Geography Climatology
Geography Climatology
Geography Climatology
Antarctic Circumpolar Current
Strongest ocean current extends from the sea surface to the bottom of the ocean and encircles Antarctica
Vital for Earth’s health because it keeps Antarctica cool and frozen
Provides the main connection between the Indian, Pacific and Atlantic Oceans
Flows through Drake Passage between South America and Antarctica
Steep undersea mountains constrain its path and steer it north and south across the Southern Ocean
Influences Meridional Overturning Circulation carries warm waters from tropics north towards Atlantic Ocean
NASA’s Orbiting Carbon Observatory
El Nino led to excessive carbon releases
Wildfires in SE Asia due to hot weather and droughts
Drought in Amazon rainforest which reduced plant growth and reduced the amount of carbon they absorb while growing
Polar Vortex
Whirling cone of low pressure over the poles
Strongest in the winter months due to the increased temperature contrast between the polar regions and the midlatitudes
Spins in the stratosphere
When the vortex is strongest, cold air is lesslikely to plunge deep into North America or Europe forms a wall that protects the
midlatitudes from cold Arctic air
Occasionally, the polar vortex is disrupted and weakens, due to wave energy propagating upward from the lower atmosphere >
the stratosphere and Arctic warms sharply (sudden stratospheric warming)
Warming weakens the polar vortex, shifting its location south of the pole or ‘splitting’ the vortex up into ‘sister vortices’.
Weakening of Polar Vortex leads to a warm Arctic
Effects
Declining temperatures and extreme winter weather in the eastern US along with northern and western Europe.
Sudden stratospheric warming also leads to a warm Arctic not only in the stratosphere but also in the troposphere as well.
Warmer Arctic, in turn, favours more severe winter weather in the Northern Hemisphere midlatitudes (polar vortex weakens,
'spills' south)
‘Beast from the East’, the blast of cold weather that blew from Siberia towards western Europe and the UK in February and
March of 2018
Stratocumulus clouds
Stratocumulus clouds are lowlevel clumps or patches of cloud varying in colour from bright white to dark grey.
Most common clouds on earth recognised by their welldefined bases with some parts often darker than others.
Usually have gaps between them, but they can also be joined together.
Usually form from a layer of stratus cloud upon breaking up. Indicators of a change in the weather and are usually present near
a warm, cold or occluded front.
Can be present in all types of weather conditions, from dry settled weather to more rainy conditions
Do not cause severe rain
Marine clouds that protect us from hothouse Earth conditions by reflecting sunlight back into space could break up and vanish if CO2
in the atmosphere triples
Stratocumulus clouds cover about 20% of subtropical oceans, mostly near western seaboards such as the coasts of California,
Mexico and Peru
When they disappear, Earth warms by about 8° C — in addition to the global warming that comes from enhanced greenhouse
concentrations alone
A temperature increase of that magnitude would melt polar ice and lift sea levels tens of metres
Sagar Nidhi
Indian Ocean Research Vehicle, which is a part of IndiaUS expedition
Funded by Ministry of Earth Sciences and US Office on Naval Research
Investigate irregularities in SW monsoon
Data from different depths and locations to understand interactions of atmosphere with upper level of sea
CUSAT Stratosphere Troposphere 205 Radar
Situated in Cochin, indigenously built radar to scan stratosphere over the Indian Ocean for air movements
Weather radars detect perturbations in wind and water content of atmosphere
Scans using radio waves to create a 3D picture of the atmosphere
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Spring equinox
First official day of spring in the Northern Hemisphere
Length of day and night are close to equal.
At the equinox, earth’s two hemispheres are receiving the sun’s rays equally
Night and day are often said to be equal in length.
Moment in Earth’s orbit when the sun appears to cross the celestial equator
Vernal equinox also is the Persian New Year Navroz
Chichen Itza, Mexico (Kulkulkan pyramid) In the late afternoon, the sun creates a shadow that looks like a snake sliding down
the northern staircase
LPA Long Period Average
Average rainfall received by the country as a whole during the southwest monsoon (June to September), for a 50year period
Current LPA is 89 cm, based on the average rainfall over years 1951 and 2000
Acts as a benchmark against which the rainfall in any monsoon season is measured
IMD maintains an independent LPA for every homogeneous region of the country
Monthly LPA decreases from June to September
Categories
Normal: +/10% of LPA
Below normal: 9096% of LPA.
Above normal: 104110% of LPA.
Deficient: Less than 90% of LPA.
Excess: More than 110% of LPA.
Rainfall in the SW monsoon season was normal (90% of LPA)
NE monsoon rainfall was well below normal (56% of LPA, 6th lowest since 1901)
Aurora
Display of light in the sky predominantly seen in the high latitude regions (Arctic and Antarctic)
Also known as a Polar light
When charged particles from the solar wind collide with air molecules above Earth’s magnetic poles, it causes the air molecules
to glow, causing the auroras – the northern and southern lights
Aurora borealis (northern lights) and Aurora australis (southern lights)
Less frequent in middle latitudes
Sun’s energy in the form of solar wind, is behind the whole process
Auroras affect communication lines, radio lines and power lines
Provoked by energy from the Sun and fueled by electrically charged particles trapped in Earth’s magnetic field
Caused by collisions between fastmoving electrons from space with the oxygen and nitrogen in Earth’s upper atmosphere
Electrons from Earth's magnetosphere transfer their energy to the oxygen and nitrogen atoms and molecules, making them
“excited”.
As the gases return to their normal state, they emit photons, small bursts of energy in the form of light
When a large number of electrons come from the magnetosphere to bombard the atmosphere, the oxygen and nitrogen can emit
enough light for the eye to detect, generating the aurora displays
Colour depends on
Which gas — oxygen or nitrogen — is being excited by the electrons
How excited it becomes
How fast the electrons are moving
Western Disturbance
Extratropical storm originating in the Mediterranean region
Brings sudden winter rain to the northwestern parts of the Indian subcontinent
Nonmonsoonal precipitation pattern driven by the westerlies
Extratropical storms have moisture usually in the upper atmosphere, unlike tropical cyclones where the moisture is carried in the
lower atmosphere
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Impact
Plays an important role in bringing moderate to heavy rain in lowlying areas and heavy snow to mountainous areas of the Indian
Subcontinent
Associated with cloudy sky, higher night temperatures and unusual rain
Importance in agriculture, particularly for the Rabi crops
Excessive precipitation due to this disturbance can cause crop damage, landslides, floods and avalanches
Over the IndoGangetic plains, it occasionally bring cold wave conditions and dense fog
Earth has a geoid shape flattened at poles
Angle of sun’s rays goes on decreasing towards the poles
Tropic of Cancer and Tropic of Capricorn
Torrid Zone
Midday sun is exactly overhead at least once a year, and this area receives maximum insolation
Tropic of Cancer and Arctic Circle, Tropic of Capricorn and Antarctic Circle
Temperate Zone Moderate temperatures
Mid day sun never shines overhead
Arctic Circle and North Pole, Antarctic Circle and South Pole
Frigid Zone
Mid day sun never shines overhead
Latitude Longitude
Become smaller in length (circumference) towards the poles Same length for all longitudes
Angular distance of a point from centre of earth Angular distance of a point from centre, along the equator
Linear distance between two consecutive latitudes separated Area enclosed between two longitudes decreases towards the
by angular distance 1° is greater towards the poles poles
Equator as reference point Prime Meridian (Greenwich) as reference point
Countries with large longitudinal extent find it convenient to have multiple time zones
International Date Line
Date changes by exactly one day when it is crossed
W to E —> Gain a day
E to W —> Lose a day
Passes in midPacific deviates from the 180° longitude at Bering Strait, Fiji, Tonga, groups of islands (Polynesia, Melanesia,
Micronesia)
IST 82.5°E
Chaibagaan Time Observed by tea planters 1 hour ahead of IST (improving productivity by optimising use of daytime)
Rotation of Earth
Earth rotates along tis axis from W to E
Circle of illumination Circle that divides day from night on the globe
Tilted axis of rotation 23.5° to the normal, 66.5° to the orbital (plane of earth’s orbit around the sun)
Rotation causes day and night
Why are days longer than nights at the equator?
Due to atmosphere, sun’s rays get refracted and the apparent position of sun is above the horizon (as we see in a straight line) even
when the sun is below the horizon in early morning and late evenings)
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Why does temperature fall as we move towards the poles?
Geoid shape of earth and position of the sun energy received per unit area decreases from equator towards poles
Equator receives direct sunlight, while poles receive slant sunlight
Revolution of Earth
Sun rays overhead of Tropic of Cancer
NP inclined towards sun 6 month day in Arctic Circle (whole arctic circle within circle of
Summer Solstice 21 June
illumination)
Longest day and shortest night in the Northern Hemisphere
Sun rays on Equator
Autumn Equinox 23 September
Equal day and night
Sun rays overhead of Tropic of Capricorn
Winter Solstice 22 December SP inclined towards sun 6 month day in Antarctic Circle
Longest day and shortest night in Southern Hemisphere
Sun rays on Equator
Spring Equinox 21 March
Equal day and night
Revolution causes seasons (Rotation causes day and night)
If there was no tilt, each point on earth would have 12h day and 12h night
Daylight saving
Practice of advancing clocks in the summer
Evening time is increased by sacrificing morning
Reduces evening use of energy
ATMOSPHERE
Because of force of gravity, atmosphere is inseparable from earth
Atmospheric Pressure Pressure of air on earth’s surface by virtue of its weight
Regulates entry of solar radiation
Moderates temperature
Shields harmful UV radiation
Permanent Gases of the atmosphere Nitrogen > Oxygen > Argon > CO2
Oxygen upto 120km
Carbon dioxide and Water Vapour upto 90km
Constituents of Atmosphere
Nitrogen 78%, Inert Gas, Controls combustion by diluting oxygen
21%, Combines to form oxides, Combustion not possible without oxygen
Oxygen
Upto altitude 120km
CO2 0.03%, Upto altitude 90km
Transparent to incoming short radiation but opaque to outgoing long radiation
Absorbs part of terrestrial radiation and reflects it back towards the surface
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Most important factor in heat energy budget and climate change due to fossil fuel emissions
Between 10 and 50km above the earth surface, but greatest concentration between 2025 km
Forms at higher latitudes and transported downwards
Ozone
Blocks UV radiation from the sun
Small proportions at the surface, but important in GH effect
Variable gas tropics 4% by volume, dry/cold deserts and polar areas <1%
Decreases with altitude (90% within 6km, negligible after 90km) and from equator towards poles
Absorbs parts of incoming waves apart from outgoing radiation moderates temperature
Contributes to stability and instability in the air
Water Vapour
On condensation, it releases latent heat of condensation which is the driving force behind all storms
Most abundant and significant GHG
Moisture in air decides quantity of latent heat stored development of storms and cyclones
Affects physiology of organisms
Originate from sea salts, soil, smoke, ash, pollen, dust
Generally concentrated in lower layers, but convectional currents may transport them to great heights
Higher concentration in temperate/sub tropical regions due to dry winds compared to equatorial/polar regions
Dust Particles Form hygroscopic nuclei around which water vapour condenses to from clouds
Absorb, reflect and scatter radiation
Blue colour of sky is due to selective scattering by dust particles
Responsible for orange and red colours at sunrise and sunset, and length of dawn and twilight
Produced by decomposition of biological matter
Methane
GHG
Structure of Atmosphere
8km near the poles and 18km near the equator (greater at equator because heat is transported to
great heights due to convectional currents)
Contains dust particle and water vapour
Troposphere
All weather change phenomena
Most important layer for all biological activity
Temperature falls with altitude at rate 6.5°C/km —> Lapse Rate
Separates troposphere and stratosphere
Tropopause Constant temperatures
Temperature over Equator 80°C and temperature above poles 45°C
Extends to a height of 50km
Contains the ozone layer
Stratosphere Free from clouds and weather disturbances ideal for aircrafts
Temperature increases with altitude due to presence of ozone
Cirrus clouds are sometimes present in lower Stratopshere
Above the stratosphere and extends upto a height of 80km
Mesosphere Temperature falls with altitude
Meteorites burn up in this layer upon entering the atmosphere
Temperature rises with altitude due to radiation of sun
Even though temperature is high, heat is not felt as the atmosphere is extremely rarified
ISS and satellites orbit in this layer
Auroras in lower thermosphere
Thermosphere
Ionosphere is a part of it (80400 km) radio waves transmitted from earth are reflected back to earth by this
layer
Electrically charged due to ionisation of atoms
Beyond ionosphere above a height of about 400km
Air is extremely rarified
Exosphere
Light gases like Helium and Hydrogen float into the space from here
Karman Line Boundary between earth’s atmosphere and outer space
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TEMPERATURE DISTRIBUTION
Earth receives all of its heat from the sun and radiates back this energy to the space —> Neither warms up nor cools down
Earth absorbs short wave radiation during the day and reflects back the heat received as long wave radiation at night
Variation in heat received by different parts of the Earth causes Pressure differences leads to transfer of heat from one region to
another
Earth intercepts 1/2 billion parts of solar radiation —> Insolation
Sun rays fall obliquely on earth’s surface —> very small portion is intercepted
Volcano, Springs and Geysers transfer heat within core and mantle to the surface and ocean bottoms —> Negligible compared to that
received from the Sun
Methods of heat transfer
Radiation Heat transfer from one body to another without actual contact/movement
Atmosphere is indirectly heated by radiation from lower altitudes therefore, higher altitudes are cooler
Conduction Heat transfer through matter by molecular activity (contact) transfer takes place till both bodies are at same
temperature
Air in contact with land gets heated slowly
Conduction is most important in heating lower layers of the atmosphere
Convection Transfer of heat energy by actual transfer of matter (convection cycles in sea and atmosphere)
Air in contact with land rises vertically after being heated by conduction and heats the upper layers
Only in troposphere
Advection Heat transfer by horizontal movement of air
In middle latitudes, most of the diurnal variation in temperature is caused by advection alone
Loo is an outcome of advection
Factors affecting temperature distribution
Duration and direction of sunshine
Day/night, clear sky/overcast, summer/winter
Inclination of sun rays is determined by the latitude
Higher latitudes make less angle with surface of earth —> More slant sun rays —> More area over which the sun rays fall
leading to less energy received per unit area, Slant rays pass through greater thickness of atmosphere resulting in more
absorption
Transparency of atmosphere
Scattering When wavelength of radiation is more than wavelength of particle scattering causes red colour of rising and setting
sun, and the blue colour of the sky
Blue light is scattered the most (least wavelength) Because of this an observer sees blue light from all directions but red light
coming from only the sun
Internal Reflection Wavelength of radiation is less than wavelength of particle
Absorption If obstructing particles are of ozone, water vapour, carbon dioxide
LandSea differential
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Albedo of land > Albedo of oceans
Average penetration of sunlight is more in oceans than in land (20m as against 1m)
Convection cycle in oceans helps in heat exchange between layers which keeps diurnal and annual ranges of temperature low
Specific heat of water = 2.5x that of landmass
Prevailing winds and air masses
Exchange of heat between land and water bodies
Oceans moderate the climate in coastal areas
Winds generate currents which have a role to play in controlling temperature
Distance from Sun
Variations in distance between Earth and Sun causes very slight differences in insolation received at the top of the atmosphere
—> Effect of this small difference is masked by factors like distribution of land and sea and atmospheric circulation
Slope
Direction of slope and its angle determines availability of sunlight exposed slopes are drier
With irrigation, these slopes are suitable for agriculture as they receive sunlight
Spatial distribution
Amount of insolation varies across latitudes
At the same latitude, insolation is more over continents than over oceans
Equator receives less insolation than tropics tilt of earth, cloud cover over equator
Maximum insolation over subtropical deserts where cloudiness is least
Maximum diurnal ranges are in continents (continentality no moderating influence of oceans)
Minimum diurnal ranges are in oceans mixing of water and high specific heat of water
Northern Hemisphere is hotter than Southern Hemisphere due to large landmasses in North
Mountains like Rockies and Alps prevent oceanic moderating influence from going inwards
Highest temperatures in India are in May, instead of in summer solstice because monsoons set in during the summer solstice period
Energy surplus 040° N/S Incoming Radiation > Outgoing Radiation
Energy deficit 40°90° N/S Incoming Radiation < Outgoing Radiation (Slant sunlight, High albedo of polar regions)
Planetary Winds and Ocean Currents transfer excess heat from tropics towards poles
Isotherm
Imaginary line joining places with equal temperature
Shows latitudinal distribution of temperature
Generally follow the latitudes but show deviations at landocean boundaries migrate towards equator in winter and pole ward
in summers over land
Similarly when they pass over warm currents, they migrate polewards Gulf Stream and North Atlantic Drift in the Northern
Atlantic Ocean
Deviation is more prominent in January than in June, especially in Northern Hemisphere
Deviation more over northern hemisphere due to larger amount of landmass landocean contrast and effect of currents
Temperature Gradients
Narrow distance between isotherms shows high thermal gradient
High gradients over middle and higher latitudes, Weak gradients over Tropics which receive insolation throughout the year
Low gradients over eastern margins of continents due to warm ocean currents (and high over western margins due to cold
currents)
Seasonal Distribution
JANUARY
Northern Hemisphere Winter JANUARY
Western margins of continents are warmer than eastern Southern Hemisphere Summer
margins under effect of Westerlies
Isotherms deviate to north over oceans and south over Isotherms are more or less parallel to latitudes
continents Variation in temperature is more gradual
Gulf Stream and North Atlantic Drift in the Northern Atlantic
Ocean isotherms shift poleward
JULY JULY
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Northern Hemisphere Summer Southern Hemisphere Winter
Isotherms deviate towards the pole over landmasses and Isotherms are more or less parallel to latitudes
towards equator over the sea Migrate towards equator over the landmasses
Highest range of temperature over East Siberia (~60°C)
Least range of temperature between 1520°C (~3°C)
Heat Budget
Earth on a whole does not accumulate or loose heat
Amount of heat received as insolation = Amount of heat lost through terrestrial radiation
Heat is the interaction of insolation with atmosphere
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Clouds reflect more than snow covered surfaces
Earth absorbs more than atmosphere
Radiation from earth into atmosphere and then into space
Temperature Inversion
When temperature increases with rise in temperature Negative Lapse Rate
Inversion is usually of short duration, but quite common
Cool Air is below warm air, with more cool air above the layer of warm air
Conditions
Long winter night outgoing radiation is greater than incoming radiation
Clear skies allow unobstructed escape of radiation
Still air prevent mixing of vertical levels
Heat of the day is radiated off during the night and by morning hours, earth is cooler than above (Radiation Inversion)
Inversion lasts for a few hours till the sun warms the earth
Such conditions exist in polar areas around the year
Leads to stability in lower layers of the atmosphere
Smoke and dust particles get collected beneath the inversion layer and spread horizontally to fill the lower strata of the
atmosphere Affects cloud formation, precipitation and visibility
Convective clouds cannot grow high enough to produce showers
Reduce diurnal temperature variations
Frontal Inversion
Cold air mass undercuts a warm air mass and lifts it aloft
More slope than other kind of inversions
Unstable and destroyed by weather changes
Marine Inversion
Airmass passing over large water body (ocean/sea) in spring gets cooled by conduction
Passes over to land and under the warm air mass above the land
Air Drainage
Phenomenon by which cold air in hills and mountains produced at night flows under the influence of gravity (almost like water)
down the slope to pile up in pockets and valley bottoms with warm air above
Air Drainage protects plants from frost damages
Economic Impact
Houses and agricultural farms are situated along the upper slopes to avoid cold and foggy valley bottoms
Less rainfall due to stable conditions
Frost affects vegetation in lower slopes
Dust particles and smoke do not disperse in valley bottoms
Lapse Rate
Change in temperature with gain in altitude
Positive when temperature decreases with elevation
Zero when temperature is constant with temperature
Negative when temperature increases with elevation Temperature Inversion
Environmental Lapse Rate LR of nonrising air affected by radiation, convection and condensation
Why does temperature fall with elevation?
Pressure decreases (P is directly proportional to T)
At higher elevations, concentration of GHG decrease heat absorption capacity decreases
Adiabatic Lapse Rate (ALR) —> Rate of Condensation —> Latent Heat of Condensation —> driving force behind convectional
rains/cyclones
ALR is governed by Gas Laws, around 6°C/km
Dry Adiabatic Lapse Rate
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Less moisture —> condensation during upliftment of air parcel is low —> latent heat of condensation released is low —> Fall in
temperature with height is greater compared to ALR
Associated with stable conditions, because it has less moisture
9.8°C/km
Wet Adiabatic Lapse Rate
More moisture —> Condensation during upliftment of air parcel is high —> latent heat of condensation released is high —> Fall
in temperature with height is lesser compared to ALR
Associated with unstable conditions, as it has more moisture
4°C/km
As an air parcel rises and cools, it may eventually lose moisture and lapse rate approaches the DALR
Difference between normal lapse rate and DALR and WALR determines the vertical stability in the atmosphere
Lapse rates can help predict type of cloud formation, incidence of thunderstorms, turbulence intensity
If ALR > DALR —> More stable than normal —> Little moisture in parcel —> No rains, Not enough heat of condensation is released,
the parcel of air cools down and falls to ground once it become denser
If ALR < WALR —> Less stable than normal —> More moisture in parcel —> Latent heat of condensation released can generate
thunderstorms
If WALR < ALR < DALR —> Enough moisture, conditional stability (depends on other factors)
Katabatic Wind Hot dry wind that blows down a mountain slope Falling parcel of air in which temperature changes happen
adiabatically
Temperature Anomaly Difference between mean temperature of a place and mean temperature of its parallel
Near the earth’s surface, temperature changes are mostly nonadiabatic because horizontal movements cause mixing of air and
modify its characteristics (radiation, conduction or mixing with cold air)
Nonadiabatic processes cannot produce substantial amount of precipitation
In higher layers of atmosphere, changes in temperature are due to expansion and compression only > Adiabatic (temperature
change through change in heat available per unit volume)
ATMOSPHERIC CIRCULATION
Air expands when heated and gets compressed when cooled —> Variations in atmospheric pressure
Atmospheric pressure determines direction of wind (HP —> LP) and whether air will rise or sink
Vertical variation in pressure is not uniform affected by density, gravity, amount of water vapour
Wind redistributes heat and moisture
Atmospheric pressure Weight of Column of air in unit area from mean sea level to top of atmosphere
Air at surface is denser and has higher pressure due to Gravity
Why we don’t experience strong upward winds?
Vertical pressure gradient is much larger than the horizontal pressure gradient balanced by a nearly equal but opposite gravitational
force
Horizontal Pressure Variations
Small differences in pressure affect wind direction and velocity
Isobars indicate horizontal pressure distribution
Spacing of isobars indicates rate and direction of pressure changes Close spacing means steep gradient (Low pressure
system lowest pressure at centre, High pressure system highest pressure at centre)
Pressure is calculated after being reduced to sea level, in order to account for effect of altitude on pressure
World Pressure Distribution
Pressure belts move with apparent movement of the Sun (northwards in summer, southwards in winter)
Amount of shift is less in Southern Hemisphere due to predominance of water
Doldrums
10° N/S Zone of convergence of trade winds from the two hemispheres (subtropical highs)
Equator LOW 0° Calm air movements no surface winds, only vertical currents are found
Thermal Low Position of the belt varies with apparent movement of the Sun
Most of this region lies along oceans —> vertical winds carrying moisture form cumulonimbus
clouds and lead to thunderstorms
Subtropical HIGH 30°N/S
Dynamic High High pressure due to subsidence
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After saturation at ITCZ, air moving away from equatorial ow pressure in upper troposphere
becomes dry and cold and subsides
Deserts are located in this region, as the subsiding air is warm and dry
Descending currents feed the wind moving towards adjoining low pressure belts
Tropical and extratropical cyclones
Not very well pronounced round the year due to low temperatures in these latitudes
Dynamically produced due to ascent of air as a result of convergence of westerlies and polar
easterlies
Subpolar LOW 60° N/S
Mainly over oceans
Dynamic Low
Area of contrast between cold and warm air masses produces polar jet streams
Due to contrast in temperature of winds from subtropical and polar regions, extra tropical
cyclones are produced
Polar HIGH 90°C N/S Cold air that converges and rises in sub polar LP belt, on reaching the poles becomes dry and
Thermal High subsides creating a high pressure belt
Pressure belts are formed by
Thermal Factors Heating and Cooling
Dynamic Factors Pressure gradient forces, apparent movement of Sun, Coriolis Force
Factors affecting Wind
Pressure Gradient Force
Strong where isobars are closer to each other (high rate of change of pressure per unit distance) —> higher wind speed
Wind direction is perpendicular to isobars
Frictional Force
Greatest at the surface an influence extends upto an elevation of 13km
Minimal over the sea
Over uneven terrain, due to high friction, the wind direction makes high angles with isobars and speed gets retarded
Coriolis Force
Generated due to rotation of earth about its axis Object is not actually moving beyond its course but appears so due to rotation
of the earth
Winds do not cross the isobars at right angles but get deflected (Right in N hemisphere, Left in S Hemisphere)
Zero at Equator and Maximum at Poles At higher latitudes, the speed of earth’s rotation is less, apparent deflection (Coriolis
force) is more
Greater the PGF, greater the wind velocity, greater the deflection
Acts perpendicular to Pressure gradient force
In LP areas, wind blows around it
At equator, wind blows perpendicular to isobars (No Coriolis Force) and the LP gets filled instead of getting intensified —> No
cyclones
Geostrophic Wind When isobars are straight and there is no friction, Pressure gradient force is balanced by Coriolis force and the
resultant wind flows parallel to the isobar
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Cyclonic Circulation Around low Anticlockwise in N hemisphere, Clockwise in S hemisphere
Anti Cyclonic Circulation Around high Clockwise in N hemisphere, Anticlockwise in N Hemisphere
Low pressure Air converges at surface and rises, diverging in upper layers
High pressure Air converges in upper layers and subsides from above, diverging in lower layers
General Circulation of Atmosphere
Pattern of planetary winds (which also sets in motion ocean water circulation) depends on
Latitudinal variation of atmospheric heating
Emergence of pressure belts
Migration of belts following apparent path of sun
Distribution of continents and oceans
Rotation of earth
Easterlies from tropics converge at ITCZ
Converged air rises upto heights of 14km in the troposphere and moves towards the poles where it converges
with the upper layer winds coming from Sub polar region
Hadley Cell
Part of accumulated air cools down, sinks to ground and forms a subtropical high and then move towards the
ITCZ to complete the cell
On the surface, the winds are easterlies
Cold air that rises at Sub Polar low moves towards the equator in upper layers and converges with upper
Ferrel Cell layer winds coming from the equator, cools down and sinks at SubTropical high
On the surface, the winds are Westerlies
Cold air that rises at Sub Polar low subsides at poles and moves back towards the subpolar low
Polar Cell
On the surface, the winds are easterlies
The winds in the upper layers of these cells are geostrophic they deflect greatly resulting in three different cells, instead of a single
cell where air rises at Equator and subsides at poles
Walker Cell
Generally, warm waters towards Indonesia and cold water on the Peruvian coast
Cell forms in which winds rise near Indonesia due to low pressure and subside off the Peru coast and then move towards
Indonesia to complete the Walker cell
Reversing of Walker Cell conditions leads to El Nino phenomenon —> Change of LP and HP points is called Southern
Oscialltion
Warm water of central Pacific Ocean slowly drifts towards SA coast and replaces the Peruvian current —> El Nino
Impact of El Nino
Arid coast of South America receives rainfall
Drought in Australia and Indonesia
Floods in China
Hurricanes and Tropical Storms in eastern Pacific
Rise in vector borne diseases
Jet Streams
Circumpolar
Narrow concentrated bands 50150km across
Meandering Depends on temperature gradient High temperature, less meandering When there is high temperature contrast,
jet stream flows in a straight line
Subpolar JS meanders more than Subtropical JS
Rossby waves Meandering Jet Streams are called Rossby Waves natural phenomenon in atmosphere and oceans due to
rotation (varying Coriolis Force)
When temperature contrast is low —> speed of jet stream is low —> Coriolis force is weak —> Meandering
Formed when polar air moves toward the Equator and tropical air is moving poleward
Their existence explains cyclones and anticyclones
Upper tropospheric Flow just below the Tropopause (Subtropical Jet at 1016km, Polar Jet at 69km) Subtropical Jet flows at
higher altitudes because the troposphere is thicker at the Equator
High velocity large due to less friction in upper layers
Faster in winter than in summer, The core of the jet stream travels faster
Geostrophic streams
Part of upper level westerlies
Jet Streams in Northern Hemisphere are more forceful due to greater temperature gradients
Jupiter and Saturn also have Jet Streams
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Permanent Jet Streams
Coriolis Force + Temperature contrast between tropical and subtropical regions
In the winter it is continuous in both hemispheres
Exists all year round in Southern Hemisphere
SubTropical Jet Stream
Intermittent in Northern Hemisphere during summer when it migrates north
STJ can be temporarily displaced when strong midlatitude troughs extend into subtropical latitudes
STJ and merge with PJ leading to cloudbursts
Produced by a temperature difference, closely related to polar front
Influences path, speed and intensity of temperate cyclones
Polar Jet Stream Influences climate of regions around 60° N/S
More variable position than subtropical jet
Summer shifts towards poles, Winter shifts towards equator
Temporary Jet Streams
High velocity wind in lower troposphere
Persistent in direction, position and intensity from June to October
Tropical Easterly Jet Induces secondary circulations that enhance convection over South India
Jet may be caused by uniquely high temperatures and heights over the Tibetan plateau
Upper level venting system for the SW monsoon
Most intense in June to August
Somali Jet Moves southward in the winter
Flows from southern Indian Ocean to central Arabian Sea
Significance of Jet Streams
Maintenance of latitudinal heat balance
Polar Jet influences mid latitude weather disturbances Severe storms when Jet Streams interact with surface winds
Influence path of temperate cyclones and distribution of precipitation
STJS, TEJ and Somali Jet influence Indian monsoons
Used by flights when in the same direction, avoided when in the opposite direction (Bumpy flight because Jet Streams can
cause sudden movements even when the weather is clear)
Role of Polar Jet
Separates colder air and warmer air
Push around air masses, moving weather systems to new areas
Determine path and intensity of frontal precipitation
Weak Polar Jet results in slipping of Polar Vortex into Temperate regions
Ridges and Troughs give rise to jet streaks
Wind leaving jet streaks are rapidly diverging, creating LP conditions near Tropopause
Air below rises up to replace them —> LP at the surface
Surrounding surface winds rush inwards —> Coriolis Force creates a cyclonic rotation around a central LP
Wind entering the jet streak are rapidly converging, creating HP conditions near Tropopause
Convergence leads to Divergence at the surface —> HP at surface
Winds flow out of this HP —> Coriolis Force creates an anticyclonic rotation around a central HP
Air Mass
Air the remains over a homogeneous area (ocean, plains) for a long time, and therefore acquires characteristics of that area
(Temperature, Humidity)
Little horizontal variations
Source regions Warm tropical and subtropical oceans, Subtropical hot deserts, Cold high altitude oceans, Cold snow covered
continents in high latitudes, permanently ice covered continents in Arctic and Antarctica
Should be extensive with gentle, divergent air circulation
Areas with high pressure, but little pressure gradient are ideal source regions
Source region establishes heat and moisture equilibrium with overlying airmass
No major source regions in mid latitudes as these regions are dominated by cyclonic and other disturbances
Extend from surface to lower stratosphere
Cold Air Mass Warm Air Mass
Colder than underlying surface Warmer than underlying surface
Instability and atmospheric turbulence Table weather conditions
Arctic Ocean, Siberia, North Canada, Southern Ocean Sahara Desert, Tropical Oceans
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Influence on Weather
Vertical temperature distribution (indicates stability and coldness/warmness) and Moisture content influence the weather
Carry moisture from oceans to continents and cause precipitation over landmasses
Transport latent heat
Migratory atmospheric disturbances like cyclones and storms originate at the contact zone between different air masses
Polar Tropical
Arctic Basin, North NA, Eurasia, Antarctica
Tropical and Subtropical deserts
Dry, cold, stable
Dry, hot, stable and do not extend beyond the
Continental Winters frigid, Clear, Stable
source
Summers Less stable, less anticyclonic
Dry throughout the year
winds
Oceans between 4060°
Oceans in tropics and subtropics Mexican Gulf,
Mostly continental polar air masses which
Pacific, Atlantic
have moved over to warmer oceans, got
Warm, humid, unstable
Maritime heated up and collected moisture
Winters Mild temperature, overcast skies with fog
Cool, moist, Unstable
Summer High temperature, high humidity, cumulus
Winters High Humidity, fog and precipitation
clouds, convectional rainfall
Summers Clear, Stable
Fronts
Front Boundary zone of meeting of two air masses
Feature of midlatitudes
Do not form in Tropics or Polar regions air masses converging in tropics or polar regions are not distinct in characteristics
(temperature, humidity)
Frontogenesis Process of formation of fronts cause of mid latitude cyclones
Northern Hemisphere in AntiClockwise direction
Southern Hemisphere in Clockwise direction
Characteristics
Temperature contrast affects thickness of front higher temperature contrast leads to thinner fronts
Steep Pressure gradient
Front experiences wind shift, as wind motion depends on Pressure gradient and Coriolis Force
Cloudiness and precipitation because of ascent of warm air which cools down adiabatically, condenses and causes rainfall
Surface position of the front does not change
Wind motion on both sides is parallel to the front
Stationary Front
Once the stationary boundary moves, it becomes warm or cold front
Cumulonimbus clouds are formed cyclones migrating along a stationary front can cause flooding
Cold airmass advances into warm air mass
Moves upto twice as quickly as warm front
Cold fronts are steeper than warm front
Heavy rains and thunderstorms in the warm sector
Cold Front Approach of cold front is marked by increased wind activity in the warm sector
Clouds —> cirrus, altocumulus, altostratus
At the front, nimbus and cumulonimbus cause heavy showers
Passes off quickly, but weather along it is violent
Frontolysis Cold airmass completely uplifts warm airmass
Warm air moves over cold air
Frontolysis Warm air completely moves over the cold air
Temperature and wind direction changes are gradual
Warm Front Moderate precipitation over a large area for a long time
No cumulonimbus clouds as gradient is gentle
Clouds —> Cirrus, Stratus, Nimbus
Cirrostratus clouds ahead of the warm front create a halo around sun and moon
Cold front of a rotating low pressure system catches the warm front, so that warm air is forced upwards
Cold airmass overtakes warm airmass and goes underneath it
Weather is a mixture of cold front type and warm front type
Occluded Front
Midlatitude cyclones involve formation of occluded fronts
Frontolysis When arm sector diminishes
Clouds typical of both cold and warm fronts on opposite sides of the occlusion
Tropical Cyclones
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Originate over oceans in tropical areas and move over to coastal areas causing heavy rainfall and storm surges
Irregular wind movements involving closed circulation of air around a low pressure system(rapid upward movement of hot air under
Coriolis Force)
Clock wise in northern hemisphere, Anticlockwise in Southern Hemisphere
Conditions for formation
Large sea surface with T > 27 °C release of latent heat of condensation drives the storm
On the east coast of continents, warm currents intensify the low pressure
Cyclones don’t form on west coast due to presence of cold currents
Depth of warm water should be 6070m so that surface temperature is not affected by mixing of waters due to convection
currents
During ElNino years, hurricanes occur in Eastern Pacific due to accumulation of warm waters
Coriolis force to create cyclonic vortex (No cyclones at equator)
Small variations in vertical wind speed
Preexisting weak low pressure area (due to small local differences in temperature of water and air)
Upper divergence over sealevel system ensures that rising air currents are pumped out and low pressure is maintained
Uniform wind speeds limits cyclone formation to equatorward direction of STJS (Temperate regions wind shear is high due to
westerlies)
Humidity helps in formation of cumulonimbusnimbus clouds
Why do cyclones occur in late summers?
Whirling motion is enhanced when doldrums are farthest from the equator
Happens during Autumn equinox due to high specific heat of water, oceans reach peak temperatures in August (continents in
June/July)
When ITCZ is farthest from equator, temperature difference of the converging air masses is maximum resulting instability is a
requisite for cyclones
Origin and Development
Early Stage
Thermal origin Develop over tropical sea during late summers local convectional currents acquire a whirling motion because
of Coriolis Force
Over warm oceans, air is uplifted a it becomes light
Lapse Rate Temperature falls moisture condenses
More warm air rushes to fill the space vacated by uplifted air and undergoes uplift and condensation
Due to excess moisture over the sea, air is sucked in which undergoes cyclonic circulation due to Coriolis Force
Air in the cyclonic vortex forms a region of calm around the centre Eye of the cyclone
Inner surface of the vortex forms the eye wall most violent region of the cyclone
When the moisture condenses, latent heat of condensation is released which further causes uplift of air
Mature Stage
Spiralling winds create multiple convective cells with successive calm and violent regions
Regions with cumulonimbus cloud formation are called rain bands
All wind that is carried upwards, loses its moisture and becomes cold and dense and descends through the cylindrical eye region
at the edges of the cyclone
Cloud formation is dense at the centre cloud size decreases from centre to periphery
Lateral Structure
Centre of tropical cyclone Roughly circular area of comparatively light winds and fair weather
Region of calm with subsiding air warm temperatures are due to adiabatic warming of the subsiding air
Eye Sinking air in the eye does not reach surface of the sea
Little or no precipitation
Region of lowest surface pressure and highest temperature in the upper layers
Eye is surrounded by eye wall
Strong spiralling ascent of air to greater heights
Eye Wall
Area of highest surface winds and torrential rainfall
From the eye wall, rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift out
Seem to spiral into the centre
Spiral Bands Warm moist air converges at the surface, ascends through these bands, diverges higher up and descends on
both sides of the bands
As the air subsides, adiabatic warming takes place and the air dries
Vertical Structure
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Inflow Layer Drives the cyclone
Middle Layer 37 km main cyclonic storm takes place
Outflow Layer Anticyclonic movement of air
Local Names
Indian Ocean Cyclone
Atlantic Hurricanes
Western Pacific and South China Sea Typhoons
Western Australia Willy Willy
Features
Symmetrical elliptical shapes with steep pressure gradients
Wind velocity in a tropical cyclone is more in poleward margins than at centre
Wind velocity is more over oceans than over land
Follow a parabolic path, their axis being parallel to isobars
Start with a westward movement, but turn northward after crossing 20°N (recurving)
Coriolis force, easterlies, westerlies affect path of a cyclone
Die beyond 30° latitudes due to cooler ocean water and wind shear due to westerlies
How can cyclones be monitored? Monitoring of pressure falls and wind velocities
Stations on islands in the ocean, coastal radars, weather radar on aircrafts, Satellite Monitoring using high resolution radiometers
(visual and IR regions of the spectrum)
Storm Surge
Abnormal rise in sea level as the cyclone crosses the coast leading to sea water inundation the coastal strip
Results in increased salinity of the inundated area making the land unfit for agricultural use for a few seasons
Depends on intensity of cyclone (maximum winds and lowest pressure facilitates), coastal bathymetry (shallow coastline leads to
higher surges) and if the landfall coincides with high tide
Storm Tide = Storm Surge + Astronomical Tide
Impact of Cyclones/Storm Surges/Torrential Rainfall
Erosion of beaches and embankments reduces fertility of coastal plains
Torrential rains lead to flash floods
Loss of life and property due to rains, winds and surges
Damage to standing crops
Pollution of drinking water sources and contamination of ground water
Outbreak of diseases
Why more cyclones over Bay of Bengal than in Arabian Sea?
Bay of Bengal cyclones originate insitu or as remnants of Typhoons from Western Pacific (quite high, due to which more
cyclones in BoB)
Arabian Sea cyclones originate insitu or as remnants of cyclones from BoB, as cyclones from BoB weaken after landfall, few
pass into Arabian Sea
Arabian Sea has lower temperature than BoB
In SW monsoon season, cyclones don’t develop
Monsoon winds in lower troposphere and Tej in upper troposphere lead to large vertical wind shear
Low pressure depressions form in North Bay of Bengal close to the monsoon trough due to presence of land, they have short
oceanic stay (quick landfall) and don’t develop into cyclones
Naming of Cyclones
Ease of communication between authorities and to public, Avoid confusion between multiple cyclones that may occur at the
same time at close geographical locations
WMO has divided world oceans into basins and assigned responsibility of naming cyclones to local bodies
North Indian Ocean region Arranged by alphabetical order of country who has named the cyclone
5% of global cyclones in Indian Ocean (BoB:Arabian = 4:1)
Polar Cyclones
Arctic and Antarctic most frequently over Northern Russia and Siberia
Not seasonal can occur anytime of the year
Can last from a day to several weeks (tropical cyclones don’t last more than a day)
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Central Dense Overcast Cirrus Cloud Shield that results from the thunderstorms in the eyeball of a tropical cyclone
IMD 4 stage Tropical Cyclone warning system
PreCyclone Watch Issued when there is a depression over BoB irrespective of the distance from coast, 72h before adverse
weather
Cyclone Alert (Yellow) When cyclone is beyond 500km of the coast, 48h before adverse weather
Cyclone warning (Orange) When cyclone is within 500km of the coast, 24h before adverse weather, time/place of landfall are
mentioned
Post landfall Outlook (Red) When cyclone is within 200km, 12h before landfall
Extra Tropical Cyclone
Formation
Form along polar front Involves mainly an occluded front
Initially the front is stationary
In the Northern Hemisphere Warm air blows from south and cold air from north of the front
Sets in motion an anticlockwise cyclonic circulation
Pockets of warm air are wedged between forward and rear cold air
Warm air glides over the cold air clouds appear over the sky ahead of the warm front and cause precipitation
Cold air approaches from behind and pushes the warm air up cumulus clouds along the cold front
Cold front moves faster than warm front, lifting it up —> Cyclone dissipates
Occur in USA and Canada, belt from Iceland to Barents Sea, Siberia, Baltic Sea, Mediterranean Sea, Antarctic Frontal Zone
Fujlwara Two cyclones move towards each other and rotate around one another, with the smaller and less intense one moving more
quickly
Tropical Cyclones Extra Tropical Cyclones
1030°N/S 3565°N/S
Originate mostly in late summers Irregular but more in winters
Inverted V shaped, Lower height than Tropical Cyclones (8
Elliptical shape, Higher (upto 14km)
11km)
Low Pressure System Clear Frontal System
Originate only over the sea Originate over both land and sea
Cover a smaller area (100500km) Cover a much larger area (3002000km)
Temperature at the centre is almost equally distributed Sectors of the cyclone have different temperatures
Interaction with upper level air flow not well characterised Distinct interaction with upper level air flow (Jet streams)
More intense rains and wind velocity over a short time Less intense rainfall, less wind velocity but over a longer time
No rainfall in the eye Rainfall occurs all over the front
Move West to East
Move East to West
Move along with Westerlies
Fewer varieties of clouds Variety of cloud development at different elevations
Not associated with surface anticyclones Suceeded and proceeded by surface anticyclones
Damage is more Damage is much lesser
Winds cause more damage than flooding Flooding causes major damage
Beneficial as it generates Western Disturbances brought by
Both coasts are affected, but east coast is affected more
STJS to India
Polar Vortex
Large pocket of very cold air which sits over the polar region during the Winter season (gets weaker in the summer)
Upper tropospheric, sometimes extending into lower stratosphere
Circumpolar and rotates anticlockwise surrounds polar high and lies within the polar front
Closely associated with jet streams which prevents it from spilling southwards
Polar Vortex will remain in its place when westerlies and polar jet are strong (huge temperature contrast between temperate and
polar regions)
When Polar Jet is meandering due to low temperature contrast (not necessarily in summer), polar vortex intrudes into mid
latitude regions leading to significant cold outbreaks
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During winter in the Northern Hemisphere, the polar vortex will become less stable, sending cold Arctic air southward over the
United States
Primary/Prevailing Winds
Subtropical HP —> Equatorial LP
Descending and stable in their areas of origin
Trade Winds
Pick up moisture as they move towards the equator
NE and SE trade winds from the two hemispheres meet at Equator, rise up and cause heavy rainfall
Subtropical HP —> Sub Polar LP
Westerlies of Southern Hemisphere are stronger and more persistent due to vast expanse of water (4065°S)
Westerlies
Poleward boundary for westerlies is highly fluctuating
Produce wet spells and variability in weather
Polar Easterlies Polar HP —> Sub Polar LP
Secondary/Periodic Winds
Large scale modification of planetary wind system
Due to northward migration of ITCZ in summer, the SE trade winds get modified into SW winds
Monsoon After picking up moisture, they cause rainfall over Asian landmass
In winter, the ITCZ moves south of equator, generating NE monsoons
In countries like China and Japan, NE monsoon is stronger than SW monsoon
Day time Land hotter than sea Sea to Land —> Sea Breeze
Land/Sea Breeze
Night time Sea hotter than land Land to Sea —> Land Breeze
Day time Mountain tops are hotter than valleys Valley to Mountain —> Valley Breeze
Night time Slopes cool down and cool air descends into the valley —> Mountain breeze
Mountain/Valley Breeze Cool air of high plateaus and ice fields draining into the valley is called KATABATIC WIND
Another type of warm wind occurs on the leeward side Moisture in these winds while crossing the
mountain ranges condense and precipitate, and when it descends the dry wind gets warmed up by
adiabatic process and can melt snow
Local Winds
MayJune, usually in afternoons
Loo India/Pakistan Blows from the west
Harmful Wind 4550° C
Rainfall on windward side, dry on the leeward side 1520° C
Foehn Alps
Useful helps animal grazing by melting snow, aids ripening of grapes
West slope of Rockies
Chinook Rockies
Useful Keeps grasslands clear of snow in winter
Alps towards
Mistral Mediterranean Sea Very cold and dry with high speed, Blizzards in South France
through France
Sahara to Reaches hurricane speeds in North Africa and South Europe
Sirocco
Mediterranean Dusty dry conditions in North Africa, storms in Mediterranean
Pampero Argentina Chinook Rockies
Gregale Mediterranean Foehn Alps
Bora Hungary/Italy Khamsin Egypt
Tramontane Europe Harmattan West Africa
Southerly Buster Australia Santa Ana California
Punas West Andes Kala Burun Central Asia
Blizzard Tundra Brickfelder Australia
Purga Russia Zonda East Andes/Argentina
Levanter Spain Sirocco Sahara to Mediterranean
Ghibli Libya
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Levacci Spain
OZONE DEPLETION
Balance between formation and degradation of ozone (action of UV rays on oxygen) for maintaining an Ozone layer
Halocarbons shift the equilibrium towards degradation of Ozone injected into the stratosphere through tropical cumulus clouds
Largest decrease in stratospheric ozone around earth’s polar regions
Dobson Units Thickness of Ozone in a column of air from ground to top of atmosphere
Photodissociation of Ozone Depleting substances like Halocarbons —> Free Chlorine atoms (or other halogens)
Cl + O3 —> O2 + ClO
ClO + O3 —> Cl + 2 O2 ————> Chlorine is freed to act on another molecule of Ozone making this a cycle
Polar Stratospheric Clouds
Nacreous Clouds
Form in frigid regions of lower stratosphere (1525 km) well above tropospheric clouds
Mostly seen in winter at high latitudes Scandinavia, Iceland, Alaska, North Canada
Contain water, Nitric acid and/or sulphuric acid
Formed during Polar Vortex, more so in the South Pole (Polar Vortex is a polar cyclone closely associated with jet streams. It is
formed in winter and gets weaker in the summer. Surrounds the polar highs and lies within the Polar Front)
Convert reservoir compounds like CFCs into ClO and Cl (reactive free radicals) by providing a surface —> accelerate ozone
depletion
Remove nitrogen which otherwise moderates the destruction of Ozone by Chlorine
El Nino
Warm surface waters along the coast of Peru and Chile, replacing the cold Humboldt current
Upwelling of cold, nutrient rich deep ocean water is reduced
Normal Year LP near Australia, HP near Peru —> Strong trade winds move from east to west —> Carries warm surface waters
westwards, bringing convective storms to Indonesia and causes upwelling of nutrient rich water near Peru coast
El Nino year LP in central Pacific —> weak HP in West Pacific leading to weak Walker cell (Walker cell might even get reversed) —>
equatorial counter current accumulates warm ocean water along coastlines of Peru —> Thermocline drops which cuts off upwelling
Effects of El Nino
Drought to Western Pacific Australia, Indonesia, India
Rains to west coast of South America and East Pacific
Convective Storms and hurricanes in Central Pacific
Detrimental effect on marine life
El Nino reduces strength of Indian Monsoon droughts in India have been El Nino years (except when there is Indian Ocean
Dipole)
Southern Oscillation
Only El Nino Warm water in Eastern Pacific + Cold water in Western Pacific
Only SO Low Pressure in Eastern Pacific + High pressure in Western Pacific —> Oscillation of pressures (Circulation in Walker Cell)
Period varies from 25 years
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Location of LP and rising limb of Walker cell over Western Pacific is favourable to Indian monsoons
Shifting eastward in El Nino years, reduces monsoon rainfall
Positive SO Tahiti HP, Darwin LP
SO Index = P (Tahiti) P (Darwin)
Indian Ocean Dipole
Difference in sea surface temperature between Arabian Sea and Eastern Indian Ocean
Positive IOD Arabian Sea LP, Eastern Indian Ocean HP Winds east to west favourable for monsoons in India
Negative IOD Arabian Sea HP, Eastern Indian ocean LP Winds west to east Indonesia is rainier, Monsoons are weakened
The two poles of IOD independently and cumulatively affect the quantity of rains for the monsoon
El Nino Modoki
Strong heating in Central Pacific and cooling in eastern and western Pacific
Results in two cell walker Circulation wet region in central Pacific
La Nina
Trade winds become extremely strong and abnormal accumulation of cold water occurs in central and eastern Pacific
Caused hurricanes in Atlantic
Drought in central North America
Abnormally heavy monsoons in India and SE Asia
Winter drought in Southern USA
Cold winter in Western Canada and NW USA
Wet weather in east Australia and south east Africa
WATER IN ATMOSPHERE
HUMIDITY
Water Vapour in air is Humidity
Absolute Humidity
Actual amount of water vapour present in atmosphere
Weight of water vapour per unit volume of air g/cubic m
Ability to hold air depends entirely on temperature warmer air can hold more humidity
Relative Humidity
Percentage of water vapour present compared to full capacity at a given temperature
Greater over oceans, least over continents
For a given parcel of unsaturated air, increase in temperature reduces relative humidity (maximum capacity increases while
absolute amount stays the same)
Gain in water vapour increases relative humidity
Decrease in temperature causes decrease in absolute humidity but increase in relative humidity
Determines rate and amount of evaporation
Relative humidity of saturated air is 100%
Specific Humidity
Weight of water vapour per unit weight of air (g/kg)
Constant doesn’t change with pressure or temperature (AH and RH are variable)
Factors affecting evaporation
Temperature Higher temperature —> Lower RH —> More evaporation
Relative Humidity
Air movement/Wind Speed
Air Pressure Lower Pressure helps in evaporation
Salinity Inversely proportional
Area of evaporating surface large SA more evaporation
When does condensation take place?
Temperature is reduced to dew point with volume remaining constant
Both volume and temperature are reduced
Moisture is added through evaporation
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Dew Point Temperature at which saturation occurs for a given parcel of air
Dew
Moisture deposited as water droplets on cooler surfaces of solids
Dew Point > Freezing Point
Ideal conditions clear sky, calm air, high RH, cold and long nights
Frost
Moisture deposited as ice crystals
Dew Point < Freezing Point
Ideal conditions clear sky, calm air, high RH, cold and long nights
Fog
Temperature of an airmass containing large amount of water vapour falls all of a sudden, condensation takes place within itself
on dust particles
Fog is equivalent to a cloud with its base very near to the ground
Smoke provides nuclei that help in formation of fog, Smoke + Fog = Smog
Radiation Fog Radiation of heat from ground coming in contact with adjacent air Not very thick
Advection Fog warm air moves horizontally over a cold surface Thick and persistent occurs in oceans where warm and cold
waters mix
Frontal/Precipitation Fog Precipitation in warm air mass condenses to form fog at boundary of two air masses
Mist
Similar to fog, but has much more moisture
Each hygroscopic nuclei contains a thicker layer of moisture
Frequent on mountain slopes where rising warm air meets a cold surface
Visibility is greater in mist than in fog
Haze
Dust. Smoke and other dry particles obscure the clarity of the sky
No condensation (similar to smog in other respects)
Clouds
Clouds are masses of minute water droplets or tiny crystals of ice formed by condensation of water vapour in free air at high
elevations
Feathery Thin and detached
Cirrus 812 km White
appearance Composed of ice crystals
Layered formed due to loss of heat or mixing of
Stratus Across layers
air masses of different temperatures
Mid levels or
Extremely dense and opaque to rays of sun
Nimbus close to Black/Gray
Shapeless masses of thick vapour
surface
Low Clouds Stratus, Cumulus, Nimbostratus, Cumulonimbus, Stratocumulus
Middle Clouds Altostratus, Altocumulus
High Clouds Cirrus, Cirrostratus, Cirrocumulus
Extensive vertical development Cumulus, Sumulonimbus
Smog
Caused by burning of coal, vehicular emissions, industrial fumes
Smog is a secondary pollutant
Primary pollutant pollutant emitted from a source Methane, Carbon dioxide
Secondary pollutant pollutant formed due to reactions of two substances Ozone
Sulphurous Smog Photochemical Smog
London Smog (Delhi smog is also sulphurous) Los Angeles Smog
Reducing Smog Oxidising smog
Caused due to high concentration of sulphur oxides as a result of Caused due to nitrogen oxides pollution due to large number of
fossil fuel combustion automobiles
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Reduced visibility, plant damage, eye irritation
Nitrogen oxides and organic compounds act in presence of
sunlight —> Ozone is formed
Aggravated by dampness and SPM in air
NO + VOC —> NO2
NO2 + UV —> NO + O
O + O2 —> O3
Effects of smog
Atmospheric pollution is increased by inversion that traps pollution close to the ground
Highly toxic illness and death
Reduces precipitation
Reduced visibility
Why is Smog issue in Delhi more than cities of comparable industrial capacity?
Continentality way from coast
Short duration of monsoon
Straw burning in nearby states
Cold temperature leading to temperature inversion
Higher number of automobiles
Combustion of oil, coal, gas
Lightning NO2 can suppress plant growth
NO/NO2
Forest fires and Volcanos Decreased visibility
Bacterial action in soil
Eye irritation and Respiratory irritation
Evaporation of fuels
VOCs Haze
Incomplete combustion of fossil fuels
Carcinogenic
Decreased crop yields, retards plant growth
Photolysis of NO2
Ozone Damages plastics
Stratospheric ozone intrusions
Breaks down rubber
Eye irritation
PAN NP2 + VOCs High toxicity to plants
Damage proteins
PRECIPITATION
Condensation causes condensed particles to grow in size. When resistance of air fails to hold them against the force of gravity, they
fall to the earth’s surface as precipitation (Precipitation is release of moisture after condensation of water vapour)
Sleet
Frozen raindrops and refrozen melted snowwater
When a layer of air with temperature above freezing point overlies a sub freezing layer near the ground, precipitation is in form of
sleet
Raindrops leave the warmer air and encounter colder air below as form pellets of ice
Hailstones
Several concentric layers of ice one over the other
Drops of rain are solidified into solid round pieces of ice
Virage Raindrops evaporate before reaching the earth while passing through dry air
Drizzle Light rainfall with drop size < 0.5mm
Snowfall Temp < 0° C, precipitation as fine flakes of snow
Mist Rain evaporates before reaching the ground leading to foggy weather
Types of Rainfall
Air on being heated becomes light and rises up in convection currents —> Condensation —> cumulus
clouds
Condensation in upper layers releases latent heat of condensation, which further heats the airmass and
Convectional Rain
causes it to rise further
Heavy rains, thunder and lightning does not last long
Common in equator and interior parts of continents especially northern hemisphere
Orographic Rain Saturated air mass comes across mountain —> Rises along the slope —> expands, temperature falls —
> Rainfall
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After rains on windward slope, winds reach the leeward slope and descend —> temperature rises and
capacity to carry moisture increases —> Less rain (rain shadow area)
Windward slopes have Cumulus clouds, leeward slopes have stratus clouds
Patagonia is a rain shadow desert
When two air masses with different temperatures meet, turbulent conditions are produced
Frontal Rain
Along the front, convection occurs and causes precipitation
World Distribution
Rainfall decreases from equator towards poles
Coasts receive more rainfall than interiors
Rainfall is more over oceans than on landmasses
Where westerlies are formed in areas under Ferrell cell, rainfall decreases from western margins towards interior
In the regions, rainfall is more on the east
Thunderstorm
Severe local storms of localised nature, occurring over a small area
Thunder storm is a well developed cumulonimbusnimbus cloud, caused by intense convection on hot moist days
If the could extends to heights of subzero temperature, hailstorms are formed
Insufficient moisture —> Dust storms
Potential + Heat energy —> Kinetic Energy
Thunderstorm is characterised by intense updraft of rising warm air, which causes clouds to grow bigger and rise to bigger heights
Mostly on ground due to higher temperatures, less frequent on water bodies due to lower temperature
Formation of Thunderstorm
Cumulus stage Ground heated by insolation —> LP due to rising air —> Air from surroundings rushes in —> Intense
convection of moist hot air builds up a cumulonimbus cloud
Mature stage Intense updraft of rising warm air —> Clouds grow bigger and rise to greater heights —> Downdraft brings down
rain —> Updraft and downdraft determine the path of the thunderstorm which at most times is erratic
Dissipating Stage Mostly dissipates in a few minutes
Motion of thunderstorm is due to interaction of updrafts and downdrafts, making it erratic
Down drafts are called microbursts and macrobursts dangerous for air crafts during take off and landing
Factors that cause thunderstorms High temperature/humidity, Condensation, Orography, Vertical Wind
Tornado
From the thunderstorm, spiralling wind descends with very low pressure at the centre (generally in mid latitudes)
Violently rotating air developed within a convective cloud and in contact with the ground
Water spouts Tornados over sea (weaker than tornados on land)
All continents except Antarctica
US and Canada have most number of tornados
Bangladesh is highly prone in Asia
Types of Thunderstorms
Thermal thunderstorm Intense heating of ground in summer
Orographic thunderstorm Forceful upliftment of warm, moist air when it passes over a mountain barrier —> cumulonimbus
cloud —> Windward side rainfall Common in JK, Meghalaya (Cherapunjee, Mawsynram)
Singlecell thunderstorm Small, brief, weak storms driven by heating on a summer afternoon Mango Showers and Blossom
Showers
Multicell thunderstorm new updrafts form along the leading edge of raincooled air (gust front)
Supercell thunderstorm Long lived highly organised storm due to an updraft that is tilted and rotating large and violent
tornados
Cloudburst = Intense torrential rainfall drought by a thunderstorm, mostly happens when an air mass with high humidity is stuck at a
place
Lightning
Water moves upward in the cumulonimbus cloud
Decreasing temperatures cause it to condense
Latent heat of condensation is released
Heat pushes the water further up
Move into sub zero layers and water droplets change into ice crystals
Smaller ice crystals move up, while bigger ice crystals come down
Resulting collisions trigger the release of electrons
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Moving free electrons cause more collisions and more electrons and a chain reaction ensues
Top layer is positively charged and middle layer is negatively charged
Current flows between the two layers, heating the air column
Heated air column expands and produces shock waves that result in thunder
Lightning from cloud to earth
Earth is electrically neutral —> compared to middle layer of the cloud, it becomes positively charged and a flow of current is directed
towards earth
Travelling through air (bad conductor of electricity) electrons try to find a better conductor and shortest way to the earth —> hit taller
objects on earth
2/3 of lightning activity happens within the clouds themselves
Most lightning activity on earth is seen near Lake Maracaibo
The lake is surrounded by swampy plains and enclosed on three sides by high mountains
The heat and moisture from swampy marshes creates electrical charges and as the air is destabilised at mountain faces, thunder is
produced
Impact of thunderstorms: Heavy rains —> Flash flooding, Lightning —> Fires, fatalities, Hailstones damage life and property
CLIMATE REGIONS
Genetic Classification Explain causes
Empirical classification Based on observed data (Koeppen)
Koeppen Classification Selected certain values of temperature and precipitation and related them to distribution of vegetation
Empirical classification based on mean annual and mean monthly temperature and precipitation data
Five major climate groups 4 temperature (A, C, D, E humid climates), 1 precipitation (B)
A Tropical Humid
Between Tropic of Cancer and Tropic of Capricorn
Sun overhead throughout the year + ITCZ = hot and humid climate
High annual rainfall, Low annual range of temperature
Tropical Wet (Af) Amazon basin, Climate
Western equatorial
Africa, East Indies Maritime tropical air masses
Temperature is uniform throughout the year (mean monthly temperature 27°C with
very little variation)
No demarcated seasons but maximum weather changes
Cloudiness, Heavy rainfall and land/sea breezes moderate the temperature
Diurnal and annual ranges of temperature are low
No dry season
Double rainfall peaks coinciding with equinoxes least rainfall occurs in June and
December
Convectional air currents leading to heavy rainfall in afternoons
Cumulonimbus clouds dark thunderstorms Equatorial regions receive less
insolation due to dense cloud cover
Vegetation
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7% of world forest area, 50% of forest cover
Tropical evergreen forests, dense canopy and large biodiversity
Selvas Amazon rainforests
Hardwood trees like mahogany and ebony, Mangrove forests in coastal areas and
brackish waters
Undergrowth is not dense as the canopy does not allow penetration of sunlight
Epiphytes (plants that grow harmlessly on another plant
Economy
Sparsely populated
Most primitive people live as hunter gatherers and some practice shifting
agriculture
Due to heavy rains, nutrients get washed away soils are not fertile
Java is an exception due to rich volcanic ashes
Lalang and thick undergrowth spring up when forests are cut and choke
rainforests
Inspite of many commercial species for timber, commercial exploitation is difficult
Mixed stands, hardwoods are hard to cut and don’t float in water making
transportation difficult, dense forests are difficult to access, no local market
Under colonial rule, plantation agriculture was introduced Best suited for
plantation agriculture because of high humidity and rainfall, cheap labour, good
markets in Europe and North America
Palm Oil Malaysia, Indonesia, Philippines
Rubber Brazil, Malaysia, Indonesia
Coffee Brazil
West Africa Cocoa West Africa
Sugarcane Brazil, Indonesia
Harbour important minerals like gold, copper, diamonds, oil and gas deposits
TseTse flies cause Ngana disease
Tribes
Pygymy Congo gather nuts
Dayak Borneo
Semang, Orang Malaysia
Hulli Africa
Vedda Sri Lanka
Yano Mami PNG
Indians Amazon collect rubber
Why are these regions not developed?
Construction and maintenance of infrastructure through dense forests is difficult
Excessive heat and high humidity creates physical handicaps conducive for
many diseases
Poor fertility of top soil + agricultural diseases
Tall and coarse grass which is not nutritious for livestock cattle meat and milk
yield is lesser than in temperate regions
Tropical Marine Climate
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Found outside the monsoon zone
Central America, West Indies, NE Australia, East Africa, Madagascar, East Brazil,
SE Asia
Rainfall is both orographic and convectional
Favourable climate for habitation but prone to severe tropical cyclones
Vegetation
Deciduous vegetation (both dry and moist) marked dry period during which trees
shed their leaves
More open, Less biodiversity compared to Tropical Wet forests
Shortage of rainfall causes transition to thorny scrubland and savannah with
scattered trees
Monsoonal vegetation is highly varied
Teak, Sal, Neem, Mango, Eucalyptus, Sal
Economy
High population density, but most of these regions are developing or
underdeveloped
Farming mostly of subsistence type, but intensive cultivation in regions with
irrigation
Shifting cultivation in NE India and SE Asia first crop may be bountiful but
subsequent harvests deteriorate as nutrients are exhausted
Livestock industry not as profitable as in temperate regions
Food Crops Rice, Wheat, Maize, Millet
Cash Crops 2/3 of sugar production from Tropical countries, Jute in Ganga
Brahmaputra delta, cotton in Indian subcontinent
Plantation crops Tea, Coffee (eastern slopes of Brazil) need moderate
temperatures, heavy rainfall and well drained highland slopes
Lumbering Teak in Burma accounts for 3/4 of world production (poisoned before
felling, so that the tree is dry and light enough to be floated down rivers Irrawady
and Chindwin) durable timber used in shipbuilding and construction purposes
Teak is valuable because strong, durable, immune from shrinkage, insects and
fungus
Shifting Cultivation
Malaysia Lacking
Burma Taungya
Thailand Tamrai
Philippines Caingin
Java Humah
Sri Lanka Chena
Africa/Central America Milpa
NE India Jhum
African Savannah Belt across W Africa to Sudan, curves southward into East
Africa and South Africa
Kalahari desert is a variant of Savannah climate
South American Savannah Llanos in Venezuela (north of equator), Campos and
Cerrado in Brazil (south of equator)
Dry parts of Cerrados/Sertao are called Catingas
Australian Savannah South of the strip of monsoon climate
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Indian Savannah North Karnataka, Southern Maharashtra and Telangana Asian
savannah is not true savannah due to monsoons
Vegetation
Tall grass (low in nutrition) and short trees Parkland landscape (Temperate
grasslands have short grasses)
Forest fires are a part of Savanna ecology exacerbated by Climate change
Trees are deciduous, with water storing mechanisms to survive periods of drought
Elephant grass tall and coarse
Savannah merge into thorn forests on the drier margins
'Big game' country
Economy
Not good for agriculture poor lateritic soil
Rainy season, torrential downpours cause leaching
Dry season intense heat dries up the moisture
Pastoralism is prevalent (natural cattle country) agriculture is barely practiced
Quality of grass does not allow large scale ranching
But with technological advancement, Queensland is now largest milk and meat
producing state in Australia
Droughts due to unreliable rainfall
Plantation crops Cotton, Sugarcane, Coffee
Sahel region was prosperous in the past but now faces economic and agricultural
crisis
Sahel is a cultural divide in Africa
Political instability hinders development in Africa (Boko Haram, etc.)
Tribes
Masai Kenya and Tanzania pastoralists
Kikuyu Kenya
Hausa Nigeria Muslim dominated settled cultivators
Ibo Nigeria Boko Haram
Bushmen, Khosian, Hottentot Kalahari
B Desert Climate
Characterised by very low rainfall not adequate for the growth of plants
Low latitudes Subtropical high regions where subsidence leads to less rains
Western margins of continents extend more equator wards and occur on coast land
3560° N/S interior of continents where maritime humid winds do not reach
Formation of deserts
Subtropical high pressure belts Descending air with high temperature with divergence at surface
Cold currents HP = no disturbances = no rains
Off shore trade winds have lost their moisture by the time they reach the coast
Rain Shadow Rains on windward side, when wind moves to leeward side, they move down warming up and do not shed
moisture
Continentality Rain bearing winds have lost moisture by the time they reach interior of continents
Hot Desert Sahara Offshore trade winds and cold current = high pressure = no rainfall
Climate Great Westerlies that are on shore blow outside desert limits
Sub Australian
tropical Desert Atacama Desert Peru Current
Desert Arabian Sahara Desert Canary Current
BWh Desert Namib Desert Benguela Current
Iranian Great Australian Desert West Australian Current
Desert California Desert California Current
Thar
Desert Sahara Desert extends across Middle East
Kalahari Thar desert extension of Sahara desert and sand carried from Gobi and Mongolia
Desert Israel Desert Negeve Greenest desert due to microirrigation
Namib
Desert Sandy Desert Erg Arabian Desert
Mojave, Rocky Desert Hamada Great Victoria Desert
Sonoran, Stony Desert Reg Namib
California, Iran DashteLut, DashteKavir
Mexican
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Climate
Rainfall as violent thunderstorms of convectional type may cause flash floods
Rainfall is highly variable and not enough to build soil moisture
No cold season
Fog is common on coasts bordering cold currents
Tribes
Tuareg Morcco/Libya 'blue tribe' nomadic herding
Bindibu Australia Hunter/gatherer
Rainless due to continentality and rain shadow effect
Continentality Gobi Desert
Rain shadow effect Patagonian Desert (rain shadow of Andes)
Climate
Rainfall as violent thunderstorms of convectional type may cause flash floods
Rainfall is highly variable and not enough to build soil moisture
Midlatitude deserts have higher diurnal range of temperature compared to hot deserts —> Due to
continentality
Occasionally, depressions may penetrate the Asiatic landmass causing light rains in winter
Gobi Severe winters strong cold winds When ice thaws in summer, floods are caused
desert
Patagonian
Tribes
desert
Ladakh, Bedouins Arabs Nomadic herding
Mid Kyzl Kum, Mongols Gobi Nomadic herding
latitude Turkestan, Bushmen Kalahari hunter/gatherer
Desert Takla
Sub Makan
tropical Vegetation
Steppe
BSh Kyzlkum Xerophytic and droughtresistant
Doab Cacti, Thorny bushes, wiry grasses, scattered dwarf acacias
between Trees are rare but date palms grow where water is available
Amu Darya Intense evaporation increases salinity of soil leading to formation of hard salt pans Baladas and
and San Playas
Daryl Seeds have thick, tough skins to protect them
Foliage is wait/hairy/needle shaped to reduce loss of moisture
Economy
Settlements around rivers Nile, Indus, TigrisEuphrates, Colorado
Oases support vegetation and habitation (Tafilalet Oasis Morocco)
Gold in Australian Desert Kalgoorlie
Diamonds in Kalahari desert
Caliche (source of sodium nitrate) and Copper in Atacama
Oil in Saharan and Arabian deserts
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latitude continents Pustaz Hungary black soil (chernozem)
Steppe In the Prairies North America wheat granaries, ranching
Temperate Westerly Pampas Argentina and Uruguay ranching, wheat
Grassland belt Veld South Africa maize, cattle rearing
Downs Australia Merino sheep
Canterbury NZ
Gulmarg, Sonmarg are temperate grasslands due to altitude
Climate
Continental climate with extremes of temperature
In Southern Hemisphere it is less extreme and more rains due to maritime influence
Heaviest rains in late spring and early summer
Chinook ascends the Rockies and descends into Prairies melts snow in pastures
Vegetation
Treeless because rain bearing winds don’t reach the interior of continents
Grasses are much shorter and more nutritious than in Tropical grasslands
Growth of grasses is not abruptly checked by summer droughts or winter cold
Increase in precipitation polewards leads to a transitional zone of wooden steppes
Not much animal diversity, but horses are found
Economy
Extensive, mechanised wheat cultivation Granaries of the world (Also maize)
Level relief makes them easy for ploughing and harvesting
Tufted grasses replaced by Lucerne or Alfalfa for cattle ranching
Collective farms and state farms
Earlier, tribes like Kazakhs and Kirghiz practised nomadic herding now replaced by communist
economy
Export large amount of beef, wool, hides
C Warm Temperate Climates
Eastern and Western Margins of continents between 3050° C
Warm summers and mild winters
Mediterranean Around Mediterranean Climate
Climate California
Cs Vale of Chile Caused due to shifting of wind belts
SW tip of Africa Climate is not extreme due to cooling effect of water bodies
Clear skies and high temperatures
Western margin of Hot, dry summers and cool, wet winters
continents 3045°N/S Summer Westerlies are off shore no rains strong winds from inland
desert may cause wildfires
Winters Westerlies are onshore (LP shifts towards equator due to cooling)
downpours are infrequent but torrential
Local Winds
Sirocco Hot “Blood rain” (red dust of Sahara), Sahara to Mediterranean
Mistral Cold velocity intensified by funnelling between Alps and Central
Massif
Bora Cold Along the Adriatic Coast
Tramontane Cold
Gregale Cold
Vegetation
Xerophytic Trees with small broad leaves, evenly spaced and never very
tall, Absence of shade, Plants face adverse conditions like heat, dry air,
drought)
Evergreen Only in regions with favourable climate Oak in Mediterranean
coasts, Eucalyptus in Australia, Redwood in California
Evergreen Coniferous Pine, Firs, Cedar, Cypress evergreen, needle
shaped leaves
Bushes and shrubs most dominant Mediterranean climate vegetation
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Conditions not favourable for grass as the rain comes in winter when growth
is slow
Economy
Orchard Farming on large scale fruit trees have long roots to draw water
from great depths, thick leathery skin of citrus fruits prevents transpiration
Olive, Chestnut, Walnut, Hazelnut
Wheat and Barley
Not suitable for livestock rearing, but mountain pastures support a few
animals
Transhumance is prevalent
Viticulture Mediterranean coast countries account for 3/4 wine production
Long, sunny summer is favourable for grapes cultivation
Tourist hotspot
Net exporter of wine and citrus fruits, net importer of dairy
Climate
Warm, moist summer and cool, dry winter (Natal climate is moist in winters
as well)
Rain throughout the year
Large annual temperature range
Strongly modified by maritime influence
Penetration of cold air from polar vortex may bring down temperatures
Rainfall is enough for agricultural purposes
Uniform distribution of rainfall throughout the year
China is under influence of onshore NE trade winds (from pacific),
southern/SE regions of S America, Africa and Australia under SE trade
winds (In summer in S hemisphere, the ST LP shifts towards S Pole)
Local storms like typhoons and hurricanes occur
Throughout the year rainfall, since the area is under unstable airmasses
3045°N/S on east Frontal precipitation in Winter
coast
China Type East coast of China, Vegetation
C southern parts of
Due to adequate rainfall, luxuriant vegetation
Japan, SE USA, NSW
Lowlands Evergreen broadleaved forests and and deciduous forest
Australia, Natal (SA),
(hardwood)
Uruguay
Highlands Pines and Cypresses (softwood)
Perennial plant growth is not checked by dry season
Quebracho (hardwood used for tanning) in South American China type
regions
Eucalyptus in Eastern Australia (also in mediterranean)
Economy
1/3 of world’s rice in China both on lowlands and highlands
SE USA corn mostly for the meat industry, cotton (Mississippi flood plains
and Atlantic coastlands), market gardening, Tobacco (humid atmosphere,
warmth, well drained soils 50% of international trade)
Southern Hemisphere Cane sugar, Cotton, Tobacco, Maize, livestock,
dairy in Australia, lumbering in Canada
Vegetation
Deciduous forest trees shed their leaves in cold season adaptation to
protect against cold and snow
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Oak, Elm, Ash, Birch, Beech, Poplar
Willows grow in wetter areas
Higher latitudes conifers which can survive lower temperature and poorer
soils
Economy
Deciduous hardwood Lumbering species are in pure stands, less
undergrowth profitable
Highly industrialised with high standard of living Ruhr, Yorkshire,
Manchester, Liverpool
Fishing in Britain, Norway and British Columbia
Dairy Denmark, Netherlands, NZ scientific basis
Milk converted to cream is exported to all regions of the world
Merino wool Tasmania
Market gardening/Truck Farming in North Western European countries
Tasmania is called 'garden state' as horticultural produce from Tasmania is
shipped across the Bass Strait to Australian mainland
Beef in Australia and Argentina
Sheep rearing in NZ (Canterbury Plains) extensive meadows, mild
temperate climate, refrigeration, scientific process
2/3 of world potato production Germany, Poland, France, UK
Beet sugar in Europe and parts of USA
D Cold Snow Forest Climate
Taiga Climate Only in N hemisphere Temperate Coniferous Forests account for highest percentage of Forest Area
due to large EW extent Merges into Arctic Tundra on the North and Steppes on the south
Absent in Southern Hemisphere narrowness of the continents, maritime
Central Canada, influence reduces the severity of winters
Scandinavian Europe, But coniferous forests are found on the uplands in Chile, NZ and Tasmania
central and southern
Russia Climate
Brief and warm summer, long and brutally cold winters
Annual temperature range is greatest in Siberia (North America extremes
are narrower due to lesser EW extent)
Local Polar Winds blizzards of Canada, Buran of Eurasia
Permafrosts are absent as ice is a poor conductor of heat and protects the
ground from severe cold above
Maritime influence in interiors is absent
Rainfall throughout the year with SUMMER maxima rainfall due to Front
Vegetation
Evergreen Coniferous Forest Taiga in Siberia, is the greatest single band
of coniferous forest
Leaves are small, thick, leathery and needle shaped to prevent loss of
moisture through transpiration
Fir, Spruce, Juniper, Birch (deciduous)
Sweden and Finland have similar types of forest
Coniferous Forest extends from Alaska into Labrador
Soils of coniferous forests are poor excessively leached and acidic
Humus content in soil is low as leaf litter is low and rate of decomposition is
low
Undergrowth is negligible due to poor soil, absence of direct sunlight and
short summer
Economy
Lumbering is the most important activity
Coniferous forest belts in Eurasia and N America sources of softwood
used in furniture, paper and pulp and rayon
USA is the leader in wood pulp production
Canada > 50% of newsprint
Hunting of furbearing species like mink, silver fox, ermine
Why is lumbering well developed in Taiga climate?
Trees occur in pure stands
Snow covered ground makes hauling easier
Softwoods float on rivers easy transport
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The Taiga forests are not too dense limited in species (Pine, Spruce and
Fir)
Cheap hydroelectricity for driving the saw mills
Absent in Southern Hemisphere as only a small section of continents extend
beyond 40°S
In Chile, Westerlies cannot reach the continent due to Andes
Climate
Between British type and Taiga
Warm wet summers, cold and dry winters
Rainfall throughout the year // Dry westerlies in winter
North America round the year precipitation
Westerlies carry depressions over Great Lakes towards eastern regions
Gulf Stream + Labrador current near Newfoundland —> Mist and Fog
Gulf Stream increases moisture in Polar Easterlies
Asia winters are drier (rainfall resembles monsoon type)
China Due to LP over Tibet, moist winds from Pacific Ocean and Sea of
Japan flow in as SE monsoon
Japan meeting of Kuroshio and Oyashio produce fog, Kuroshio makes
climate of Japan in winters less extreme
Vegetation
Heavy rains, warm summers and damp air from fogs favour growth of trees
North of 50°N, forests are coniferous (continuation with taiga)
Eastern Canada, NE Maple forests in Canada
Laurentian Climate USA and
Newfoundland
Cool Temperate Economy
Eastern Marine Siberia, Manchuria,
north Japan Exports of timber and fish
Both temperate hardwood and temperate softwood
St. Lawrence river helps in transport of timber for the lumbering industry
Agriculture in Manchuria, Korea and Japan
Apples in Annapolis region of Nova Scotia
Grand Banks off Newfoundland fishing
Gently sloping continental shelf
Mixing of cold and warm water creates upwelling of nutrient rich water
Freshwater fishing in St. Lawrence and Great Lakes
Whaling and pearl culture (mostly by Japan)
Why is fishing the main activity in Japan?
80% of land in Japan is nonagricultural, 50% of total land is covered by
forests
Not wellendowed with natural resources
No pastures for livestock farming
Technological advance in fishing gives Japan an edge
Favourable govt policies and availability of skilled workforce
Continental shelves around Japan are rich in plankton
Indented coastline provides sheltered fishing ports
Mixing of Oyasho and Kuroshio currents
E Cold Climates
Tundra Climate North of Arctic Circle Climate
South of Antarctic Circle
Very low mean annual temperature
Not more than 4 months have temperatures above freezing
Permafrost inaccessible to plants (subsoil is frozen)
Precipitation as snow or sleet convection is absent
Vegetation
No trees
Mosses and Lichens in favourable regions like the coasts
Coastal lowlands support hardy grasses and moss pasture for reindeers
Brief summer Berry bearing bushes and Arctic flowers
Penguins in Antarctica, migratory birds, Polar bears in Arctic
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Economy
Sweden Iron ore at Kiruna and Gallivare
New sea routes through Arctic icebreakers make them navigable
Gold in Alaska, Petroleum in Kenai peninsula, Copper in Canada
Tribes
Eskimos Northern Alaska and Canada
Aleuts Aleutian Islands
Samoyed Russia
Lapse Norway pastoralists (rest are huntergatherers)
Chukchi Russia
Burayat Russia (near lake Baikal)
Even in summer, temperature is below freezing point
Interior Greenland and
Ice Cap Snow and ice get accumulated and mounting pressure causes deformation of
Antarctica
ice sheets
H Highland Climate
Governed by topography
Large changes in mean temperature, humidity, precipitation types and intensity over short distances
Vertical donation of climate types with elevation
Evidences of Climate Change
Geological records showing glacial and inter glacial periods
Geomorphological features in high altitudes and latitudes having signatures of advance and retreat of glaciers
Rings in trees provide clues about wet and dry periods
Sediment deposits in glacial lakes
Sun Spots
Dark and cooler patches on the Sun which modify the solar output
More Sun spots less solar output cooler and wetter climate, storms
Millankovitch Oscillations
Cycles of earth’s eccentricity, tilt and precession and modify global climate
Precession
Determines 'how elliptical' the earth’s orbit around the sun is Eccentricity is a measure of deviation from a circle
Changes in eccentricity are due to gravitational interactions with nearby planets particularly large ones like Jupiter and Saturn
Axial Tilt
Tilt of earth with respect to a perpendicular line to orbital plane cycles between 22.1 to 24.5°
Greater tilt = hemispheres closer to Sun = Regions in extreme points of both hemispheres will have extreme summers and
winters
Precession
Wobbling of the axis due to tidal forces of moon and sun
Effectiveness of GHG molecule will depend on
Magnitude of increase in its concentration
Lifetime in atmosphere
Wavelength of radiation that it absorbs
Causes of Climate Change
Sunspots
Millakovitch Cycles
Volcanos throw up aerosols which reduce the sun’s radiation
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