Major Forms of Major Forms of CondensationCondensation

What are the forms of What are the forms of condensation?condensation?

CloudCloud FogFog Frost and DewFrost and Dew

Differences between Forms of Differences between Forms of CondensationCondensation

Cloud, fog, frost and dew??Cloud, fog, frost and dew??– CloudCloud high in the skyhigh in the sky– fogfog near the surface of the near the surface of the

earthearth– frost and dewfrost and dew at the surface of the earthat the surface of the earth

Similar in FormationSimilar in Formation

Cooling (Temperature drops)Cooling (Temperature drops) Air holds less waterAir holds less water RH increasesRH increases When RH = 100%, moisture When RH = 100%, moisture

releasedreleased

Frost at 22/12/1999Frost at 22/12/1999

FROST & DEWFROST & DEW

Frost againFrost again

Dew at Spider WebDew at Spider Web

What is the difference What is the difference between Dew and Frost?between Dew and Frost?

–Dew: Dew: dew point > 0dew point > 0CC–Frost:Frost: dew point dew point 0 0 CC

FOGFOG

Radiation Fog (Conditions)Radiation Fog (Conditions) Clear skyClear sky high RHhigh RH temperature inversiontemperature inversion calm and still aircalm and still air presence of depression or hollowpresence of depression or hollow

Advection FogAdvection Fog

Advection FogAdvection Fog

Frontal FogFrontal Fog

Steam FogSteam Fog

Upslope FogUpslope Fog

CLOUDCLOUD

PrecipitationPrecipitation

Water droplets from condensation Water droplets from condensation is very small in size – is very small in size – 0.1 mm0.1 mm

Raindrops are much larger – Raindrops are much larger – 0.5-0.5-2.0 mm2.0 mm

The main difference between The main difference between condensation and precipitation is condensation and precipitation is the the sizesize of water droplets of water droplets

Formation ProcessesFormation Processes Air coolingAir cooling Condensation and cloud formationCondensation and cloud formation Accumulation of moistureAccumulation of moisture The growth of cloud dropletsThe growth of cloud droplets

Collision and Coalescence Collision and Coalescence In tropical and sub-tropical regionsIn tropical and sub-tropical regions Cloud top temperature : Cloud top temperature : warmer than -15warmer than -15ooCC Turbulence Mixing :Turbulence Mixing : Different size droplets move at different Different size droplets move at different

speedsspeeds cumulonimbuscumulonimbus

Collision and CoalescenceCollision and Coalescence

LargeWaterdroplet

Fall in higher speed

Fall in lower speed

Direct capture

wake capture

Ice-Crystal (Bergeron) ProcessIce-Crystal (Bergeron) Process

In higher latitudes (temperate regions)In higher latitudes (temperate regions) Super-cooled water – water droplets in Super-cooled water – water droplets in

cloud with temperature below 0cloud with temperature below 0ooCC Because of extremely small size of Because of extremely small size of

cloud dropletscloud droplets Insufficient freezing nucleiInsufficient freezing nuclei

Ice-Crystal (Bergeron) ProcessIce-Crystal (Bergeron) Process

Saturated Saturated vapour vapour pressure over pressure over super-cooled super-cooled water is water is greater than greater than that over icethat over ice

Ice-Crystal (Bergeron) ProcessIce-Crystal (Bergeron) Process

Air can be Air can be saturated for saturated for ice when it is ice when it is not saturated not saturated for waterfor water

Ice-Crystal (Bergeron) ProcessIce-Crystal (Bergeron) Process

Ice crystals Ice crystals grow at the grow at the expense of expense of cloud droplets cloud droplets until they are until they are large enough large enough to fallto fall

3 main types of precipitation3 main types of precipitation

Convection Convection RainRain

Cyclonic / Cyclonic / Frontal rainFrontal rain

Orographic Orographic / relief rain/ relief rain

Lifting Lifting mechanismmechanism

Real world Real world examplesexamples

Diagram of Diagram of formationformation

Low pressure system due to thermal nature

Warm air mass meets cold air mass

Uplifting along slopes

ITCZ Polar front Tai Mo Shan

Spatial Variation of rainfallSpatial Variation of rainfall There is more There is more

precipitation in precipitation in ocean than in ocean than in continent.continent.

ocean

continent

Spatial Variation of rainfallSpatial Variation of rainfall Primary Primary

maximum maximum occurs at a belt occurs at a belt between 10between 10ooN to N to 1010ooS in the S in the vicinity of the vicinity of the ITCZITCZ

ocean

continent

Spatial Variation of rainfallSpatial Variation of rainfall secondary secondary

maximum maximum occurs at a belt occurs at a belt between 40between 40oo to to 5555ooN&S in the N&S in the vicinity of the vicinity of the ITCZITCZ

ocean

continent

Spatial Variation of rainfallSpatial Variation of rainfall Primary minima Primary minima

find in latitudes find in latitudes higher than higher than 5555ooN&SN&S

Secondary Secondary minima in sub-minima in sub-tropical high tropical high pressure belts pressure belts (20(20oo-35-35ooN&S)N&S)

ocean

continent

Factors affecting the pattern of rainfallFactors affecting the pattern of rainfall Air pressureAir pressure Zones of convergence and divergenceZones of convergence and divergence Strong convection along low pressure Strong convection along low pressure

beltsbelts Uprising air leads to condensation and Uprising air leads to condensation and

cloud formationcloud formation Descending air along high pressure Descending air along high pressure

belts suppress condensationbelts suppress condensation

Describe and explain the factor that influence the pattern of rainfall from the diagram on the right.

0o

50oS

50oN

Zones of abundant rainfallZones of abundant rainfall Around the equatorial regionsAround the equatorial regions e.g. Amazon Basine.g. Amazon Basin Doldrum low pressureDoldrum low pressure Convergence of trade winds along Convergence of trade winds along

ITCZITCZ Intense solar radiation promotes strong Intense solar radiation promotes strong

convective upliftconvective uplift Ares dominated by warm moist Ares dominated by warm moist

equatorial marine air massesequatorial marine air masses

Zones of abundant rainfallZones of abundant rainfall Western sides in middle latitudesWestern sides in middle latitudes e.g. Western Coast of Canadae.g. Western Coast of Canada Under influences of the onshore Under influences of the onshore

westerlies and frequent frontal westerlies and frequent frontal cyclonescyclones

Western mountrains(Rockies and Western mountrains(Rockies and Andes) promote orographic influences Andes) promote orographic influences and heavy precipitationand heavy precipitation

Describe and explain the factor that influence the pattern of rainfall from the diagram on the right.

Zones of scanty rainfallZones of scanty rainfall Polar areas of North AmericaPolar areas of North America Air with low moisture content due to Air with low moisture content due to

low temperaturelow temperature Descending cold upper air masses Descending cold upper air masses

unfavourable for condensationunfavourable for condensation

Zones of scanty rainfallZones of scanty rainfall 1515oo-30-30ooS in the western side of South S in the western side of South

AmericaAmerica 3030oo-40-40ooN of south-western U.S.A.N of south-western U.S.A. Affected by sub-tropical anticyclone of Affected by sub-tropical anticyclone of

high pressurehigh pressure Rain-shadow effect of Rockies and Rain-shadow effect of Rockies and

AndesAndes