geo l5 oceanography_part2_0.2

OceanographyClimatology

Topics under Oceanography

Ocean Bottom Relief

Ocean Currents

Ocean Tide

coral reef

Temperature of Oceans

Salinity of Oceans

Ocean bottom relief

petroleum Sulphur

Resources from continental shelf

Placer deposit Pearls, fish, calcium

Resources from continental shelf

Continental slope Continental rise

Continental margins

Poly-metallic nodules Indian exploration

Abyssal plain

Continental Islands Volcanic islands

Types of Islands

Sand-bar islands Coral Islands

Types of Islands

formation

Symbiotic relationship between coral polyps and xooxanthalae

Sunlight –depth 50 m

Temp – 25-27 degSalinity – 33Calm, circulating nutrient rich water

Not at mouth of river

conditions

Coral reef

Coral bleaching

Coral polyps expel xooxanthalae under stress condition

Global warmingOzone depletionOcean acidificationSedimentationMarine pollutiondiseases

Reasons for bleaching

Coral reef

•Fringing reef – barrier reef- atoll•Subsidence theory of Darwin•Standstill theory of Murray

Formation of coral reef

Horizontal •waves•currents

Vertical •tides•Up-welling

Motion of Ocean water

waves Ocean currents

Horizontal motion of ocean water

tides Spring-neap tide

Tides

Upwelling Down-welling

Up-welling and down-welling

Temperature of the ocean

Salinity of the ocean

Main energy source - InsolationOceans play important role in energy and temperature regulation on earth, due to specific heat of the water

Average temperature of ocean = 3-5 degree Celsius

But average surface temperature of ocean water = 25 degree

Temperature of Ocean

•Latitudinal variation• It decreases from equator to poles•But highest temperature is not at the equator but at the tropics•Reason: high rainfall, cloud cover (high albedo/ reflection of sunrays)

Temperature Pattern of the Ocean

•Hemispheric variation•Northern hemisphere warmer than southern•Reason: large land mass in northern hemisphere – high energy

Temperature pattern of the Oceans

•Enclosed seas•Marginal seas of tropics warmer than open Ocean + marginal seas of temperate region cooler than open seas•Reason: less mixing of water

Temperature pattern of the Oceans

•Ocean currents•Warm ocean current –warming effect•Cold ocean current cooling effect

Temperature pattern of the Oceans

•Up-welling and dow-welling•Upwelling bring cool water from depth –lower down the surface temp

Temperature pattern of the Oceans

•Down-welling – piling up of warm water – increase the temp

Temperature pattern of the Oceans

•Max temp of day and min temp of night time•Tropical water higher diurnal range than equatorial waters•Because, Heating and cooling of water rapid under clear sky

Diurnal range of temperature

•Bigger the size of ocean- better mixing of water and heat•Lower annual range•Pacific ocean –lower annual range than Atlantic Ocean

Annual range of temperature

Prelims

2007

Q. Consider the following statements:1) Annual range of temperature

is greater in Pacific ocean than in Atlantic ocean

2) Annual range of temperature is greater in northern hemisphere that in southern hemisphere

UPSC

Question

Prelims

2007

Which of the statement is correct?a) 1 onlyb) 2 onlyc) Both 1 and 2d) Neither 1 or 2

Ans. B) Pacific Ocean – better mixing

UPSC

Question

1st layer – upto 500m(20-25 deg C)2nd layer – thermocline 500-1000m 3th layer – cold layer –beyond 1000m

Vertical distribution of temperature

•Temp decreases with increasing depth• rate of decrement is rapid at equator –tropics than towards poles•1st layer – permanent in Tropics– temperate only in summer

Vertical distribution of temperature

Temperature of the ocean

Salinity of the ocean

Amount of salt found in 1000 gm of water

Nacl (78%), MgCl2 (11%), MgSO4 (3.5%), CaSO4 (2.5%)

Na and Cl has high residual time in ocean water – very gradual removal – that’s why, they remain in the highest proportion

Salinity of Ocean water

Irrespective of absolute salinity of the water, the proportion of the salt remain same in all parts of the oceans

Amount of addition or extraction of fresh water compared to salt content in the Ocean water decides absolute salinity of the Oceans.

Salt Budget

Sediments carried by riversSubmarine volcanism at MORChemical reaction between rocks of geothermal vent of volcano and cold water

Erosion of oceanic rocks

Sources of salts in ocean water

Physical removal – waves break at the beaches, salt-spray

Biological removal – marine life forms extract calcium from sea water for their bones

Removal of Salts in Ocean water

Addition of fresh water => Rainfall, inflow of large river, melting of glacier => less salinity

Reduction of fresh water => increase in temperature, high evaporation, windy (wind accelerate the evaporation)

Variation in salinity

Standard salinity of ocean water is = 35.5 ppt – salinity of Atlantic Ocean

Dead Sea (350 salinity), Lake van (400), Lake Urmia

Man seldom drowned in sea with high salinity

Because, high salinity = high density

Salinity of the oceans

•Salinity goes decrease from equator to poles•But highest salinity is not at the equator = because high rainfall, cloud cover•Highest salinity is at tropics

Pattern in variation of salinity

•Northern hemisphere – warmer – high evaporation – saline•But in southern Pacific- roaring 40, furious 50 and shrinking 60 screaming 70 – very fast winds •High evaporation => high salinity

Pattern in variation of salinity

•1st - Ocean currents•warm ocean current like, high evaporation•Cold current led to Up-welling: cooler water from depth come at the surface => low salinity

Local Variations in Salinity

•2nd - Enclosed seas • low latitude - warmer than open sea- high salinity•Ex. Mediterranean Sea, Red sea •high latitude- cooler than open sea – low salinity•Ex. Baltic Sea

Local Variations in Salinity

•3th – inflow of large rivers• Ganga – Brahmaputra flow into Bay of Bengal•Bay of Bengal less saline than Arabian sea

Local Variations in Salinity

Mississippi in G.of Mexico

Amu darya, Syr darya to Aral sea

Rivers inflow to the seas

Black sea Persian gulf

Rivers inflow to the seas

•4th – glaciers•Baltic sea receive fresh water from melting of glaciers – low salinity

Local Variations in Salinity

Salinity decreases with increasing depth

Temp of water decreases Density of water increasesSalinity increases density –water sinksSaline water freeze slowly compared to pure water

Vertical pattern of salinity

Equator – salinity increases with depth upto some layer –than decreases with depth

Beyond equator – salinity decreases with depth

Vertical salinity variation of oceans is complicated

No uniform layering

Vertical pattern of salinity

Temperature of ocean watervariationsSalinity of ocean waterSalt budgetvariations

Climatology

•Early atmosphere has H and He in abundance -lighter gases escaped•During early life of the earth – extensive volcanism- degassing. N, S, Water Vapour, Argon and CO2 came out

Origin of the Atmosphere on Earth

•Water vapour condensed – clouds – rainfall –washed out bulk of the CO2 into Oceans. Co2 = 0.03%•Oxygen – from anaerobic respiration of bacteria like, Cynobacteria

Origin of the Atmosphere on Earth

Gas ProportionNitrogen 78%Oxygen 21%Argon 0.93%Carbon dioxide 0.03%Neon 0.0018%Helium 0.00005%ozone 0.00006%

Proportion of gases

N, O, H and Argon are permanent gases

Water vapour, Co2, ozone -> variable gases, GHG

N, Argon – inert gases Atmospheric gases- no chemical interaction among them

They don’t lose their propertiesThey act as a single unified gas

Proportion of gases

Structure of atmosphere

•90% of atmosphere within 32 km•Tropopause = Height 8 km at poles, 18 km at equator•At equator cumulonimbus clouds

Troposphere

•Temperature decrease as height increases•Transparent to insolation (shortwave)•Heated by terrestrial radiation (longwave)•GHGs absorbs long wave terrestrial radiation

Greenhouse effect in troposphere

Prelims2012

Q. normally, the temperature decreases with increase in height from the earth’s surface, because,1. Atmosphere can be heated

upward only from earth’s surface

2. There is more moisture in upper atmosphere

3. The air is less dense in upper atmosphere

UPSC

Question

Prelims2012

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

Ans. C)Less dense = less amount of GHGs = low temp

UPSC

Question

•Temperature increases with height•Because of the presence of ozone layer•Ozone absorbs UV rays from isolation

stratosphere

Prelims2011

Q. The jet aircrafts fly very easily and smoothly in lower stratosphere. Why?1. There are no clouds or water

vapour in lower stratosphere2. There are no vertical winds in

lower stratosphere

Ans. 1 in wrong, 2 is correct

UPSC

Question

•Absence of GHGs•Temperature decreases with height

Mesosphere

Mesospheric clouds•Clouds visible at high latitudes•During summer season •Condensation of mixture of meteoric dust and some moisture

Noctilucent clouds

•Temperature increase with height•Gases in ionic state – trap insolation – extremely hot•But ions are highly dispersed•Up to 800 km from earth

Thermosphere

•From 80km to 640 km•Number of ionic layers•Useful in radio-communication

Ionosphere

•High energy sunrays and cosmic rays break the atoms of air molecules – become ionised (+ve charged)•Behave as free particles•At night time, only cosmic rays ionization -weak

Ionosphere

layers height Frequency Presence formation

D 60-90km LF Day-time Solar radiation

E 99-130km MF, HF Day-time UV with N molecule

F 150-380km

MF, HF Day &night

G >400km MF, HF Day & night

Layers of Ionosphere

Prelims2011

Q. A layer in Earth’s atmosphere called ionosphere facilitates radio communication. Why?1. Presence of ozone cause

reflection of radio waves to earth

2. Radio waves has long wavelength

Both statements are wrong

UPSC

Question

•Beyond 640 km•Highly rarified atmosphere•Very high temperature- but different from air temperature- because no existence of air- temp can’t be felt

Exosphere

•Glowing lights at mid-nights at high latitudes•At height of exosphere and magnetosphere

Aurora

•sun emit solar wind/storm from its corona•Solar wind consist of plasma (free electrons and +ve ions)• Interaction of solar wind with earth’s magnetosphere -disturbance

Aurora

•Collision of charged particles (isonization) in magnetosphere• Ionised particles emit light –release energy•charged particles interact with geomagnetic field lines•Thus, visible on high latitudes

Auroras

•The average temperature of the earth 15 degree•Earth maintains influx and out-flux of the energy, but out-flux is not immediate, it has long time gap. That is why, the temperature is maintained.

Heat budget

•First 35% absorbed by Ozone layer•Then 15% by cloud cover•Only 50% energy reached to the earth surface

Heat budget - Incoming

•20% is lost in latent heat of evaporation 10% lost in sensible heat (temperature of the body) •15% absorbed by GHGs•Remaining 5% was released in the space

Heat budget - outgoing

•Ratio between the total solar radiation falling upon a surface and the amount reflected•Represents as %•Earth’s avg. Albedo = 35%•Lowest- dark soil• highest - snowfall

Albedo

surface AlbedoFresh snow 80%-90%Desert 35-45%Grasses 26%Crops 15%Brick - concrete 10-20%

Albedo - table

Prelims2010

Q. Which one of the following reflect back more sunlight as compared to other three?a) sandy desertb) Paddy cropsc) Land covered with fresh snowd) Prairie land

Ans. C)

UPSC

Question

Horizontal

when there is pressure gradient

from high pressure to low pressure => advection

when air get warm, gets expands, becomes lighter => move upwards => convection

vertical

Movement of air

•When air gets hotter than surrounding air, it rises upward• If it has moisture - latent heat of condensation – more heated – will go up - form clouds -can bring rainfall = instability

Vertical movement of air - instability

•When air is cooler than surrounding –it cannot move upward• sinking air• atmospheric stability or anti-cyclonic condition•High pressure on ground

Vertical movement of air - stability

Low pressure – High pressure

•The rate at which air packet cools while rising•Avg adiabatic lapse rate is 6.4 degree/km•That is air packet gets cool by 6.4 degree after covering one km upward

Adiabatic lapse rate

• if air packet has high moisture content- not get cool so fast. • Its adiabatic lapse rate <6.4 degree/km ~ 4 degree/km => WALR•Wet air can reach higher distances with low lapse rate => create instability

Wet adiabatic lapse rate

• If air packet is dry, it does not have much moisture, it will get cool very fast. More than 6.4 degree/km – like, 10 degree/km. •Dry air create stable condition

Dry Adiabatic Lapse rate

situation conditionConditional stability when wet ALR< normal

ALR < dry ALRAbsolute stability when normal ALR< wet

ALR < Dry ALR

Absolute instability when wet ALR< Dry ALR< normal ALR

Conditions of stability and Instability

•Normally, with increasing height temperature of air decreasing, but reverse is happened than it is called temperature inversion

Temperature Inversion

•1st •At Tropopause – temperature starts increasing from here•So air packet reach till here, start moving downwards

Ex. Of temperature Inversion

•2nd •A cool winter night, the air above the cold surface gets cool. •But the air layer above that cool layer is till warmer. Then, by going upward, air does not get cooler but warmer

Ex. Of temperature Inversion

•3th•Valley inversion•winter – cool air descends to valley•Uplift the warm air of valley•Descending cool air- damage crops- frost

Ex. Of temperature Inversion

Formation of fog Warm air cooled by cold air below – condensation – tiny water droplets- low visibility

Formation of frost Water moisture frozen with contact cold surface- damage to crops

Atmospheric stability Prevents upward or downward movement of air- Discourage rainfall

Implications of temperature inversion

mains2013

Q. What do you understand by phenomenon of “temperature inversion” in meteorology? How does it affect weather and habitants of the place? (5)

UPSC

Question

Condensation of water droplet Result

At heights Clouds

At lower level Fog

on the cold surface Dew drop

Turn into ice crystal in extreme cold conditions

Frost

Condensation of water droplets

Advection Moving of warm air over coldRadiation Winter nights – loss of heat

due to terrestial radiation – cold surface. Moving of warm air over cold surface

Ocean current

Meeting of cold and warm ocean currents

Reason for formation of fog

Mist

Haze Fog Sm

og

Decreasing level of visibility

fog

Water droplet condensed around a dust particle

It reduces the visibility, damage the crops

Water droplet condensed around a particle of pollutant, like SO2

Reduce visibility + health hazard

smog

comparison

Smog

It occurs in warm, dry and sunny climate

Mixture unsaturated hydrocarbons and nitrogen oxides (NO2) in presence of sunlight

Its components are ozone, nitric oxide, acrolein, and formaldehyde and peroxyacetyl nitrate (PAN).

Photochemical smog

comparison

It occurs in cool humid climate

It is a mixture of smoke, fog and sulphur dioxide (SO2).

Prelims2013

Q. Photochemical smog is resultant of reaction amonga) NO2, O3 and peroxyacetyl nitrate

in the presence of sunlightb) CO2, O2 and peroxyacetyl nitrate

in the presence of sunlightc) CO,CO2 and NO2 at low

temperatured) High concentration of NO2, O3

and CO in the evening

UPSC

Question

Prelims2013

Photochemical smog:NO2, Ozone + sunlight

Ans. A)

UPSC

Question

Structure of atmosphereVertical Movement of airAdiabatic lapse rateTemperature inversion and its effects

fog

evaporation Humidity condensation Precipitation

precipitation

1) High temperature2) LP conditions3) Fast moving wind•Water vapour evaporate from the water body•Evaporation adds moisture in the air

Evaporation

Absolute Humidity

Weight of water vapour in unit volume of moist air

Weight of water vapour per unit weight of dry air

Specific Humidity

Humidity

•Precipitation – when air is saturated with water vapour and any extra addition result in precipitation

Relative Humidity:•Amount of water vapour present in air – to amount of water vapour required for saturation

•Precipitation depends upon temperature and moisture content of the air•Hot air – saturation reach with more moisture content than cold air

Precipitation

Types of clouds

Convectional rainfall Orographic rainfall

Types of rainfall

Cyclonic rainfall Frontal rainfall

Types of rainfall

Entire earth is divided into 4 large pressure belts

In reality, belts are not continuous but pockets of low and high pressure.

But pressure can be created through thermal or dynamic reasons

Thermal: high temperature=> LP, low temperature => HP

Dynamic: air rises => LP, air descends => HP

Pressure system of the world

•4 belts:•equatorial low pressure belt•sub-tropical high pressure belt• sub-polar low pressure belt•Polar High pressure area

Pressure system of the world

Equatorial LP belt

•Constant insolation•Air gets warm -LP•Air move upward -> cloud formation -> instability -> rain in the evening daily•Cumulonimbus clouds•Convectional rainfall

Equatorial LP belt

•Absence of advection of air•Belt of calm / Doldrum•Because light, feeble winds - calm region

•The air above equator move towards pole, but coriolis force - their path get deflected. •The length of path increases. Their energy reduced in mid-path -cooled. air subside near 30-40 deg latitude.

Sub-tropical HP belt (STHP)

•As descending air – HP•Dynamically induced HP•Called ‘horse latitude’

Sub-tropical HP belt (STHP)

•From the pole, cold winds move towards equator•The both warm and cold winds collide, the warmer winds from STHP rise above the cold polar winds•This rising of warmer wind near 50-60 degree create LP

Sub-polar LP belt (SPLP)

•Air risen at SPLP, descends at poles•High pressure conditions•Thermally induced

Polar high

winds

Permanent wind

Planetary winds

Variable wind

Seasonal winds

Local winds

Mt.-valley breeze

Land-sea breeze

Wind system of the world

•winds blowing at the same direction throughout the year•cover large distances.•Horizontal movement, Pressure belt system provide them the pressure gradient•Corilis force modify their direction

Planetary winds

•The winds move towards equatorial low pressure = ITCZ• ITCZ – inter tropical convergence zone, where wind converges•Their direction is east to west due to coriolis force

Trade winds

•Tropical easterlies flows– east to west•Wind becomes dry when they reaches the western coast of the continents•Off –shore trade winds•Trade wind deserts

Tropical deserts and trade winds

•2nd•Cold currents provide desiccating effect to trade wind deserts•Cold current flow on western margins of continents

Tropical desert and cold currents

Mains2013

Q. Major hot deserts in northern hemisphere are located between 20-30 degree North latitudes and on the western side of the continents. Why? (10)

UPSC

Question

•From west to east•From STHP to SPLP

Westerlies

•From west to east•From STHP to SPLP•Less landmass in southern hemisphere•Fast flowing winds in the open sea •Roaring 40s, furious 50s, shrinking 60s and screaming 70s

Westerlies

Prelims2011

Q. Westerlies in southern hemisphere are stronger and persistent than northern hemisphere. Why?1. Southern hemisphere has less

landmass as compared to northern hemisphere

2. Coriolis force is higher in southern hemisphere as compared to northern hemisphere

Ans. 1 is correct, 2 is wrong

UPSC

Question

•From east to west•From poles to SPLP

Polar Easterlies

Summer Winter

Apparent movement of the sun

Summer Winter

movement of the pressure system

winds

Permanent wind

Planetary winds

Variable wind

Seasonal winds

Local winds

Mt.-valley breeze

Land-sea breeze

Wind system of the world

•Monsoon winds: seasonal reversal of winds•Feature of tropical latitude• In winter – trade wind blows north to south, in summer – trade wind blows south to north [but in limited area]

Seasonal winds

•Due to apparent northward movement of the sun in summer. Thus, the ITCZ (LP) also moves upward•Thus, the area which was under northern trade winds in winter, will come under southern trade winds in the summer

Monson winds

winds

Permanent wind

Planetary winds

Variable wind

Seasonal winds

Local winds

Mt.-valley breeze

Land-sea breeze

Wind system of the world

Cold wind

country windGreece GragaleItaly TremontaAdriatic sea

bora

Mountains WindAlps FohnRockies ChinookAndes Zonda

Warm winds

Local winds : mountains winds

Cold wind: land

HP condition in winter

Divergence of cold air

Siberia – BuranCanada - Blizzard

desert WindsSahara SiroccoEgypt KhamsinLibya GibliGulf of Guinea

Harmattan

Warm wind: desert

Local winds : land

summer

Hot-dusty wind = ‘loo’

states WindBihar, WB, Assam

Kalbaishakhi

KN Blossom shower

KR Mango shower

Pre-monsoon thunderstorm

Local winds: India

winds

Permanent wind

Planetary winds

Variable wind

Seasonal winds

Local winds

Mt.-valley breeze

Land-sea breeze

Wind system of the world

•During night time: top gets cooler than valley = HP, valley =LP•Wind move hill-top to valley => mountain breeze•Agriculture –frost bite, chill in habitation in the valley

Mountain breeze

•During day time: top gets warmer than valley = LP, valley = HP•So wind moves from valley to the top => valley breeze

Valley breeze

winds

Permanent wind

Planetary winds

Variable wind

Seasonal winds

Local winds

Mt.-valley breeze

Land-sea breeze

Wind system of the world

Land breezes

•Differential cooling of land and water•During night: • land cooler =HP, •water =LP•Wind move land to water => land breeze

Sea-breeze

•During day time: • land gets warmer =>LP , water =HP•Wind move from water to land => sea breeze

Pressure belts of the worldPlanetary wind systemVariable windsSeasonal, local windsMountain- valley breezeLand-sea breeze

•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

•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

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

Permanent jet stream

Temporary jet stream

Jet streams

• 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

• 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

• 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 =frontal rainfall

Cold front

• 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

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

Frontal cyclone

1) Intense LP system2)Air converges

towards the centre3)Closed isobars 4)In Northern

hemisphere convergence – anti-clockwise

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 wetserlies •Gradual movement- Predictable weather

Path of the temperate cyclone

Distribution of temperate cyclones

Hurricane –N. AmericaTyphoon - China•Late summer • Increased sea surface temperature = LP•Convergence of air around LP zone•Rising moist (wet) air => absolute instability

Tropical cyclone

•Cloud formation =more and more moisture – latent heat of evaporation => cumulo nimbus cloud => cyclone•Coriolis force induce spiral movement of air

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• 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