ATM OCN 100 Summer 2002 1 ATM OCN 100 - Summer 2002 LECTURE 11 (con’t.) FORMATION OF CLOUDS, FOG,...

MADISON’S CURRENT WEATHERMADISON’S CURRENT WEATHER

Madison Weather at 1000 AM CDT 15 JUL 2002 Updated twice an hour at :05 and :25 Sky/Weather: SUNNY Temperature: 80 F (26 C) Dew Point: 60 F (15 C) Relative Humidity: 50% Wind: VRB6 MPH Barometer: 30.12F (1019.10 mb)

ATM OCN 100 Summer 2002ATM OCN 100 Summer 2002 2929

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ATM OCN 100 - ATM OCN 100 - Summer 2002 Summer 2002 LECTURE 11LECTURE 11

FORMATION OF CLOUDS, FOG, FORMATION OF CLOUDS, FOG, DEW & FROSTDEW & FROST

A. INTRODUCTIONA. INTRODUCTION– What is a cloud?What is a cloud?– Historical PerspectiveHistorical Perspective– Why are clouds important?Why are clouds important?


BACKGROUND:BACKGROUND:CLOUDS, FOG, DEW & FROSTCLOUDS, FOG, DEW & FROST

CloudCloud– A visible aggregation of water droplets &/or A visible aggregation of water droplets &/or

ice crystals suspended in air above ground.ice crystals suspended in air above ground. FogFog

– A low-level cloud at ground level that A low-level cloud at ground level that reduces horizontal visibility.reduces horizontal visibility.

Dew & FrostDew & Frost– Surface condensation/deposition Surface condensation/deposition

phenomenaphenomena..


B. REQUIREMENTS FOR B. REQUIREMENTS FOR FORMATION of DROPLETSFORMATION of DROPLETS

Statement of Practical ProblemsStatement of Practical Problems Need for Saturation ConditionsNeed for Saturation Conditions Low-level Condensation Process in Low-level Condensation Process in

Dew FormationDew Formation Special Requirements in Free AirSpecial Requirements in Free Air Condensation Process in Cloud Condensation Process in Cloud

FormationFormation


C. MECHANISMS for CLOUD C. MECHANISMS for CLOUD (FOG, DEW (FOG, DEW oror FROST) FROST) FORMATIONFORMATION

To Saturate To Saturate – R.H. needs to reach 100% (or TR.H. needs to reach 100% (or Tairair = T = Tdewdew) )

Formation OptionsFormation Options– Add water vapor Add water vapor

(increase T (increase Tdewdew to T to Tairair ); );– Cool air Cool air

(reduce T (reduce Tairair to T to Tdewdew ). ). where... where...


OPTIONS TO SATURATE THE AIROPTIONS TO SATURATE THE AIR

Evaporation MechanismsEvaporation Mechanisms Adding water vapor to saturation Adding water vapor to saturation (increase dewpoint to air temperature)(increase dewpoint to air temperature)

– Require abundant liquid water source Require abundant liquid water source (e.g., ocean, lake, or lush vegetation) (e.g., ocean, lake, or lush vegetation);;

– Mix moisture upward from surface by air Mix moisture upward from surface by air motion.motion.


OPTIONS TO SATURATE THE AIROPTIONS TO SATURATE THE AIR (con’t.)(con’t.)

Cooling MechanismsCooling Mechanisms Cool air to saturation Cool air to saturation (reduce air temperature to dewpoint) (reduce air temperature to dewpoint)

by:by:

– Radiational Cooling Radiational Cooling – Expansional CoolingExpansional Cooling– Evaporative CoolingEvaporative Cooling– Advection Cooling - Horizontal TransportAdvection Cooling - Horizontal Transport


D. LOW LEVEL SATURATION D. LOW LEVEL SATURATION PROCESSES & PHENOMENAPROCESSES & PHENOMENA

Dew & FrostDew & Frost

– DefinitionsDefinitions

– FormationFormation

– Comparison & ContrastsComparison & Contrasts

– SignificanceSignificance


DewDew


HoarfrostHoarfrost


FrostFrost


E. CLOUD (E. CLOUD (oror FOG) FOG) FORMATION REQUIREMENTSFORMATION REQUIREMENTS

A Problem A Problem – Dipolar nature of water moleculesDipolar nature of water molecules– Leads to difficulty in condensing in Leads to difficulty in condensing in

clean airclean air SupersaturationSupersaturation

– Condition where R.H. > 100%.Condition where R.H. > 100%. Mechanism for CondensationMechanism for Condensation

Cloud Condensation Nuclei Cloud Condensation Nuclei


CLOUD CONDENSATION NUCLEICLOUD CONDENSATION NUCLEI

Provide sites for condensationProvide sites for condensation Requirement -Requirement -

– Hygroscopic Hygroscopic substances substances (Water loving) (Water loving)

Types of Condensation NucleiTypes of Condensation Nuclei– Sea saltSea salt– Combustion productsCombustion products– Anthropogenic substancesAnthropogenic substances


Aerosols from Sea SprayAerosols from Sea Spray


Aerosols from WildfiresAerosols from Wildfires


Aerosols from Urban PollutionAerosols from Urban Pollution


E. MECHANISMS for E. MECHANISMS for CLOUD or FOG FORMATION CLOUD or FOG FORMATION (con’t.)(con’t.)

Cooling Mechanisms

– Expansional Cooling

– Evaporative Cooling

– Advection Cooling - Horizontal Transport

– Radiational Cooling


Clouds accompanying a F-18 jet Clouds accompanying a F-18 jet breaking the Sound Barrierbreaking the Sound Barrier


EXPANSIONAL COOLING SPECIFICSEXPANSIONAL COOLING SPECIFICS

Review of adiabatic processesReview of adiabatic processes Dry adiabatic lapse rateDry adiabatic lapse rate

– NoNo H H22O phase change when O phase change when R.H. < 100%; R.H. < 100%;

– DALR DALR 10 C10 Coo per 1000 m per 1000 m (5.5 F (5.5 Foo per 1000 ft); per 1000 ft);

– Reversible processReversible process cooling by DALR during ascent = cooling by DALR during ascent = warming by DALR during descent. warming by DALR during descent.


Response of Ascent/Descent of Air Parcel:Response of Ascent/Descent of Air Parcel: Dry Adiabatic Lapse Rate Dry Adiabatic Lapse Rate

See Fig. 6.8 Moran & Morgan (1997)See Fig. 6.8 Moran & Morgan (1997)


Comparison of Dry & Saturation Comparison of Dry & Saturation (Moist) Adiabatic Lapse Rates(Moist) Adiabatic Lapse Rates See Fig. 6.9 Moran & Morgan (1997)See Fig. 6.9 Moran & Morgan (1997)


EXPANSIONAL COOLING SPECIFICS EXPANSIONAL COOLING SPECIFICS (con’t.)(con’t.)

Saturation (moist) adiabatic lapse rateSaturation (moist) adiabatic lapse rate– Involves HInvolves H22O phase change whenO phase change when

R.H. = 100%; R.H. = 100%;– Release of latent heat of condensation into parcel Release of latent heat of condensation into parcel

diminishes cooling effect by adiabatic expansion;diminishes cooling effect by adiabatic expansion;– SALR SALR 6 to 7 C6 to 7 Coo per 1000 m per 1000 m

(3 F (3 Foo per 1000 ft); per 1000 ft);– Process may Process may notnot be reversible. be reversible.


WAYS TO LIFT FORWAYS TO LIFT FOREXPANSIONAL COOLINGEXPANSIONAL COOLING

Dynamic LiftingDynamic Lifting

– In surface low pressure systems;In surface low pressure systems;– Along frontal surfaces.Along frontal surfaces.



Dynamic LiftingDynamic Lifting– In surface low pressure systems;In surface low pressure systems;– Along frontal surfaces.Along frontal surfaces.

Lifting by ConvectionLifting by Convection– Localized heatingLocalized heating– Ascending convection currentsAscending convection currents



Dynamic LiftingDynamic Lifting– In surface low pressure systems;In surface low pressure systems;– Along frontal surfaces.Along frontal surfaces.

Lifting by ConvectionLifting by Convection– Localized heatingLocalized heating– Ascending convection currentsAscending convection currents

Mechanical LiftingMechanical Lifting Over mountain barriersOver mountain barriers (or orographic lifting)(or orographic lifting)


AN EXAMPLEAN EXAMPLEAir Flow over a mountainAir Flow over a mountain


AN EXAMPLE AN EXAMPLE (con’.t)(con’.t) Lift unsaturated air to saturationLift unsaturated air to saturation


AN EXAMPLEAN EXAMPLE (con’.t)(con’.t) Lift saturated air to topLift saturated air to top


AN EXAMPLEAN EXAMPLE (con’.t)(con’.t) Force air to sinkForce air to sink


In RealityIn Reality

CloudsClouds Vegetation on upwind vs. downwind slopesVegetation on upwind vs. downwind slopes Special extreme examplesSpecial extreme examples

– Chinook WindsChinook Winds

– Santa Ana Winds Santa Ana Winds where…where…


Mountain Wave CloudsMountain Wave Clouds


IR Enhanced Satellite23 Oct 2001 7AM PDT

Clouds


Mountains Affect ClimateMountains Affect Climate


Forest vegetation on West Slopes Forest vegetation on West Slopes of Sierrasof Sierras (in Yosemite N.P., CA)(in Yosemite N.P., CA)


Arid Vegetation on East Slopes Arid Vegetation on East Slopes of Sierrasof Sierras (Owens Valley near Bishop, CA)(Owens Valley near Bishop, CA)


A Day out WestA Day out West

ChinookChinook

Santa AnaSanta Ana


Chinook WindsChinook Winds


Santa Ana WindsSanta Ana Winds


Effect of moisture on Stability Effect of moisture on Stability

Recall Stability vs. Instability Criteria Recall Stability vs. Instability Criteria for a dry air parcel ….for a dry air parcel ….


STABLE CONDITIONSSTABLE CONDITIONSCompare Compare EnvironmentEnvironment with with DALRDALR

Colder parcel sinks & returns to startColder parcel sinks & returns to start

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (m

)

Parcel is colder & Parcel is colder & more densemore dense

Environment is warmer & Environment is warmer & less denseless dense


UNSTABLE CONDITIONSUNSTABLE CONDITIONS

Compare Compare EnvironmentEnvironment with with DALRDALR Warmer parcel continues upward Warmer parcel continues upward

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (

m)

Parcel is warmer & Parcel is warmer & less denseless dense

Environment is colder Environment is colder & more dense& more dense


Effect of moisture on Stability Effect of moisture on Stability

Recall Stability vs. Instability Criteria Recall Stability vs. Instability Criteria for a dry air parcel …. for a dry air parcel ….

But now consider water vapor & But now consider water vapor & saturated air …saturated air …


ABSOLUTELY STABLE CONDITIONSABSOLUTELY STABLE CONDITIONSCompare Compare EnvironmentEnvironment with with SALRSALR & & DALRDALR


0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (

m)


UNSTABLE CONDITIONSUNSTABLE CONDITIONS

Compare Compare EnvironmentEnvironment with with DALRDALR Warmer parcel continues upward Warmer parcel continues upward

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (

m)


ABSOLUTELY UNSTABLE CONDITIONSABSOLUTELY UNSTABLE CONDITIONS

Compare Compare EnvironmentEnvironment with with SALRSALR & & DALRDALR Warmer parcel continues upwardWarmer parcel continues upward

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (

m)


If STABLE CONDITIONS for DryIf STABLE CONDITIONS for DryCompare Compare EnvironmentEnvironment with with DALRDALR


0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (

m)


But UNSTABLE CONDITIONS for HumidBut UNSTABLE CONDITIONS for HumidCompare Compare EnvironmentEnvironment with with SALRSALR Warmer parcel continues upwardWarmer parcel continues upward

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (

m)


CONDITIONALLY STABLE CONDITIONSCONDITIONALLY STABLE CONDITIONSCompare Compare EnvironmentEnvironment with with SALRSALR & & DALRDALR

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

TEMPERATURE (C)

AL

TIT

UD

E (

m)


Stability CriteriaStability CriteriaSee Fig. 6.14 Moran & Morgan (1997)See Fig. 6.14 Moran & Morgan (1997)

A.A. SuperadiabaticSuperadiabaticB.B. Conditionally Stable, Conditionally Stable,

Lapse Lapse C.C. Absolutely Stable, Absolutely Stable,

LapseLapseD.D. IsothermalIsothermalE.E. InversionInversion


F. LOW LEVEL SATURATION F. LOW LEVEL SATURATION PROCESSES & PHENOMENAPROCESSES & PHENOMENA

FogsFogs

– DefinitionDefinition

– Comparison between Fog & Clouds;Comparison between Fog & Clouds;

– Fog Formation MechanismsFog Formation Mechanisms cooling to saturationcooling to saturation addition of moistureaddition of moisture

– SignificanceSignificance


Fog over Sydney HarborFog over Sydney Harbor


FogFog

Fog is similar to a stratus cloud except that it touches the ground. It is not, necessarily formed in the same manner.


Surface Weather Map from an Autumn AM Surface Weather Map from an Autumn AM with with IsobarsIsobars & Fronts & Fronts


IFR – Instrument Flight RulesIFR – Instrument Flight Rules Red Dots: Ceiling < 1000 ft or Visibility < 3 milesRed Dots: Ceiling < 1000 ft or Visibility < 3 miles


FOGS FOGS (con’t.)(con’t.)

Fog ClassificationFog Classification

Fog types named eitherFog types named either

– by temperature; by temperature; oror

– by formation process.by formation process.

where...where...



Fog Type ClassificationFog Type Classification by by TemperatureTemperature– WARM FOGWARM FOG

contains liquid droplets, esp. T > 0 contains liquid droplets, esp. T > 0ooCC– COLD FOGCOLD FOG

contains supercooled liquid droplets contains supercooled liquid droplets with T < 0with T < 0ooC (but T > -30C (but T > -30ooC)C)

– ICE FOGICE FOG ( (oror ICE CRYSTAL FOG) ICE CRYSTAL FOG) contains ice crystals when T < -35 contains ice crystals when T < -35ooCC



Fog Type Classification by Fog Type Classification by Formation Process Formation Process

– How did the fog form?How did the fog form?

– With Following Examples…With Following Examples…


Radiation FogRadiation Fog (from (from The Weather DoctorThe Weather Doctor, K. C. Heidorn, PhD), K. C. Heidorn, PhD)


Radiation FogRadiation FogCool air by loss of IR radiationCool air by loss of IR radiation


Valley FogValley Fog (from (from The Weather DoctorThe Weather Doctor, K. C. Heidorn, PhD), K. C. Heidorn, PhD)


Radiation Fog (Radiation Fog (oror Valley Fog) Valley Fog)Cool air by IR radiation & cold air drainageCool air by IR radiation & cold air drainage


Upslope FogUpslope Fog(from (from The Weather DoctorThe Weather Doctor, K. C. Heidorn, PhD), K. C. Heidorn, PhD)


Upslope (Upslope (oror Mountain Fog) Mountain Fog)Cool air by expansion through liftingCool air by expansion through lifting


Advection FogAdvection Fog(from (from The Weather DoctorThe Weather Doctor, K. C. Heidorn, PhD), K. C. Heidorn, PhD)


Advection FogAdvection FogCool air by transport & contact with cold surfaceCool air by transport & contact with cold surface


Steam Fog (Steam Fog (oror Sea Smoke) Sea Smoke)Evaporation & saturation of airEvaporation & saturation of air


Steam & Radiation FogSteam & Radiation Fog Cooling along with evaporation to saturate airCooling along with evaporation to saturate air


Rain Fog Rain Fog (from (from The Weather DoctorThe Weather Doctor, K. C. Heidorn, PhD), K. C. Heidorn, PhD)


Rain FogRain FogEvaporation from falling rainEvaporation from falling rain



Fog Type Classification by Fog Type Classification by Formation Process Formation Process

– RADIATION FOGRADIATION FOG

– UPSLOPE FOG (UPSLOPE FOG (oror MOUNTAIN FOG) MOUNTAIN FOG)

– ADVECTION FOGADVECTION FOG

– STEAM FOG (STEAM FOG (oror SEA SMOKE) SEA SMOKE)

– RAIN FOGRAIN FOG

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ATM OCN 100 Summer 2002 1 ATM OCN 100 - Summer 2002 LECTURE 11 (con’t.) FORMATION OF CLOUDS, FOG,...

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