geo l5 oceanography_part2_0.2
TRANSCRIPT
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OceanographyClimatology
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Topics under Oceanography
Ocean Bottom Relief
Ocean Currents
Ocean Tide
coral reef
Temperature of Oceans
Salinity of Oceans
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Ocean bottom relief
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petroleum Sulphur
Resources from continental shelf
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Placer deposit Pearls, fish, calcium
Resources from continental shelf
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Continental slope Continental rise
Continental margins
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Poly-metallic nodules Indian exploration
Abyssal plain
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Continental Islands Volcanic islands
Types of Islands
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Sand-bar islands Coral Islands
Types of Islands
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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
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Coral bleaching
Coral polyps expel xooxanthalae under stress condition
Global warmingOzone depletionOcean acidificationSedimentationMarine pollutiondiseases
Reasons for bleaching
Coral reef
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•Fringing reef – barrier reef- atoll•Subsidence theory of Darwin•Standstill theory of Murray
Formation of coral reef
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Horizontal •waves•currents
Vertical •tides•Up-welling
Motion of Ocean water
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waves Ocean currents
Horizontal motion of ocean water
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tides Spring-neap tide
Tides
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Upwelling Down-welling
Up-welling and down-welling
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Temperature of the ocean
Salinity of the ocean
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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
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•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
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•Hemispheric variation•Northern hemisphere warmer than southern•Reason: large land mass in northern hemisphere – high energy
Temperature pattern of the Oceans
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•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
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•Ocean currents•Warm ocean current –warming effect•Cold ocean current cooling effect
Temperature pattern of the Oceans
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•Up-welling and dow-welling•Upwelling bring cool water from depth –lower down the surface temp
Temperature pattern of the Oceans
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•Down-welling – piling up of warm water – increase the temp
Temperature pattern of the Oceans
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•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
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•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
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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
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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
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1st layer – upto 500m(20-25 deg C)2nd layer – thermocline 500-1000m 3th layer – cold layer –beyond 1000m
Vertical distribution of temperature
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•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
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Temperature of the ocean
Salinity of the ocean
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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
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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
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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
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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
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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
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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
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•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
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•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
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•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
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•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
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•3th – inflow of large rivers• Ganga – Brahmaputra flow into Bay of Bengal•Bay of Bengal less saline than Arabian sea
Local Variations in Salinity
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Mississippi in G.of Mexico
Amu darya, Syr darya to Aral sea
Rivers inflow to the seas
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Black sea Persian gulf
Rivers inflow to the seas
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•4th – glaciers•Baltic sea receive fresh water from melting of glaciers – low salinity
Local Variations in Salinity
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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
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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
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Temperature of ocean watervariationsSalinity of ocean waterSalt budgetvariations
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Climatology
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•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
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•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
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Gas ProportionNitrogen 78%Oxygen 21%Argon 0.93%Carbon dioxide 0.03%Neon 0.0018%Helium 0.00005%ozone 0.00006%
Proportion of gases
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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
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Structure of atmosphere
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•90% of atmosphere within 32 km•Tropopause = Height 8 km at poles, 18 km at equator•At equator cumulonimbus clouds
Troposphere
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•Temperature decrease as height increases•Transparent to insolation (shortwave)•Heated by terrestrial radiation (longwave)•GHGs absorbs long wave terrestrial radiation
Greenhouse effect in troposphere
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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
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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
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•Temperature increases with height•Because of the presence of ozone layer•Ozone absorbs UV rays from isolation
stratosphere
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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
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•Absence of GHGs•Temperature decreases with height
Mesosphere
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Mesospheric clouds•Clouds visible at high latitudes•During summer season •Condensation of mixture of meteoric dust and some moisture
Noctilucent clouds
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•Temperature increase with height•Gases in ionic state – trap insolation – extremely hot•But ions are highly dispersed•Up to 800 km from earth
Thermosphere
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•From 80km to 640 km•Number of ionic layers•Useful in radio-communication
Ionosphere
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•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
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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
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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
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•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
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•Glowing lights at mid-nights at high latitudes•At height of exosphere and magnetosphere
Aurora
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•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
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•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
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•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
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•First 35% absorbed by Ozone layer•Then 15% by cloud cover•Only 50% energy reached to the earth surface
Heat budget - Incoming
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•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
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•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
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surface AlbedoFresh snow 80%-90%Desert 35-45%Grasses 26%Crops 15%Brick - concrete 10-20%
Albedo - table
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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
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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
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•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
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•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
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Low pressure – High pressure
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•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
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• 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
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• 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
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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
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•Normally, with increasing height temperature of air decreasing, but reverse is happened than it is called temperature inversion
Temperature Inversion
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•1st •At Tropopause – temperature starts increasing from here•So air packet reach till here, start moving downwards
Ex. Of temperature Inversion
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•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
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•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
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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
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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
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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
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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
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Mist
Haze Fog Sm
og
Decreasing level of visibility
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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
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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).
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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
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Prelims2013
Photochemical smog:NO2, Ozone + sunlight
Ans. A)
UPSC
Question
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Structure of atmosphereVertical Movement of airAdiabatic lapse rateTemperature inversion and its effects
fog
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evaporation Humidity condensation Precipitation
precipitation
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1) High temperature2) LP conditions3) Fast moving wind•Water vapour evaporate from the water body•Evaporation adds moisture in the air
Evaporation
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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
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•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
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Types of clouds
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Convectional rainfall Orographic rainfall
Types of rainfall
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Cyclonic rainfall Frontal rainfall
Types of rainfall
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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
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•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
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Equatorial LP belt
•Constant insolation•Air gets warm -LP•Air move upward -> cloud formation -> instability -> rain in the evening daily•Cumulonimbus clouds•Convectional rainfall
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Equatorial LP belt
•Absence of advection of air•Belt of calm / Doldrum•Because light, feeble winds - calm region
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•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)
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•As descending air – HP•Dynamically induced HP•Called ‘horse latitude’
Sub-tropical HP belt (STHP)
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•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)
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•Air risen at SPLP, descends at poles•High pressure conditions•Thermally induced
Polar high
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winds
Permanent wind
Planetary winds
Variable wind
Seasonal winds
Local winds
Mt.-valley breeze
Land-sea breeze
Wind system of the world
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•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
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•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
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•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
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•2nd•Cold currents provide desiccating effect to trade wind deserts•Cold current flow on western margins of continents
Tropical desert and cold currents
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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
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•From west to east•From STHP to SPLP
Westerlies
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•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
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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
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•From east to west•From poles to SPLP
Polar Easterlies
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Summer Winter
Apparent movement of the sun
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Summer Winter
movement of the pressure system
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winds
Permanent wind
Planetary winds
Variable wind
Seasonal winds
Local winds
Mt.-valley breeze
Land-sea breeze
Wind system of the world
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•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
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•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
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winds
Permanent wind
Planetary winds
Variable wind
Seasonal winds
Local winds
Mt.-valley breeze
Land-sea breeze
Wind system of the world
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Cold wind
country windGreece GragaleItaly TremontaAdriatic sea
bora
Mountains WindAlps FohnRockies ChinookAndes Zonda
Warm winds
Local winds : mountains winds
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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
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summer
Hot-dusty wind = ‘loo’
states WindBihar, WB, Assam
Kalbaishakhi
KN Blossom shower
KR Mango shower
Pre-monsoon thunderstorm
Local winds: India
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winds
Permanent wind
Planetary winds
Variable wind
Seasonal winds
Local winds
Mt.-valley breeze
Land-sea breeze
Wind system of the world
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•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
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•During day time: top gets warmer than valley = LP, valley = HP•So wind moves from valley to the top => valley breeze
Valley breeze
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winds
Permanent wind
Planetary winds
Variable wind
Seasonal winds
Local winds
Mt.-valley breeze
Land-sea breeze
Wind system of the world
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Land breezes
•Differential cooling of land and water•During night: • land cooler =HP, •water =LP•Wind move land to water => land breeze
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Sea-breeze
•During day time: • land gets warmer =>LP , water =HP•Wind move from water to land => sea breeze
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Pressure belts of the worldPlanetary wind systemVariable windsSeasonal, local windsMountain- valley breezeLand-sea breeze
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•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
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•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
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Westerlies winds
•The upper tropospheric winds / geo-strophic winds blow from west to east at the very high speed
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•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
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• In westerlies, there are strong, narrow bands of high speed wind => Jet stream•Speed of Jet stream 300kmph
Jet streams
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•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
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Permanent jet stream
Temporary jet stream
Jet streams
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• Jet stream embedded in westerlies (Rossby waves) at high latitude, cause pressure variability•That’s why they are called travelling depression
Jet streams
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Jet Stream – travelling depressions
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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
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• 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
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•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
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•Air masses do not stay at their source regions forever, they move out. While moving they came across other air masses.
Air masses
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•The relative difference between temperature and moisture decide their interaction with one another•The border/ meeting region of the two air-mass => Front
Front
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• 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
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• 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
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Fronts
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•Also called as extra-tropical cyclone, travelling depressions, cold-core cyclone, wave cyclones
Frontal cyclone
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1) Intense LP system2)Air converges
towards the centre3)Closed isobars 4)In Northern
hemisphere convergence – anti-clockwise
Meaning of cyclone
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Normal isobar Closed isobar
Isobar
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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
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•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
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Location of air masses Circular movement
Formative stage of frontal cyclone
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•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
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Interaction of air masses LP – closed isobars
Mature stage
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• 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
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•Frontolysis – no great temperature difference between two cold air masses – front dissipated – LP reduced – cyclone dissipated
Dissipation of frontal cyclone
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Stationary front Front
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Occluded front Frontolysis
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•Always west to east direction•Because influence of the wetserlies •Gradual movement- Predictable weather
Path of the temperate cyclone
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Distribution of temperate cyclones
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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
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•Cloud formation =more and more moisture – latent heat of evaporation => cumulo nimbus cloud => cyclone•Coriolis force induce spiral movement of air
Tropical cyclone
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• Intensification of LP•Converging air near water surface•Circulating air rises above (coriolis force)•Diverging air at the top of cyclone
Mature Tropical cyclone
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•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
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•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
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Distribution of tropical cyclone
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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
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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
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Mains2014
Q. Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why? (10)
UPSC
Question
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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
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