Clouds, Cirrus, and Clouds, Cirrus, and the Climatethe Climate

““Who are these that fly as a cloud,Who are these that fly as a cloud,

And as the doves to their window?”And as the doves to their window?”

““Wer sind die, die heranfliegen wie Wolken,Wer sind die, die heranfliegen wie Wolken,Wie Tauben zu irhem Schlag?”Wie Tauben zu irhem Schlag?”

(Jesaja 60:8)(Jesaja 60:8)

OUTLINE

• Cloud Effects– Cloud Radiative Forcing– General Feedbacks

• The Recondite Cirrus– Low- and Mid-level Clouds– Cirrus Clouds

• Addressing a Problem– Four Difficulties– Current Efforts– Future Work

CLOUD RADIATIVE FORCING

•General Avenues of Effect–Cloud Temperature

–Albedo

–Absorptivity/Emissivity

–Cloud Cover

–Cloud Layer Latitude

€

ΔR = ΔSabs − ΔF↑TOA

€

ΔR = ΔSabs − ΔF↑TOA (Hartmann, 1994)

CLOUD FEEDBACKS INet Radiative Flux at TOA

€

dT

dC=

dT

dF ↓N

dF ↓N

dC

€

F ↓N

€

F ↓N

€

dT

dC

€

dT

dCSensitivity of Surface Temperature to CO2

Then

But…

CLOUD FEEDBACKS II

Therefore:

€

dT

dC=

dT

dF ↓N

∂F ↓N

∂C1−

dT

dF ↓

∂F ↓

∂ui

dui

dT∑

⎡

⎣ ⎢

⎤

⎦ ⎥

−1

€

dF ↓N

dC=

∂F ↓

∂C+

∂F ↓

∂ui

dui

dT

dT

dC∑

Where ui’s are Cloud-Related Parameters

UNCLE!(Paltridge, 1980)

CLOUD FEEDBACKS IIV

•Cloud Temperature--Emissivity•Cloud Temperature--Surface Albedo•Surface Albedo--Surface Temperature

Consider Some Known Feedbacks:Consider Some Known Feedbacks:•Cloud Water Path--Albedo/EmissivityCloud Water Path--Albedo/Emissivity

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WaterPath (gm /m2) = ρw,idz0

∞

∫

RADIATIVE FORCING RADIATIVE FORCING DEPENDS UPON DEPENDS UPON

CLOUD TYPECLOUD TYPE

•Model-Run ExperimentsModel-Run Experiments

•Vary One Parameter at a TimeVary One Parameter at a Time

•Low- and Mid-level CloudsLow- and Mid-level Clouds

•Cirrus CloudsCirrus Clouds

CLOUD MODEL RESULTSCLOUD MODEL RESULTS(Stephens and Webster, 1980)(Stephens and Webster, 1980)

• Cirrus Result in Cirrus Result in Warmer Surface Warmer Surface Temperature Temperature (Cloud-Free Temp (Cloud-Free Temp = 280K)= 280K)

• Cooler Cloud Tops Cooler Cloud Tops Result in Lower Result in Lower Net Flux out of Net Flux out of Cloud Top than Net Cloud Top than Net Flux into Cloud Flux into Cloud BottomBottom

CLOUD MODEL RESULTSCLOUD MODEL RESULTS(Stephens and Webster, 1980)(Stephens and Webster, 1980)

• Variation Of Variation Of Surface Surface Temperature WRT Temperature WRT Cloud Cover Cloud Cover (Linear?)(Linear?)

• Opposite Effects Opposite Effects for Low- and Mid-for Low- and Mid-level Clouds than level Clouds than for Cirrusfor Cirrus

• Related to Height Related to Height and Cloud-top and Cloud-top TemperatureTemperature

CLOUD MODEL RESULTSCLOUD MODEL RESULTS(Stephens and Webster, 1980)(Stephens and Webster, 1980)

• Albedo Stronger Albedo Stronger Function of Water Function of Water Path than Path than EmittanceEmittance

• Water Path Water Path Variations More Variations More Important For More Important For More Tenuous CloudsTenuous Clouds

CLOUD MODEL RESULTSCLOUD MODEL RESULTS(Stephens and Webster, 1980)(Stephens and Webster, 1980)

• Albedo Function of Albedo Function of Both Cloud Water Both Cloud Water Path and Zenith Path and Zenith AngleAngle

CLOUD MODEL RESULTSCLOUD MODEL RESULTS(Stephens and Webster, 1980)(Stephens and Webster, 1980)

• Three Types of Clouds, Three Types of Clouds, Surface Temperature as Surface Temperature as Function of CWP and Function of CWP and LatitudeLatitude

• Small CWP, Heating Due to Small CWP, Heating Due to Emissivity Overwhelming Emissivity Overwhelming Albedo--Tenuous Cirrus Albedo--Tenuous Cirrus Have Smaller CWPHave Smaller CWP

• Lower Clouds: Higher Lower Clouds: Higher Temperature, Less HeatingTemperature, Less Heating

• High Latitude, Small High Latitude, Small Insolation, LW Effects Insolation, LW Effects Dominate SW EffectsDominate SW Effects

CONCLUSIONS ON CIRRUSCONCLUSIONS ON CIRRUS

•Changes in Optical Properties More Changes in Optical Properties More Important for Cirrus (Esp. Water Path Important for Cirrus (Esp. Water Path and Particle Size)and Particle Size)•At Lower Latitudes, May Contribute to At Lower Latitudes, May Contribute to Either Heating or to CoolingEither Heating or to Cooling•Effects Seem Less Certain than those Effects Seem Less Certain than those of Lower, Thicker Cloudsof Lower, Thicker Clouds

SOME DIFFICULTIESSOME DIFFICULTIES1)1) Poorly Understood Poorly Understood

FeedbacksFeedbacks2)2) Feedbacks Not Really Feedbacks Not Really

Implemented in Model--Implemented in Model--Other Things are not EqualOther Things are not Equal

3)3) Cirrus Radiative Properties Cirrus Radiative Properties not Fully Understoodnot Fully Understood

4)4) Clouds Must be Clouds Must be ParameterizedParameterizeda)a) Due to Model ResolutionDue to Model Resolutionb)b) Math Description of Sub-Math Description of Sub-

Cell ProcessesCell Processes

5)5) Incomplete Understanding Incomplete Understanding of Cirrus Microphysicsof Cirrus Microphysics

WHERE TO NOW? CURRENT EFFORTS

•A Recent Parameterization (Stephens et al, 1990

€

ε =1− exp −DKW( )

D = diffusivity

K = f (re )

W = IWP

α ext = f (PSD)

ω0 = f (IWP,PSD)

€

ε =1− exp −DKW( )

D = diffusivity

K = f (re )

W = IWP

α ext = f (PSD)

ω0 = f (IWP,PSD)

WHERE TO NOW? FUTURE WORK (Mace 2002)

• ARMARM– MMCR,MPL,AERIMMCR,MPL,AERI

• The A-TrainThe A-Train– Not the Duke Ellington Not the Duke Ellington

songsong (http://www.empire.k12.ca.us/capist(http://www.empire.k12.ca.us/capistrano/Mike/capmusic/modern/amerirano/Mike/capmusic/modern/american%20composers/ellington/can%20composers/ellington/ellingto.htm)ellingto.htm)

– ConstellationConstellation (http://www.nasa.gov/images/conte(http://www.nasa.gov/images/content/119021main3_A-Train-nt/119021main3_A-Train-CALIPSO.jpg)CALIPSO.jpg)

A Cloud withdrew from the SkySuperior Glory be

But that Cloud and its AuxiliariesAre forever lost to me

Had I but further scannedHad I secured the GlowIn an Hermetic MemoryIt had availed me now

Never to pass the AngelWith a glance and BowTill I am firm in Heaven

Is my intention now.(Emily Dickenson)

To Study the Subtle and the Sublime

THANK YOU!THANK YOU!I will be happy to hear any questionsI will be happy to hear any questions

““As the clouds the clouds As the clouds the clouds chase;chase;

And we go,And we go,And we drop like the fruits of And we drop like the fruits of

the tree,the tree,Even we, Even we, Even so.”Even so.”

(George Meredith)(George Meredith)