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Orbit Characteristics and View Angle Effects on the Global Cloud Field

Orbit Characteristics and View Angle Effects on the Global Cloud Field. Brent C. Maddux 1,2 Steven A. Ackerman 1 Steve Platnick 3 Paul Hubanks 4 1 Cooperative Institute for Meteorological Satellite Studies 2 Department of Atmospheric and Oceanic Sciences-U of Wisconsin

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Orbit Characteristics and View Angle Effects on the Global Cloud Field

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  1. Orbit Characteristics and View Angle Effects on the Global Cloud Field Brent C. Maddux1,2 Steven A. Ackerman1 Steve Platnick3 Paul Hubanks4 1Cooperative Institute for Meteorological Satellite Studies 2Department of Atmospheric and Oceanic Sciences-U of Wisconsin 3NASA Goddard Space Flight Center, Greenbelt, Maryland 4Wyle Information Systems, McLean, VA 22102

  2. Motivation • Comparison to other cloud datasets (apples-to-apples) • Place ‘error bars’ on global mean statistics • Quantify cloud variability globally

  3. Aqua 7 Year Mean Global Means • Daytime Cloud Fraction • Coast lines evident • Differences where expected: maritime stratocumulus decks, SH land, etc. Terra 9 Year Mean 0 .25 .5 .75 1.0

  4. Global Cloud Amount Anomaly MODIS Cloud Fraction Terra (Red) and Aqua (Black) 3 2 1 0 -1 -2 -3 CA Anomaly (%) 1970 1975 1980 1985 1990 1995 2000 2005 2010

  5. Cloud Fraction vs Viewing Angle • 7 years of Aqua and Terra • 16% increase from near nadir to edge of scan • View angle effect not constant for all cloud types Cloud Fraction (%) Cloud Fraction vs Sensor Zenith Angle Sensor Zenith Angle

  6. 0 .25 0.5 .75 1.0 Single Day in the MODIS Orbit Terra Daytime Cloud Fraction • Geostationary-like view • 16 day orbit procession • U-Shape at edges of convection and cloudy regions • Increase in pixel size with view angle

  7. Nadir to 10° Nadir to 10° minus 60 and greater 60° to edge of scan° Daytime Cloud Fraction Mean • Differences not uniform • Largest differences not where thin high clouds exist

  8. Near Nadir Near Edge of Scan Cloud Fraction (%) Nadir vs Edge of Scan • Changes are not uniform • Largest changes in CF aren’t the same as largest changes in optical properties • Near Nadir ≤10° • Near Edge of Scan ≥50° Cloud Top Pressure (hPa) 200 375 550 775 900 0 0.2 0.4 0.6 0.8 1 Cloud Effective Radius Ice (μm) Cloud Effective Radius Liquid (μm) Cloud Optical Depth Ice 5 10 15 20 25 5 10 15 20 25 15 20 25 30 35 15 20 25 30 35 Cloud Optical Depth Liquid

  9. L3 Statistical Uncertainty Study: Zonal Retrieval Statistics vs. VZAEffective Radius, water clouds

  10. L3 Statistical Uncertainty Study: Global Retrieval Statistics vs. Zenith AngleEffective Radius, water clouds, MODIS Aqua, April 2005 operational (all bins) fwd. nadir bin backward oblique bin (-53° to -65° VZA) 0 12 ≥24 forward oblique bin (53° to 65° VZA)

  11. Mean Cloud Fraction Difference (MOD35-MOD06) 0 10 20 30 40 (%) MOD06 cloud fraction is a quality assured subset of MOD35 to retrieve better cloud optical properties

  12. Mean Cloud Fraction Difference in Percent (MOD35-MOD06)/MOD35 0 30 60 (%) Differences are due to the QA stuff(clear sky restoral and cloud edges, thin clouds, and surfaces influences).

  13. CTP histogram from CTP (red) and CTPvsOD (blue) histogram Pressure Level (hPa) Cloud Fraction Difference in high and low cloud fraction

  14. Cloud Fraction Day Difference for 7 yrs (Aqua minus Terra) -30 0 30 FEB JAN MAR MAY APR JUN AUG JUL SEP NOV OCT DEC

  15. Grid Cell Size and Swath Overlap Cloud Top Pressure vs Latitude Swath overlap causes more cloud to be averaged into the middle cloud bin 50 40 30 Cloud Fraction 20 10 EQ 15 30 45 60 75 90 Latitudes Included

  16. Grid Cell Size and Swath Overlap Cloud Top Pressure Histogram High Cloud <400 hPa Mid Cloud >400 and <700 hPa Low Cloud >700 hPa

  17. Summary • Cloud fractions need to characterize the global cloud trend within ±1% • View angle dependencies are large across swath • 16% cloud fraction (>60 locally) • 30hPa for cloud top pressure (>200 hPa locally) • 2μm for effective radii (10μm locally) • 2 for optical depth (20 locally)

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