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Seasonal and Inter-annual Variations of Polar Cloud Cover

Seasonal and Inter-annual Variations of Polar Cloud Cover. Seiji Kato 1 , Norman G. Loeb 2 , Patrick Minnis 3 , Jennifer A. Francis 4 , Thomas P. Charlock 3 , David A. Rutan 5 , Eugene E. Clothiaux 6 , Szedung Sun-Mack 5 , and Fred Rose 5

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Seasonal and Inter-annual Variations of Polar Cloud Cover

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  1. Seasonal and Inter-annual Variations of Polar Cloud Cover Seiji Kato1, Norman G. Loeb2, Patrick Minnis3, Jennifer A. Francis4, Thomas P. Charlock3, David A. Rutan5, Eugene E. Clothiaux6, Szedung Sun-Mack5, and Fred Rose5 1 Hampton University, 2 National Institute of Aeronautics 3 NASA Langley Research Center, 4 Rutgers University, 5 Analytical Service & Materials, Inc, 6 the Pennsylvania State University GEWEX Cloud Assessment July 7-8, 2006 Madison, Wisconsin

  2. Outline • Comparison of cloud fraction over the Arctic (60N-90N)and Antarctic (60S-90S). • Comparison with ground-based data. • Consistency check of cloud detection using CERES multi-angle observations. • Cloud and radiation trend over the Arctic.

  3. Data • Terra SSF Ed2B_Rev1 from March 2000 through Feb. 2004 and Aqua Ed1B from Aug.2002 through Feb. 2004. • TOVS cloud retrieval from J. Francis • MODIS collection4. • ISCCP (D2). • Area-weighted mean values over the Arctic (60-90N) and over the Antarctic (60-90S).

  4. Seasonal Variations, Cloud Cover Arctic Antarctic Snow/Sea ice Snow/Sea ice

  5. Seasonal variation Clouds over Ocean and Land Day + Night CERES ed2B and MODIS collection 4

  6. Antarctic Retrieved from MODIS radiances by the CERES cloud algorithm

  7. Summary: Seasonal Cloud Variation • The cloud fraction from MODIS over the Arctic changes from 0.8 In summer to 0.5 In winter. • The cloud fraction over land and ocean in the Arctic show a similar seasonal variation. • The cloud fraction over the Antarctic does not show much seasonal variations. • A larger difference in the winter cloud fraction than the summer cloud fraction (less than 10%).

  8. Comparison with Cloud Occurrence Derived from Ground-based Active Sensors Day + Night clouds over Barrow, AK March 2000 – Feb. 2004 CERES: CERES cloud algorithm Radar: Millimeter Cloud Radar Lasers: micro-pulse lidar Vaisala celometer

  9. Large differences in Radar and Laser-based Cloud Occurrence

  10. Smaller Difference in Cloud Occurrence Clear day

  11. Cloud Vertical Profile Daytime Barrow, AK

  12. Cloud Vertical Profile, Nighttime

  13. Seasonal Cloud Cover over Barrow, AK(March 2000 – Feb. 2004)

  14. Comparison with LW anomaly Barrow CERES Correlation coefficient = 0.57 NyAlesund (Norway) CERES Correlation coefficient = 0.40 Solid circle: Cloud Open square: Downward longwave

  15. Nighttime Cloud Cover over Antarctica

  16. Terra-Aqua CERES Cloud Algorithm Difference Aqua detection has more Colder clear-sky scenes

  17. CERES-MODIS collocation MODIS pixels CERES footprint Clear scenes can be viewed from different angles by CERES

  18. Nighttime Longwave over Antarctica

  19. Daytime Trends Over the Arctic 2.0±2.0 W m-2 0.047±0.041 (0.016 Summer 0.033 Spring by Wang and Key, J. Climate, 2005) -0.064±0.055 At a 80% confidence level

  20. Cloud trend over Barrow derived from lidars From March 2000 through Feb. 2004

  21. Cloud trend between March 2000-Feb. 2004 Day Day +Night

  22. Summary • The cloud fraction over the Arctic changes from 0.8 in summer to 0.5 in winter. • The cloud fractions over land and ocean in the Arctic show a similar seasonal variation. • The cloud fraction over the Antarctic does not show a large seasonal variation. • A larger difference in the winter cloud fraction than the summer cloud fraction (less than 10%). • The range of optical thickness has to defined for polar cloud fraction comparison. • The daytime cloud fraction over the Arctic from March 2000 through February 2004 increased at a rate of 0.047 decade. • The corresponding top-of-atmosphere (TOA) shortwave irradiances decreases at a rate of –2W m^-2, but the trend is less statistically significant. • The cloud fraction and TOA shortwave irradiance over the Antarctic show no significant trend during the same period.

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