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Clouds and Radiation

Clouds and Radiation. “..there are substantial uncertainties in decadal trends in all data sets and at present there is no clear consensus on changes in total cloudiness over decadal time scales.” IPCC-The Scientific Basis-Chapter 3, p. 277.

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Clouds and Radiation

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  1. Clouds and Radiation “..there are substantial uncertainties in decadal trends in all data sets and at present there is no clear consensus on changes in total cloudiness over decadal time scales.” IPCC-The Scientific Basis-Chapter 3, p. 277 There has been an increase in clouds and precipitation, which reduce solar radiation available for actual and potential evapotranspiration but also increase soil moisture and make the actual evapotranspiration closer to the potential evapotranspiration. An increase in both clouds and precipitation has occurred over many parts of the land surface (Dai et al., 1999, 2004a, 2006), although not in the tropics and subtropics (which dominate the global land mean; Section 3.3.2.2). IPCC-The Scientific Basis-Chapter 3, p. 279

  2. IPCC WG1 AR4 Report Variability caused by model representations of clouds

  3. How do Clouds Alter the State of the Atmospheric Column? Diabatic Heating Profiles • Latent Heating • Condensation (warming) • Evaporation (cooling) • Net column latent heating = Precipitation mass * L • where L = latent heat • Radiative Heating • Incoming solar • Outgoing IR • Net column radiative heating= net incoming minus net outgoing • Profiles of diabatic heating impact atmospheric dynamic and thermodynamic structure

  4. Radiative Flux Divergence Primer Reflected SW Insolation OLR Incoming – Outgoing= net radiation into column TOA • Radiative Flux Divergence = net radiation into column - net radiation into surface • positive values imply heating • negative values imply cooling Upwelling and Downwelling SW and LW Surface Downwelling–Upwelling= net radiation into surface

  5. Radiative Heating Rate Profile Reflected SW Insolation OLR TOA • positive values imply heating • negative values imply cooling Upwelling and Downwelling SW and LW Surface neg pos NET

  6. What Cloud Properties Change the Radiative Heating Rate Profile? • Amount of the sky that contains cloud • Thickness of individual clouds and layers • Height in the atmosphere • Composition • Contain ice crystals, liquid water, or both? • Particle sizes? • Particle concentrations?

  7. How Does the Location of Cloud Impact the Surface Temperature? Space High Clouds ~10-km Low Clouds ~2-km COOLING WARMING

  8. Cirrus and Cumulus from the Space Shuttle Courtesy NASA CERES

  9. Figure 2.10 • IPCC Working Group I (2007)

  10. Representing Clouds in Climate Models CLIMATE MODEL GRID CELL 60-N Weather Forecast Model Grid Cell Cloud Resolving Models: Less Than Width Of Lines 55-N 172-W 157-W

  11. Clouds and Radiation Through a Soda Straw

  12. 2-km CloudsThrough a SODASTRAW! Meteorological Tower Multiple Radars Calibration Facility Multiple Lidars Surface Radiation

  13. What types of remote sensors do we use to make cloud measurements? • Visible and Infrared Sky Imagers • Vertically-Pointing Lasers (LIDARs) • Measure the height of the lowest cloud base • Below cloud concentrations of aerosol and water vapor • Beam quickly disperses inside cloud • Cloud Radars • cloud location and microphysical composition • In-cloud updrafts, downdrafts, and turbulence • Microwave Radiometers • Measure the total amount of liquid water in atmosphere • Can’t determine location of liquid • Presently not measuring total ice content

  14. Visual Images of the Sky • cloud coverage (versus cloud fraction) • simple! digitize images and … • daytime only • integrated quantity

  15. Laser Data from Southern Great Plains 20-km No Signal 10-km Low Clouds Ice Clouds Surface time 7:00 pm 7:00 am 24 Hours 7:00 pm Negligible Return Cloud and Aerosol Particles Cloud droplets

  16. Niamey, Niger, Africa • 20 Cloud Droplets • 15 Cloud and/or Aerosol Height (km) • 10 • LIQUID CLOUDS • 5 • Biomass Burning • Dust Negligible Return • 0 • 1200 • 0000 • 0000 Time (UTC)

  17. 3.2 mm cloud radars 8 mm UHF 10 cm VHF

  18. 94 GHz 35 GHz Maximum Propagation Distance Energy Absorbed by Atmosphere 10-15 km 20-30 km 3.2 mm 8 mm Radar Wavelength

  19. The DOE ARM Cloud Radars

  20. Cloud Radar Data from Southern Great Plains 20-km Black Dots: Laser Measurements Of Cloud Base Height 10-km Surface time 7:00 pm 7:00 am 7:00 pm Small Cloud Particles Typical Cloud Particles Very Light Precipitation

  21. Cloud Radar Data from Southern Great Plains 20-km Black Dots: Laser Measurements Of Cloud Base Height 10-km Insects Thin Clouds Surface time 7:00 pm 7:00 am 7:00 pm Small Cloud Particles Typical Cloud Particles Very Light Precipitation

  22. Evolution of Cloud Radar Science • Cloud Structure and Processes • Cloud Statistics • Cloud Composition

  23. Top Radar Echo Low Radar Sensitivity 10-km Base Radar Echo Top Base 2-km Emission Radar Echo Surface Microwave Radiometer Laser Radar

  24. GFS cloud initialization data • mandatory radiosonde data • satellite retrievals of temperature • satellite-derived cloud motion vector • aircraft • cloud fraction parameterization: Xu and Randall (1996) • August • GFS 10-15 km cloud fraction larger than AMF • AMF 0-10 km cloud fraction larger than GFS Height (km) Cloud Fraction (%) Kollias, P, M.A. Miller, K.Johnson, M. Jensen, D. Troyan, 2008

  25. Liquid Cloud Particle Mode Radius 6 4 Height (km) 2 0 time 7:00 pm 7:00 am 7:00 pm 25 17 1 4 10 Micrometers Miller and Johnson, 2003

  26. Tobin et al., 2007

  27. Clouds and Radiation From Space

  28. A-TRAIN CONSTELLATION The Afternoon or "A-Train" satellite constellation presently consists of 5 satellites Two additional satellites, OCO and Glory, were supposed to join the constellation OCO was lost during a launch failure on 2/24/2009. Glory is scheduled to launch (10/01/10) Approx equator crossing times

  29. Aqua CALIPSO Aura Glory? OCO CloudSat PARASOL OMI - Cloud heights OMI & HIRLDS – Aerosols MLS& TES - H2O & temp profiles MLS & HIRDLS – Cirrus clouds CALIPSO- Aerosol and cloud heights Cloudsat - cloud droplets PARASOL - aerosol and cloud polarization OCO - CO2 MODIS/ CERES IR Properties of Clouds AIRS Temperature and H2O Sounding (Source: M. Schoeberl) Afternoon Constellation Coincidental Observations

  30. CloudSat (Hurricane Ike)

  31. CloudSat

  32. Radar/Lidar Combined Product Development • Formation flying is a key design element in cloudsat • CloudSat has demonstrated formation flying as a practical observing strategy for EO. • Overlap of the CloudSat footprint and the CALIPSO footprint, within 15 seconds, is achieved >90% of the time.

  33. lidar/radar combined ice microphysics - new A-Train ice cloud microphysics Preliminary example from Zhien

  34. A-Train Cloud Ice MLS ECMWF CloudSat

  35. What We Know About Solar Radiation and Clouds Solid theoretical foundation for interaction between a single, spherical liquid cloud droplet and sunlight and populations of spherical droplets. Cloud Droplet Sun Scattered Light

  36. What We Know About Solar Radiation and Clouds • Some theoretical foundation for interaction of sunlight and simple ice crystal shapes

  37. The Real World

  38. What We Wish We Knew About Solar Radiation and Clouds • How do we compute the total impact of a huge collection of diverse individual cloud particles? • What are the regional differences in cloud composition, coverage, thickness, and location in the atmosphere? • If we knew (1) and (2), how do we summarize all of this information so that it can be incorporated into a climate model?

  39. What We Know About Outgoing Terrestrial Radiation and Clouds • Good theoretical foundation for interaction of terrestrial radiation and cloud water content (liquid clouds). • Particle: • radius somewhat important in thin liquid clouds • shape and size somewhat important in high level ice clouds (cirrus) • Aerosols?

  40. Miller and Slingo, 2007

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