1. Clouds, Cirrus, and the Climate “Who are these that fly as a cloud, And as the doves to their window?” “Wer sind die, die heranfliegen wie Wolken, Wie Tauben zu irhem Schlag?” (Jesaja 60:8)

2. 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

3. CLOUD RADIATIVE FORCING General Avenues of Effect –Cloud Temperature –Albedo –Absorptivity/Emissivity –Cloud Cover –Cloud Layer Latitude (Hartmann, 1994)

4. CLOUD FEEDBACKS I Net Radiative Flux at TOA Sensitivity of Surface Temperature to CO 2 Then But…

5. CLOUD FEEDBACKS II Therefore: Where u i ’s are Cloud-Related Parameters UNCLE! (Paltridge, 1980)

6. CLOUD FEEDBACKS IIV Cloud Temperature--Emissivity Cloud Temperature--Surface Albedo Surface Albedo--Surface Temperature Consider Some Known Feedbacks: Cloud Water Path--Albedo/Emissivity Cloud Water Path--Albedo/Emissivity

7. RADIATIVE FORCING DEPENDS UPON CLOUD 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

8. CLOUD MODEL RESULTS (Stephens and Webster, 1980) Cirrus Result in Warmer Surface Temperature (Cloud-Free Temp = 280K)Cirrus Result in Warmer Surface Temperature (Cloud-Free Temp = 280K) Cooler Cloud Tops Result in Lower Net Flux out of Cloud Top than Net Flux into Cloud BottomCooler Cloud Tops Result in Lower Net Flux out of Cloud Top than Net Flux into Cloud Bottom

9. CLOUD MODEL RESULTS (Stephens and Webster, 1980) Variation Of Surface Temperature WRT Cloud Cover (Linear?)Variation Of Surface Temperature WRT Cloud Cover (Linear?) Opposite Effects for Low- and Mid- level Clouds than for CirrusOpposite Effects for Low- and Mid- level Clouds than for Cirrus Related to Height and Cloud-top TemperatureRelated to Height and Cloud-top Temperature

10. CLOUD MODEL RESULTS (Stephens and Webster, 1980) Albedo Stronger Function of Water Path than EmittanceAlbedo Stronger Function of Water Path than Emittance Water Path Variations More Important For More Tenuous CloudsWater Path Variations More Important For More Tenuous Clouds

11. CLOUD MODEL RESULTS (Stephens and Webster, 1980) Albedo Function of Both Cloud Water Path and Zenith AngleAlbedo Function of Both Cloud Water Path and Zenith Angle

12. CLOUD MODEL RESULTS (Stephens and Webster, 1980) Three Types of Clouds, Surface Temperature as Function of CWP and LatitudeThree Types of Clouds, Surface Temperature as Function of CWP and Latitude Small CWP, Heating Due to Emissivity Overwhelming Albedo--Tenuous Cirrus Have Smaller CWPSmall CWP, Heating Due to Emissivity Overwhelming Albedo--Tenuous Cirrus Have Smaller CWP Lower Clouds: Higher Temperature, Less HeatingLower Clouds: Higher Temperature, Less Heating High Latitude, Small Insolation, LW Effects Dominate SW EffectsHigh Latitude, Small Insolation, LW Effects Dominate SW Effects

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

14. SOME DIFFICULTIES 1)Poorly Understood Feedbacks 2)Feedbacks Not Really Implemented in Model-- Other Things are not Equal 3)Cirrus Radiative Properties not Fully Understood 4)Clouds Must be Parameterized a)Due to Model Resolution b)Math Description of Sub- Cell Processes 5)Incomplete Understanding of Cirrus Microphysics

15. WHERE TO NOW? CURRENT EFFORTS A Recent Parameterization (Stephens et al, 1990

16. WHERE TO NOW? FUTURE WORK (Mace 2002) ARMARM –MMCR,MPL,AERI The A-TrainThe A-Train –Not the Duke Ellington song (http://www.empire.k12.ca.us/capist rano/Mike/capmusic/modern/ameri can%20composers/ellington/ellingt o.htm) –Constellation (http://www.nasa.gov/images/conte nt/119021main3_A-Train- CALIPSO.jpg)

17. A Cloud withdrew from the Sky Superior Glory be But that Cloud and its Auxiliaries Are forever lost to me Had I but further scanned Had I secured the Glow In an Hermetic Memory It had availed me now Never to pass the Angel With a glance and Bow Till I am firm in Heaven Is my intention now. (Emily Dickenson ) To Study the Subtle and the Sublime

18. THANK YOU! I will be happy to hear any questions “As the clouds the clouds chase; And we go, And we drop like the fruits of the tree, Even we, Even so.” (George Meredith)