up to the exobase (limit of
atmosphere), and then reach escape velocity to escape to outer space
3.
The planet Venus is said to have its atmosphere due to planetary wind
2.
Solar wind
1.
Solar wind is a stream of charged particles (plasma) ejected from the sun
2.
This plasma is ejected from the upper atmosphere of the sun at up to 400 km/s
3.
Solar wind creates the heliosphere, a vast bubble in interstellar medium
4.
Planets require large magnetic fields to reduce the ionization of their upper atmosphere
by solar wind. Mars is said to have lost its atmosphere due to solar wind
5.
The surfaces of Venus and the Moon are bombarded directly by solar wind, resulting inhigh radiation levels
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GEOLOGICAL PHENOMENA CAUSED BY WIND
1.
Sand dunes
1.
Sand dunes are hills of sand built by wind
2.
Dunes are usually longer on the windward side and shorter on the leeward side
3.
Sand dunes can form in dry inland regions and also in coastal areas and underwater as
well
4.
Dunes can move over tens of metres due to the consistent action of strong wind.Through saltation, wind picks up particles from the windward side and deposits it on the
leeward side, gradually moving the dune
5. The tallest sand dunes in the world are found in the Namib Desert
2. Erg
1. An Erg is a large area of desert covered with wind-swept sand with little or no
vegetative cover
2.
In essence, ergs are large dune fields
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3.
Ergs are mainly found in Africa, central and western Asia and central Australia
4.
Ergs have been found on Venus, Mars and Titan as well
3.
Loess
The rich fertile soil of the Loess plateau has been the mainstay of Chinese agriculture forcenturies
1.
Loess is a sediment formed by the accumulation of wind-blown silt, sand and clay,
loosely cemented by calcium carbonate
2.
Loess deposits often occur in very thick layers, sometimes more than 100 m thick.It
occurs as a blanket deposit covering areas of hundreds of square km
3.
Loess is highly prone to erosion
4.
Loess can occur from glacial or non-glacial soils. Example of glacial loess: Mississippi
Valley, USA. Example of non-glacial loess: Shanxi, China
5.
Loess tend to develop into highly fertile soils
4. Wind waves
1.
Wind waves are surface waves that occur in oceans, lakes etc due to the action of wind2.
Wind waves can range from ripples to more than 30 m in height
3.
A wind wave system generated by local winds in called wind sea. Wind wave system not
generated by local winds is called swell
4.
Factors that influence the formation of waves include: wind speed, distance of open
water, time duration and water depth
5.
Tsunamis and tides are specific types of waves caused not by wind, but by geological
effects. They have longer wavelength than wind waves
6.
Waves can be measured using buoys that record the motion of the water surface
7.
A breaking wave is one whose one can no longer support its top causing it to collapse
8.
There are three main types of waves
1.
Spilling or rolling waves: Safest waves for surfing.Most common type of wavesfound at shores.
2. Plunging or dumping waves: preferred by experienced surfers.Found where
there is a sudden rise in ocean floor like a sandbar
3. Surging waves: very dangerous for surfing.Tend to form on steep shorelines,
where the depth results in waves not breaking as they approach the shore
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GEOGRAPHICAL FEATURES SHAPED BY WIND
FeatureLocation Wind effect Notes
Mississippi River
Alluvial Valley South-central USA Glacial loess
Loess plateauShanxi, Northern China
Non-glacialloess
Thickest loess in the world (335
m)
Most erodible soil on earth
Selima sand sheetEgypt, Sudan
Wind
depositionLargest sand sheet
Namib desert sand
dunes Namibia, AngolaWind
deposition
Oldest desert in the world (55
million years)
Paha Iowa, USA Sand dunes
Badain Jaran desert Inner Mongolia (China,Mongolia)
Sand dunesTallest stationary sand dunes in
the world (500 m)
Great dune of PilatFrance Sand dune Largest sand dune in Europe
MerhebUAE Sand dune Used for motor sports
Kelso dunesUSA Sand dune
Cerro BlancoSechura Desert, Peru Sand dune Highest sand dune in the world
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WIND CIRCULATION
Overview
The global circulation patterns of wind on Earth
Winds that blow predominantly from a single direction over a particular point on the Earths
surface are called Prevailing Winds
The general trends in wind direction are called dominant winds
In general regional winds can be divided into two groups
o Global windslike easterlies, westerlies
o Local windslike land breeze, sea breeze
Prevailing winds greatly influence climate patterns such as rainfall gradients, where the
windward side of mountains have high rainfall while leeward side experience desert conditions
Wind roseis a graphic plotting tool that is used to describe the speed and direction of wind at a
particular location
Insects drift along prevailing winds, while birds are able to fly independent of them
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Distribution of prevailing winds
In general, easterly winds flow at low and high altitudesi.e. near the tropics and the poles
Westerly winds flow at the mid-latitudes
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Directly under the subtropical ridge i.e. close to the equator, winds are lighter in intensity. These
subtropical regions are called the doldrums, or horse latitudes
The strongest winds are usually in the mid-latitudes,where cold air from the Artic meets warm
air from the tropics
Most of the earths deserts are found near the subtropical ridge,with high pressure leading to
low humidity
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GLOBAL WINDS
Trade Winds
o Trade winds are the prevailing easterly winds that blow across the tropics
o They blow from the northeast in the northern hemisphere and from the southeast in the
southern hemisphere
o Trade winds act as the steering for tropical storms that form in the Atlantic, Pacific
and south Indian Oceans.These storms make landfall in North America, Southeast Asia
and India, respectivelyo Trade winds steer African desert dust across the Atlantic Ocean towards North
America(esp. the Caribbean and Florida)
o The weaker a trade wind becomes, the more rainfall it brings
o Trade winds are stronger in winter than summer
o The one region of the Earth where trade winds are absent is the north Indian Ocean
Westerlies
o Westerlies are the prevailing winds in the mid-latitudes i.e. between 35 and 65
degrees latitude
o They blow from high pressure areas in the horse latitudes towards the poles
o Westerlies blow from the southwest in the northern hemisphere and from the
northwest in the southern hemisphere
o
Westerlies are instrumental in carrying warm equatorial winds towards the western
coasts of continents
o They are responsible for carrying desert dust from the Gobi Desert into North America
o They are stronger in winter than in summer, and over regions that have less land to
interrupt their flow. They are stronger in the Southern Hemisphere because of the vast
ocean expanses uninterrupted by land mass
o Westerlies are strongest in the Roaring Forties i.e. between 40 and 50 degrees latitude
Polar Easterlies
o Polar easterlies are the prevailing winds that blow at the north and south poles
o They are cold and dry winds
o They blow from high pressure areas near the poles towards low pressure areas within
the mid-latitudeso They blow from the east to the west
o Polar easterlies are often weak and irregular
o They are also called Polar Hadley Cells, named after George Hadley who discovered
them in 1753
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LOCAL WINDS
Notable local winds
1. Sea and land Breeze1.
Sea and land breezes are caused by the temperature differential between the sea and
coastal areas
2.
Sea breeze occurs when the land gets heated during the day creating a low pressure,
and cool air from the sea rushes in
3.
Land breeze occurs when the land cools off rapidly at night causing low pressure over
the sea, and warm air flows from the land to the sea
4.
Sea breeze occurs during the day while land breeze occurs at night
2. Mountain winds
1.
In elevated surfaces heating of the ground exceeds heating of surrounding air, thereby
changing wind circulation
2.
Hills and valleys significantly distort airflow by acting as physical barriers. This is known
as barrier jet
3.
Jagged terrain results in unpredictable flow patterns and turbulence
4.
Passes in the mountain range experience lower pressure resulting in high wind speeds
and erratic and turbulent air currents
5.
These conditions are dangerous to ascending and descending airplanes
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MONSOON WINDS
Overview
Monsoons are defined as seasonal reversing winds accompanied by seasonal changes
in precipitation
The major monsoon systems of the world are the West African and Asia-Australian
monsoon systems
The origin of monsoons about 15-20 million years ago has been linked to the uplift of
the Tibetan Plateau after the collision of India and Asia 50 million years ago
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Cause of monsoons
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Monsoons are caused by the larger amplitude of seasonal land temperature cycle
compared to that of nearby oceans. This temperature differential arises because air
over land warms faster and reaches higher temperature than the air over nearby ocean
The hot air over land tends to rise creating a low pressure
This creates a steady wind blowing from the ocean towards land, bringing moist air from
the oceans
In winter the land cools off quickly creating a high pressure that blows wind from land to
sea
In essence, monsoons are similar to sea and land breezes, except that they occur on a
much larger scale
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The Southwest Monsoon
The Southwest monsoon in India. It brings about 80% of India's annual rainfall
The southwest monsoon occurs from June to September
The southwest monsoon is caused by rapid heating of the Thar desert and north-central India in
summer, creating a low pressure that is filled by moisture laden winds from the Indian Ocean
The Himalayas prevent the wind from blowing towards Central Asia and redirect them inwards
to cause rainfall
The Arabian Sea branch of the southwest monsoon brings rainfall to the Malabar coast andcentral India
The Bay of Bengal branch of the southwest monsoon picks up additional moisture in the Bay of
Bengal and arrives at the eastern Himalayas, and then turns west towards the Indo-Gangetic
plains
Mawsynram in Shillong is the wettest place on Earth with about 12,000 mm of rainfall
annually
The traditional start date of the southwest monsoon is June 01
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The southwest monsoon accounts for 80% of rainfall in India
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The Northeast Monsoon
The northeast monsoon occurs October to December in India Around September, northern India begins to cool rapidly creating a high pressure zone
This brings dry cold winds from the Himalayas towards the Deccan and into the Indian Ocean
While travelling towards the Indian Ocean, the wind picks up moisture in the Bay of Bengal and
pours it over southern peninsular India
The northeast monsoon accounts for 50-60% of rainfall in Tamil Nadu
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JET STREAMS
Overview
The polar and subtropical jet streams
Jet streams are fast, narrow air currents in the atmosphere
Jet streams are usually located near the tropopause (transition between troposphere and
stratosphere)
The main jet streams are westerly winds, flowing from the west to the east
Jet streams are used for weather forecasting and aviation. It is hypothesised that they could be
used as an energy source as well
Jet streams have been observed in the atmosphere of Jupiter as well
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Cause of jet streams
Jet streams are caused by a combination of atmospheric heating and the rotation of the earth
They form near boundaries of adjacent air masses with significant differences in temperature
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Occurrence of jet streams
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The strongest jet streams are the polar jets (23,000-39,000 ft) and the somewhat weaker
subtropical jets (33,000-52,000 ft)
Other weaker jets also exist, especially over central USA
There is one polar jet stream and one subtropical jet stream each in the northern and southern
hemispheres
The northern hemisphere polar jet is situated over the northern latitudes of North America,
Europe and Asia, while the southern polar jet always circles Antarctica
The northern and southern hemisphere jet streams have been found to be drifting towards the
poles at a rate of 2.1 km per year
Jet streams are typically a few hundred miles wide and about 3 miles thick vertically
Wind speeds usually exceed 92 km/h, although speeds of over 398 km/h have been observed
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Jet streams and aviation
Jet streams are often as the preferred flight plans for commercial airliners
Flying with the jet streams decreases travel time and reduced fuel consumption Conversely, flying against jet streams can add to travel time and increase fuel consumption. For
this reason, flight plans use circuitous routes to avoid flying against jet streams
Commercial use of jet streams began in 1952 on the Tokyo-Honolulu route cutting travel time
from 18 hours to 11.5 hours
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A FEW NOTEWORTHY LOCAL WINDS
Wind Location Description
CalimaSahara to Canary Islands
(west African coast)Carries dust from the Sahara
Chinook Rocky mountains Warm, dry westerly winds
Elephanta Malabar coastSouth easterly wind
Marks end of southwest monsoon
Noreaster North east USA Strong storm winds from the northeast
Norwester East coast of New Zealand Warm dry winds
Santa Ana
windsSouthern California
Strong, extremely dry winds
Responsible for frequent wildfires
Sirocco North Africa, Europe
Strong winds from the Sahara that cause dusty dry
conditions in north Africa and cold wet conditions in
Europe
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Reaches hurricane speeds, can last hours to days
Shamal Persian GulfStrong Northwesterly wind
Causes large sandstorms in Iraq
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ROCKS
Overview
Rocks are naturally occurring solid aggregates of minerals or mineraloids (a mineral-like
substance that does not exhibit crystallinity)
The Earths outer solid layer, the lithosphere, is made of rocks
Rocks are generally classified into three types
o Igneous rocks
o Sedimentary rocks
o Metamorphic rocks
The structure and composition of rocks change over time, causing one type of rock to be
reclassified as another
The study of rocks is called petrology
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IGNEOUS ROCKS
Overview
Igneous rocks are rocks which form from the cooling and solidification of magma
They are the results of volcanic processes
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The magma can be derived from melts of pre-existing rocks in either the crust or mantle.
Typically, rocks melt under conditions of extremely high temperatures, low pressures or changes
in composition
Igneous rocks can be of two types:
o Intrusive (plutonic) rocks
o Extrusive (volcanic) rocks
Igneous rocks make up about 90% of the Earths crust.However, they are hidden from the
surface by a thin layer of sedimentary and metamorphic rocks
Igneous rocks can be seen at mid ocean ridges, areas of volcanism and intra-plate hotspots
They are crystalline and impervious
They are resistant to erosion and weathering
Geological significance of igneous rocks
Crystallisation of magma leading to igneous rocks
Since igneous rocks come from the mantle, the minerals and chemistry of igneous rocks give
information about the composition of the mantle
Their features are characteristic of a particular tectonic environment, allowing reconstitution of
tectonic conditions
They host important mineral deposits such as uranium, tungsten, tin, chromium, platinum
Mineralogical composition of igneous rocks
Felsic rock: highest content of silicon with predominance of quartz and feldspar. These rocks are
usually light coloured and have low density
Mafic rock: lesser content of silicon, predominance of mafic minerals (manganese and iron).
These rocks are usually dark coloured and have higher density than felsic rocks
Ultramafic rocks: lowest silicon content, with more than 90% of mafic minerals
Felsic Mafic Ultramafic
Intrusive Granite Gabbro Peridotite
Extrusive Rhyolite Basalt Komatite
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Intrusive igneous rocks (plutonic rocks)
Intrusive igneous rocks are formed from magma that cools and solidifies within the crust
These rocks are coarse-grained. Mineral grains in these rocks can be identified by the naked eye
The central cores of most mountain ranges are made of intrusive rocks (usually granite). Theselarge formations of intrusive rocks are called batholiths
Examples of intrusive igneous rocks include granite and diorite
Extrusive igneous rocks (volcanic rocks)
Extrusive igneous rocks are formed at the surface, from magma released into the surface from
volcanic eruptions
Extrusive rocks cool and solidify quicker than intrusive
Extrusive rocks are fine grained in nature
Examples of extrusive rocks include basalt and rhyolite
Large Igneous Province (LIP)
The Deccan Traps in the Western Ghats
Large Igneous Provinces are extremely large accumulations of igneous rocks (both intrusive and
extrusive)
They refer to igneous rocks extending over 100,000 sq km, that formed in a short geological
time scale of a few million years or less
LIPs usually consist of basalt and rhyolite rocks When created, LIPs often have an area of few million sq km and volume on the order of a million
cubic km. Majority of the LIPs volume is emplaced in less than a million years.
LIPs are postulated to arise from hotspots of linear chains of volcanoes
LIPs are often linked to mass extinction events. This is said to arise from the enormous
quantities of sulphuric acid released into the atmosphere, the subsequent global cooling and
absorption of oceanic oxygen.
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The Deccan Traps, one of the largest volcanic features on Earth, is an example of a Large
Igneous Province. The Traps consist of multiple layers of basalt, more than 2 km thick and cover
an area over 500,000 sq km, and were formed as a result of volcanic eruptions in the Western
Ghats about 66 million years ago. It is believed that the enormous volcanic eruptions led to
global cooling of around 2C, and were instrumental in the mass extinction of non-avian
dinosaurs.
SEDIMENTARY ROCKS
Overview
Sedimentary rock is the type of rock formed sedimentation of material.This sedimentation can
occur on the Earths surface or within bodies of water
Sedimentary rocks form the thin outermost layer of the earths crust, making up about 5% of
the total volume of the crust
Sedimentary rocks are deposited in strata called bedding
Coal is a sedimentary rock
Examples of sedimentary rocks include shale, sandstone, limestone
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Geological significance of sedimentary rocks
Sedimentary rocks are the only rocks that contain fossils
Study of sedimentary rocks provides information about subsurface, which is important in civil
engineering for construction of roads, bridges etc
Sedimentary rocks are also important sources of natural resources like fossil fuels, water, ores
etc The study of sedimentary rock strata serves as the main source of scientific knowledge about
the Earths geological history
Sedimentary rocks are the only rocks that contain fossils.Sedimentary rocks contains fossils
because, unlike igneous and metamorphic rocks, they form at temperatures and pressures that
do not destroy fossils
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Composition of sedimentary rocks
Most sedimentary rocks contain either quartz or calcite
Unlike igneous and metamorphic rocks, sedimentary rocks do not contain multiple major
minerals
Carbonate rocks contain carbonate minerals like calcite, aragonite or dolomite
Siliclastic rocks contain silica-bearing minerals like quartz
Clastic sedimentary rocks
Clastic rocks are composed of fragments, called clasts, of pre-existing rocks
Clastic sedimentary rocks are those that are formed from rocks that have been broken down
due to weathering, which are then transported and deposited elsewhere
Clastic sedimentary rocks come in various grain sizes. They range from fine clay in shales, to
sand in sandstone and gravel, cobbles and boulder size fragments in conglomerates and breccias
Conglomerates are clastic sedimentary rocks with rounded fragments, while breccias consist of
clasts with angular fragments. Both conglomerates and breccias contain clasts larger than sand
(> 2 mm)
Examples include shale, sandstone, siltstone
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Organic sedimentary rocks
Organic sedimentary rocks contain materials generated by living organisms
They usually contain carbonate minerals generated by these organisms
Examples include corals, chalk, coal and oil shale
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Chemical sedimentary rocks
Chemical sedimentary rocks are formed from minerals in solution that become oversaturated
They usually occur as a result of evaporation
Examples include limestone, barite, gypsum
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METAMORPHIC ROCKS
Overview
Metamorphic rocks form as a result of transformation of an existing rock, in a process called
metamorphism. The existing rock is calledprotolith
Metamorphic rocks are formed when theprotolithsare subject to extreme temperatures and
pressures
They form from tectonic process, intrusion of magma, or simply by being deep beneath the
earths surface (being subject to high temperatures and pressures of rock layers above)
Much of the lower continental crust is metamorphic
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Examples of metamorphic rocks include gneiss, slate, marble
Composition of metamorphic rocks
Metamorphic rocks are composed of metamorphic minerals
Metamorphic minerals are those that form only at high temperatures and pressures.Theseinclude sillimanite, kyanite, andalusite, staurolite and garnet (all of which are silicates)
Metamorphic rocks also contain smaller amounts of micas, feldspars and quartz. However,
these are not products of metamorphism, and are instead leftovers from theprotoliths
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Contact metamorphic rocks
Contact metamorphic rocks are those that form when magma is injected into surrounding rock
The cooling magma leads to igneous rocks, and around this is a zone called contact
metamorphism aureolewhere metamorphic rocks are formed
The extreme temperatures cause sandstones to metamorphise into quartz, limestone intomarble and shale into cordierite
Igneous rocks are harder to transform than sedimentary rocks since they form at even greater
temperatures
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Regional metamorphic rocks
Regional metamorphic rocks are those that form due to metamorphism over a wide area
Regional metamorphism tends to make rocks foliated
Regional metamorphic rocks tend to form at great depths simply under the temperature and
pressures of upper layers of rock Continental crusts are examples of regional metamorphic rocks
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IMPORTANT ROCK TYPES
Rock Classification Composition Notes
BasaltIgneousextrusive
volcanicFeldspar, pyroxene
Present on moon, Mars, Venus
Basalt rocks sustain microbial life
Fine texture
GraniteIgneous (intrusive,
felsic)Quartz, feldspar
Coarse texture
Massive, hard and tough
Exhibit radioactivity (uranium)
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Shale Sedimentary (clastic) ClayContain organic matter
Contains multiple thin layers
Limestone SedimentaryCalcite (calcium
carbonate)
Used in quicklime, mortar, cement, concrete
Soluble in water
Host of most cave systems
Sandstone Sedimentary Quartz, feldspar
Common building material
Porous, allows water percolation
Host of water aquifers and petroleumreservoirs
Slate Metamorphic Clay, volcanic ash
Used to make roofing, flooring
It is an electrical insulator, used forswitchboards
Can host even microscopic amounts of
fossils
Gneiss Metamorphic Garnet, biotite
Marble Metamorphic
Calcite
(calciumcarbonate)
Comes from metamorphism of limestone
Pure white marble comes from pure
limestone
Colours, swirls, veins come from mineralimpurities
Important source of calcium carbonate,used in toothpaste, paint
Quartzite Metamorphic Quartz
Comes from metamorphism of sandstone
Used as a decorative stone
Used for railway ballast
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IMPORTANT ROCK FORMATIONS/STRUCTURES
For a full list of rock formations see here
For a list of fascinating rock formations, see here
http://en.wikipedia.org/wiki/List_of_rock_formationshttp://en.wikipedia.org/wiki/List_of_rock_formationshttp://www.oddee.com/item_96838.aspxhttp://www.oddee.com/item_96838.aspxhttp://www.oddee.com/item_96838.aspxhttp://en.wikipedia.org/wiki/List_of_rock_formations8/11/2019 General Study Geo 1to8
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Formation/structure Location Classification Notes
Deccan TrapsDeccan Plateau,
India
Large Igneous
Province (LIP)
One of the largest volcanic
features on earth
Siberian Traps Siberia, Russia LIP One of the largest known volcanicevents (250 million years ago)
Acasta Gneiss Quebec, Canada MetamorphicOldest known rock in the world
(4.28 billion years)
Devils Tower Wyoming, USA IgneousMonolithic rock that rises 1200
feet above surrounding terrain
Blue Lias England Limestone and shale Rich in dinosaur fossils
Red Fort Delhi Sandstone
Hawa Mahal Jaipur Sandstone
Mahabalipuram
sculpturesMahabalipuram Granite
Mount Augustus Western AustraliaSandstone and
conglomerateLargest monolith in the world
Savandurga Karnataka Gneiss and granite Largest monolith in India
Sphinx Egypt Limestone
Oldest known monumental
sculpture
Largest monolith statue in world
Phobos monolith Mars Igneous
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