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Cloud Trends and Anomalies Observed by MISR

Cloud Trends and Anomalies Observed by MISR. R. Davies. Physics Department The University of Auckland, New Zealand. 9 view angles at Earth surface: 70.5º, 60º, 45.6º, 26.1º forward/ aftward and 0º Multiple spectral bands at each angle: MISR/Terra: 446, 558, 672, 866 nm

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Cloud Trends and Anomalies Observed by MISR

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  1. Cloud Trends and Anomalies Observed by MISR R. Davies Physics Department The University of Auckland, New Zealand GEWEX Cloud Workshop

  2. 9 view angles at Earth surface: 70.5º, 60º, 45.6º, 26.1º forward/ aftward and 0º Multiple spectral bands at each angle: MISR/Terra: 446,558,672,866 nm 400-km swath: 9-day global coverage 275 m - 1.1 km sampling 7 minutes to observe each scene at all 9 angles MISR: Multi-angle Imaging Spectro-Radiometer GEWEX Cloud Workshop

  3. MISR : observation concept 9 view angles at Earth surface: +70.5º to –70.5º stereo match to get Reflecting Layer Reference Altitude (RLRA) every 2.2 km (90% coverage) 10-day area-weighted zonal averages of mean RLRA (>100 independent samples) similarly, coverage by height independent of radiometric calibration consistent processing since 3/2000 Terra: 10:30 am sun-synchronous GEWEX Cloud Workshop

  4. first: seasonal cycles • globally averaged cloud fraction • 10-day means (≈130 independent orbits) • area weighted zonal averages • avoids overweighting of polar latitudes by Terra • stratified by height • surface (≈clear) • low (<3 km) • middle (3–7 km) • high (> 7 km) GEWEX Cloud Workshop

  5. GEWEX Cloud Workshop

  6. 0.362±0.001 i.e. global mean cloud fraction > 0.638 at 10:30 am GEWEX Cloud Workshop

  7. 0.321±0.001 GEWEX Cloud Workshop

  8. 0.1545±0.0004 GEWEX Cloud Workshop

  9. 0.161±0.001 GEWEX Cloud Workshop

  10. second: global cloud anomalies • deseasonalized 10-day anomalies • mean year anomaly with expected sampling error • linear regression GEWEX Cloud Workshop

  11. GEWEX Cloud Workshop

  12. GEWEX Cloud Workshop

  13. GEWEX Cloud Workshop

  14. GEWEX Cloud Workshop

  15. GEWEX Cloud Workshop

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  18. third: global implications • how do cloud albedos change? • what about cloud heights? GEWEX Cloud Workshop

  19. MISR : observation concept 9 view angles at Earth surface: +70.5º to –70.5º multiple spectral bands at each angle: 446,558,672,866 nm on-board calibration system: ≈1% relative accuracy ‘expansive’ albedo integrated over the view from 30 km, averaged over swath width (300 km) energy-weighted, area-weighted, 10-day zonal averages (>100 independent samples) consistent (reprocessed) data from 5/2000 (discontinuously) to present Terra: 10:30 am sun-synchronous GEWEX Cloud Workshop

  20. green band albedo GEWEX Cloud Workshop

  21. GEWEX Cloud Workshop

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  24. spectral albedo summary • all MISR bands show similar anomalies • regional anomalies are consistently larger • sampling uncertainty (1s) • 0.003 (10-day, global) • 0.0004 (12-month, global) • interannual albedo changes <0.001 (0.3%) • overall difference 2005–2000 • <0.2% • <0.3 W m-2 (equivalent broadband absorption) • well within the expected radiometric uncertainty GEWEX Cloud Workshop

  25. GEWEX Cloud Workshop

  26. GEWEX Cloud Workshop

  27. thru 8/05 global ‘trend’ –11±2 m/yr GEWEX Cloud Workshop

  28. GEWEX Cloud Workshop

  29. height and fraction summary • MISR has the ability to produce consistent records of reflecting layer reference altitude and coverage by height • interannual differences • sampling error of ±11 m in height, ±0.002 in coverage • difference of –44 ±11 m between first and last full year • consistent with a reduction in tropical high cloud (ITCZ) –70 ±12 m/yr • these differences exceed the sampling uncertainty • unlike the albedo time series, the height differences are unaffected by radiometric calibration GEWEX Cloud Workshop

  30. thru 5/06 preliminary global ‘trend’ –5±3 m/yr GEWEX Cloud Workshop

  31. wrap up: MISR 2000-2006 • can characterize the seasonal variability of cloud fraction (+height and albedo) • can limit the secular trend to less than ≈0.001/yr in global total cloud fraction • interannual variability in global total cloud fraction ≈0.001 • larger relative changes in high cloud amount, with measurable interannual changes in mean cloud top height ≈10m globally, ≈100 m in tropics • effective height change > albedo change (radiative forcing) GEWEX Cloud Workshop

  32. Distance between a features seen with 2 cameras: • ∆D (Xc,Yc) CTH (Xg,Yg) D Cloud reconstruction Obtaining cloud top height and cloud position 2) Cloud top height calculation: CTH = ∆D / [tan (2 -1)] 3) Parallax correction : Xc = Xg + CTH * tan() * sin (  ) Yc = Yg + CTH * tan() * cos (  ) GEWEX Cloud Workshop

  33. GEWEX Cloud Workshop

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