Climatology

Origin of the atmosphere on the earth

Structure of atmosphereHeat BudgetAlbedoMovement of airStability and instabilityAdiabatic lapse rateTemperature Inversion

Precipitation processes: evaporation- Humidity - condensation-clouds

Types of cloudsTypes of rainfallPressure system of the worldPlanetary wind systemVariable winds

Temperature decreases with increasing height

GHG gas absorb long wave terrestrial radiation – transparent to insolation (short wave radiation)

Heated from terrestrial radiation from earth surface

Troposphere

Structure of Atmosphere

Temperature increases with increasing height

Ozone layer absorbs UV rays from Insolation

Stratosphere

Structure of Atmosphere

Temperature decreases with increasing height

Absence of GHG gasGoing away from Ozone layer

Mesosphere

Structure of Atmosphere

Temperature increases with increasing height

Gases are in ionic state –extremely hot

Ionosphere -Imp for radio communication

Thermosphere

Structure of Atmosphere

Movement of air Adiabatic lapse rate

Basic air movement

Temperature Inversion

Ex. Of Temp Inversion - tropopause

Temperature Inversion

Ex. Cool winter night

Ex. Valley inversion

Temperature Inversion

Evaporation

Relative HumidityAddition of moisture or reduction of moisture holding capacity of the air packet = rainfall

1) Addition through evaporation

2) Reduction through upliftment of the air

Humidity

Precipitation process

Condensation- clouds

Types of clouds according to their height and shape

Nimbus clouds give rainfall

Cumulonimbus cloud – indication of instability

Cyclonic heavy rainfall

Precipitation process

Convectional rainfall Orographic rainfall

Types of rainfall

Cyclonic rainfall Frontal rainfall

Types of rainfall

Pressure system of the world

High pressure to low pressure

Coriolis force – clockwise in northern hemi and anti-clockwise in southern hemi

Trade windsWesterliesPolar easterlies

Planetary wind system

•Around tropopause, there is only one gradient•Wind accumulated above equator and rarified atmosphere above poles•HP at the equator and LP at the poles

Upper tropospheric winds

LP

HP

LP

HP

•strong coriolis force at tropopause•Because friction is less - high speed - stronger the coriolis force•So the deflection is 90 degree•Such winds called geo-strophic winds

Geo-strophic winds

Equator

Poles

•Northern hemisphere

Geostrophic deflect clockwisewest to eastIn southern Hemisphere: Anti-clockwise movementDeflect west to east

Geo-strophic winds

Poles

Poles

Equator HP

LP

LP

Westerlies winds

•The upper tropospheric winds / geo-strophic winds blow from west to east at the very high speed

•Westerlies at poles – to maintain the angular momentum- they meander => Rossby waves•Rossby waves do not meander consistently, but follow a cycle = Index cycle

Rossby waves

• In westerlies, there are strong, narrow bands of high speed wind => Jet stream•Speed of Jet stream 300kmph

Jet streams

•There are situated at the margins of meridional cells•4 permanent Jet streams: 2 Polar Jet and 2 Sub-Tropical Westerly Jet STWJ

Jet streams location

STHP Eq. LPSPLPPolar High

Permanent jet stream

Temporary jet stream-TEJ

Jet streams

Tibet plt. LP

Mascerene High

Tropical Easterly Jet

SW Monsoon winds

Somali jet stream/ Findlater Polar-night Jet

Temporary Jet Streams

summerwinter

Polar night Jet stream

Somali Jet stream

• Jet stream embedded in westerlies (Rossby waves) at high latitude, cause pressure variability•That’s why they are called travelling depression

Jet streams

Jet Stream – travelling depressions

Weather of higher latitude is more complex than weather of equatorial or tropical regions

Because tropical and equatorial region are heat surplus region– thermal reasons play the dominant role.

But higher latitude are heat deficit region – dynamic reasons play dominant role

These include – localised + upper-tropospheric circulations (Rossby waves, Jet streams, temperate cyclones)

Weather of Mid and high latitude

Thermally induced

Because of high temperature

Ex. LP at equatorConvectional rainfall at equator

Upliftment of warm air

Ex. LP at sub-polar LP belt

Frontal rainfall

Dynamically induced

Conditions for LP

• Large extensive body of air-mass (1000sqkm)•Height upto Tropopause•At particular height, one air mass will have uniform temperature and moisture across its width•Airmasses can be differentiate according to their temperature and moisture content

Air mass

•Air mass acquired properties from the source regions – land, marine, polar, arctic, Antarctic = give them identity. Ex. mP, cT•Extensive homogeneous surface + longer stay (HP)

Air mass

•Air masses do not stay at their source regions forever, they move out. While moving they came across other air masses.

Air masses

•The relative difference between temperature and moisture decide their interaction with one another•The border/ meeting region of the two air-mass => Front

Front

Cold front

Warm front

• If cold air mass move faster than the other than it will lift the warmer one upward => cold front• the slope will be steep = there will be sudden up-liftment of the warm air = cumulonimbus clouds = cyclonic rain

Cold front

Cold air mass

• If warmer air mass is more active than cold front => warm front •slope will be gentler = there won’t be sudden up-liftment of warm air = uniform prolonged rain – drizzle

Warm front

Fronts

Cold front Warm frontCold front

Warm front

Cold air mass

warm air mass

Cool air mass

•Also called as extra-tropical cyclone, travelling depressions, cold-core cyclone, wave cyclones

Frontal cyclone

1) Intense LP system2)Air converges

towards the centre3)In Northern

hemisphere convergence – anti-clockwise

4)Closed isobars

Meaning of cyclone

Normal isobar Closed isobar

Isobar

Thermally induced

Because of high temperature

Ex. LP at equatorConvectional rainfall at equator

Upliftment of warm air

Ex. LP at sub-polar LP belt

Frontal rainfall

Dynamically induced

Conditions for LP

•Movement of airmasses from their source region•The warm and cold air mass face each other•A front is created between them •Called Stationary front

Development of Frontal cyclone

Location of air masses Circular movement

Formative stage of frontal cyclone

•Cold air mass pushed the warm air mass•Forced upliftment of warm air mass at the cold front =LP •Two cold air mass convergence – circular due to coriolis force

Development of Frontal cyclone

Interaction of air masses LP – closed isobars

Mature stage

• One cold air mass climb over other cold air mass–warm front is destroyed•Called occluded front•Rapid change in temperature and pressure•Unstable weather conditions

Occluded front

•Frontolysis – no great temperature difference between two cold air masses – front dissipated – LP reduced – cyclone dissipated

Dissipation of frontal cyclone

Stationary front Front

Occluded front Frontolysis

•Always west to east direction•Because influence of the Westerlies •Gradual and predictable movement

Path of the temperate cyclone

Distribution of temperate cyclonesTemperate cyclones

Hurricane –N. AmericaTyphoon - China•Late summer • Increased sea surface temperature = LP

Tropical cyclone

•Convergence of air around LP zone•Rising moist (wet) air => absolute instability•Cloud formation =more and more moisture – latent heat of evaporation => cumulo nimbus cloud => cyclone

Tropical cyclone

• Intensification of LP•Converging air near water surface•Circulating air rises above (coriolis force)•Diverging air at the top of cyclone

Mature Tropical cyclone

•At the centre of the cyclone – ‘eye’ of the tropical cyclone.• It is a pressure defect. Because, at ‘eye’ a narrow stream of wind descend = is HP at ‘eye’•At the eye, there is clear sky.•Beyond eye wall – extreme low pressure

Eye of the tropical cyclone

•Move swiftly•Always east to west• It is fuelled by moisture – so when cyclone is cut-off from sea and move towards land – it starts weakening

Properties of tropical cyclones

Distribution of tropical cyclone

Temperate cyclone

30-40 degree latitude

Dynamically induced

Due to frontal interaction

Formed over large area

Move west to eastGradual movement – predictable

8-20 degree latitudeThermally inducedDue to increasing SST

Small areaMove east to westSwift movement- difficult to predict path

Tropical cyclone

comparison

Temperate cyclone

Wind speed 40-50 kmph

Pressure gradient 980 mb

Powerful on landAffect mainlandMore time to dissipate

Wind speed >120 kmph

Pressure gradient <880 mb

Weakens on landAffect only coastal areas

Quickly dissipate after coming on land

Tropical cyclone

comparison

Mains2014

Q. Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why? (10)

UPSC

Question

1) Tropical water2) Warm ocean

currents3) Increase SST

in late summer

4) Tropical cyclone move east to west

5) Landmass on western coast

Reason for location of Tropical cyclone

•Local storm • for short period of time•Heavy rainfall with thunder and lightning

Thunderstorm

•Strong upward movement of warm moist air•Atmospheric instability•Cumulonimbus clouds•convectional rainfall

Thunderstorm

Stages of thunderstorm

1) Air motion mostly upward2) When accumulated load of water and

ice becomes excessive –downdraft starts. Descending water droplet evaporate- cool the air – increase more downdraft action

3) Downdraft spreads throughout the cell

Stages of thunderstorm

•Within thunderstorm – updrafts, downdrafts, ice and water particles•Thunder clouds produce excessive negative charge at height where temp is btwn -5 to -15 deg c•+ve charge at higher and lower altitude

lightning

•Create high electric field•Reason unknown•When accumulated charge becomes large-•Lightning between opposite charge within cloud, to ground, to neutral atmosphere

Lightning

Types of thunderstormthunderstorm

Thermal

orographic

Cold front

•Localised intense heating of ground during summer afternoon•Equatorial regions•Die out if passes over water body because absence of supply of heat

Thermal thunderstorm

•Warm moist air when passes over mountain barrier•Forceful upliftment – latent heat of condensation• ‘Cloud burst’• In Cherrapunji during monsoon

Orographic thunderstorm

•Active air masses –forceful upliftment of warm moist air•Localised and short-lived

Cold front thunderstorm

Prelims2001

Q. Which one of the following weather conditions is indicated by a sudden fall in barometer reading?a) Stormyb) Calm weatherc) Cold and dry weatherd) Hot and sunny weather

Ans. A)

UPSC

Question

• It forms on land •Higher wind speed than tropical cyclone•But smaller than tropical cyclone• Intense LP system•Exact mechanism unknown

Tornedo

•When tornado passes over a water body –water is sucked up towards center of tornedo•Called water spout

Water spout in tornado

Distribution of tornedo in world

•Occur mostly in temperate regions (20 to 60 deg N,S)•Where cold polar air meets warm tropical air•USA, South-west of great plain – “tornado alley”

Distribution of tornedo in world

• It is a large scale cyclone that encircles geographical poles of the earth•Span =1000 sqkm

• It develops at upper troposphere or stratosphere

Polar vortex

• It originated during winters due to sharp temperature differential created between poles and equator •Development of Polar night Jet streams•Circular movement

Polar vortex

•Rossby waves can disrupt the circulation around the polar vortex•North moving warm air masses and HP systems

Polar vortex

•Disruption in polar vortex can push part of its frigid air pockets to southward •Produce ‘ cold waves’• Jan 2014 in USA

Cold wave – polar vortex

Polar vortex in USA 2014

•Nacreous cloud/mother of pearl•Polar stratospheric clouds formed in winter during polar vortex.• temperature below -80 degree – 12 -22 km height•Contains water, Nitric acid and sulphuric acid

Polar stratospheric clouds

•Nitric acid in polar stratospheric clouds reacts with CFC -create chlorine•Chlorine concentration in winter• in summer -Chlorine reacts with oxygen molecule of ozone - destruct the ozone molecule

Ozone depletion

• Increased level of CFC in atmosphere•Winter - Polar vortex more concentration of chlorine •Summer – more destruction of Ozone layer

Ozone depletion

•Polar vortex in northern hemi are weak and not as cold as formed at Antarctica•Ozone depletion at Arctic = ‘Ozone dent’•ozone depletion more at southern pole = ‘Ozone hole’

Ozone depletion

Montreal Protocol, 1987 (1989)

Restriction over usage and release of CFC gases and HFCs

197 countries ratifiedMost successful international environmental treaty

In 2014 recovery of ozone layer found

Protocol

Ozone hole

Vertical: Hadley, Ferrell Horizontal: walker

Pressure gradient cells

Ferrel cell

•There are oscillation in pressure gradient and air circulation after intervals of 2-3 years in south Pacific Ocean•Called Southern Oscillation•ENSO = EL Nino Southern Oscillation

Walkar cell at south Pacific

•South equatorial current pile up water at northern Australia – increase SST – called West Pacific Pool• It brings rainfall in Northern Australia

Normal year

West Pacific pool LP HP

•The diverging air above Australia move towards Peruvian coast•They descend at Peruvian coast = HP – desiccating effect to Atacama desert•Completes the Walker cell

Normal year

LP HP

•As south equatorial current take water from east to west, it led water from bottom to come up and take the space•Up-welling at the Peruvian coast = rich fishing ground

Normal year

HPLP

Down-welling

•Direction of walker cell reverses•South equatorial current weakens (reason unknown)•Weak piling up of water at Northern Australia•Weakening of west Pacific Pool

El-Nino year

LP HP

•Ocean water move towards Peruvian coast. Create LP system over there and rainfall at Atacama desert•The rising and diverging wind above Peru descends over Australia = HP condition – drought in Northern Australia

El-Nino year

LPHPAustralia Peru

•The reversal in wind direction alters submarine cycle as well•Down-welling at Peruvian coast => loss in fishing business

El-Nino year

Down-welling

Down-welling

Upwelling

Upwelling

•El-Nino bring drought condition in Indonesia as well – forest fire• It is responsible for weak monsoon in India

Implications of El-Nino

•Association of El- Nino or Western Pacific Pool with Indian Monsoon •There can be other atmospheric cells associated with Western Pacific pool•Still undiscovered

Implications of El-Nino on Indian Monsoon

Mascarene HighWestern pacific Pool

HP

LP

LP

With global warming there will be increasing number of El-Nino events

It is a global phenomenon. Though happening in limited area, it may have wider implication over the globe

Global Implications of El-Nino

• Intensification of walker cell• Strong west pacific pool•Heavy rainfall – flood condition in Northern Australia – good monsoon in India•Drought in Atacama•Very good fishing business at Peruvian coast – price crash

La-Nina

ThunderstormTornadoEL-Nino La-Ninaimplications

Climatic regions of the world

1) Equatorial region2) Tropical monsoon3) Savannah4) Steppe5) Hot desert6) Continental

deserts

7) Mediterranean climate8) China type9) British type10) Laurentian type11) Taiga12) Tundra 

Climatic regions of the world

Equatorial regions in the world

•5-10 degree latitude•Same season (weather) throughout the year•Direct sunlight – heat surplus – LP condition every day – rising of moist air – advection rain every evening•Hot-wet climate

Equatorial climate

•Dense forest –rainforest –lungs of the earth•High biodiversity• Tall trees (Abony, Rosewood, mahogany, rubber) – epiphytes •But not good for lumbering – hardwood – high diversity – loading-unloading very difficult

Equatorial climate

•Amazon rainforest is being cleared for rubber plantation, oil exploration • Yasuni national park in Ecuador– cleared for oil extraction – biodiversity is more than entire north America - 2 un-contacted tribes •Rainforest of Indonesia- cleared for oil-palm cultivation

Equatorial climate

•Equatorial climate•not good for habitation hot and moist climate•High incidents of malaria and diseases

Country Primitive tribe

Congo Pigmy

Malaysia Semang, Orang Asli

Philippines Orang Akita

Borneo Dayaks

Equatorial climate

Prelims2013

Q. Which of the following is/are characteristics of equatorial forests?1. Presence of tall, closely set

trees with crowns forming continuous canopy

2. Co-existence of a large number of species

3. Presence of numerous variety of epiphytes

UPSC

Question

Prelims2013

a) 1 onlyb) 2 an 3c) 1 and 3d) 1,2 and 3

Ans.d)

UPSC

Question

•Sub-tropical HP belt•Off-shore trade winds – by the time rain bearing wind reach from east to west – they become dry –so no rain on western coast in Northern hemisphere and southern hemisphere

Tropical desert

STHP

STHP

STHP

STHP

•desiccating effect of cold oceanic current on western coast of continents

Tropical desert

•Arid-dry climate, scanty rainfall, water deficit •Vegetation – Xerophytic • Low population – Maghreb region – high poverty• Tauregs of Sahara, Beduins of Arabia Hottentots of Kalahari desert

Tropical desert

• Interior of large land•Rainfall bearing winds cannot reach there•Leeward side of the mountain•Aridity (but no sand dunes)•High annual temp range

Continental desert

China South America

Continental deserts

TIEN SHAN

ALTUN SHAN

ANDES Range

•Negev Desert•Kalahari Desert•Namib Desert•Atacama Desert•Takla Makan•Rub –al-Khali

•Dast-e-kavir• Dast-e-lut•Nubian Desert•Patagonian Desert•Great Sandy Desert•Simpson Desert• Great Victorian Desert

Deserts to locate

• It is also called savannah, the “park land topography” or “big game country”•Located between rain forest and hot desert

Tropical grassland

Llanos, Campos – S.Ame Savannah -Africa

Tropical Grasslands

Campos

c

•Moderate rainfall – clear dry-wet season•Tall grass ‘elephant grass’, scanty large trees, grass-fire in dry season – way of controlling trees•Large carnivorous animals

Tropical grassland

•Acacia tress with broad trunks – baoab trees and bottle trees•To store water•Grass – long roots, remain dormant in dry period•Australia – Mallee, Mulga, Spinifex grasses

Tropical grassland

•Tribes = Masai tribe (kenya) – Pastoralist •Hausa and Aibo tribes of Nigeria

Tropical Grasslands

Prelims2012

Q. Which one of the following characteristics of climate of Tropical Savannah region?a) Rainfall throughout the yearb) Rainfall in winter onlyc) An extremely short dry

seasond) A definite dry and wet

season

Ans. D)

UPSC

Question

Continents Names North America

Prairies

South America

Pampas

Central Asia SteppeSouth Africa

Veldt

Australia Downs

Temperate grasslands

•Cooler and wetter than Savannah •Under westerlies•Perfect grassland – no trees •Grass is very nutritious

Temperate grasslands

•Temperate grasslands entirely converted into agriculture. •Prairies: Truck-farming – large acres of farmlands – extensive use of machinery- •High productivity per person

Truck-farming

•Wheat, cotton and Maize cultivation•USA:•Prairies: maize is fed to animals – fattening – slaughter house near great lake region

Prairies, North America

•Pustaz in hungary

•Wheat bowl of the world

• ‘Black Earth’

•Sugar from sugar beet

Steppe, Asia

•Livestock ranching•Alfalfa nutrious grass•Argentina –wheat exports•Buenos Aires and Montevideo - •Meat and dairy exports

Pampas, South America

•Australia: sheep rearing, meat

•New Zealand:

•Canterbury plains

•Sheep rearing

Downs, Australia

DOWNS

•Veldt (Dutch word) = field•Basins of Orange river and river Limpopo – sheep rearing, agora goat•Wool production

Veldt, Africa

Orange river

Limpopo river

• India, Thailand, Cambodia, Myanmar, Laos, Vietnam, Northern tip off Australia•Eastern Brazil •Gulf of Guinea coast and around horn of Africa in Africa

Tropical Monsoon

•On shore trade wind seasonal reversal of winds•During summer, sun move northward •With sun, LP ITCZ also move •Thus, entire wind system shift northward

Tropical Monsoon

• The region which was under northern trade winds, come under southern trade winds•Northern trade winds blow north to south, while southern trade winds blow south to north• it seems reversal of winds in the region

Tropical Monsoon

ITCZ

ITCZ

•Distinct wet and dry season – rainfall in confined to 4 months – vulnerable to drought and flood•Similar to savannah but wetter than savannah

Tropical Monsoon

•Tropical deciduous forest – distinct autumn season – shedding of trees •Trees: Indian subcontinent – Sal, Teak (Myanmar Teak)•Hardwood

Tropical Monsoon

• Intensive agriculture, subsistence farming•High population density, small land holding•High productivity per acre – per person low•Crops: rice, sugarcane, jute, cotton, indigo, spices

Tropical Monsoon

• Shifting cultivation/ slash and burn cultivation/ Jhum cultivation• forests are cut, burnt and cultivated.•When soil fertility began to decline, the land is abandoned, and a new patch of forest is burnt. •By the time abandoned land regenerated for several years until the next round of cultivation.

Tropical Monsoon

against

Deforestation higher run-off of rain water in hilly areas -Water scarcity during non-rainy days

loss of biodiversity

Jhum uses natural cycle of forest regeneration (6-10 years)

Cause temporary loss of forest patches

No use chemical fertilizers or pesticides + diversified crops

favour

Jhum cultivation

the dry the cut trees are dried under the sun- burn the trees – ashes of the burnt trees (Potash) replenish the soil nutrients

The regenerating forest provides forest produce to the people

Settled agriculture- monoculture plantation of pineapple, rubber and oil palm – cause permanent loss of forest

Once monoculture adopted with chemical inputs, the same land cannot be converted into natural forest

Jhum cultivation

Country Term for shifting cultivation

Malaysia LadangMyanmar TaungyaThailand TamraiPhilippines CainginJava HumahShri Lanka ChenaAfrica Milpa

Different names of shifting cultivation