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Status of MOD06CT: Cloud Top Properties What’s new, what’s old, what’s fixed, and what’s broken

Status of MOD06CT: Cloud Top Properties What’s new, what’s old, what’s fixed, and what’s broken Mar 2003 Richard A. Frey, H. Zhang, S. Ackerman, D. Wylie, and W. P. Menzel. Status of MOD06CT: Cloud Top Properties The algorithm and the instruments Adjusting the NEDR SFOV vs 5x5 results

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Status of MOD06CT: Cloud Top Properties What’s new, what’s old, what’s fixed, and what’s broken

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  1. Status of MOD06CT: Cloud Top Properties What’s new, what’s old, what’s fixed, and what’s broken Mar 2003 Richard A. Frey, H. Zhang, S. Ackerman, D. Wylie, and W. P. Menzel

  2. Status of MOD06CT: Cloud Top Properties The algorithm and the instruments Adjusting the NEDR SFOV vs 5x5 results Aqua vs Terra for 1 day Day vs night Terra for 1 year MODIS vs HIRS MODIS and GOES Status for collection 4

  3. Cloud Properties RTE for cloudy conditions indicates dependence of cloud forcing (observed minus clear sky radiance) on cloud amount () and cloud top pressure (pc) pc (I - Iclr) =  dB . ps Higher colder cloud or greater cloud amount produces greater cloud forcing; dense low cloud can be confused for high thin cloud. Two unknowns require two equations. pc can be inferred from radiance measurements in two spectral bands where cloud emissivity is nearly the same.  is derived from the infrared window, once pc is known.

  4. Determining Cloud Presence and Properties with MODIS Use MODIS Cloud Mask to determine cloud presence Calculate Iclr from GDAS Attempt CO2 slicing estimate of pc on 5x5 FOV average when (I - Iclr) > 5mW/m2/ster/cm-1 Estimate IRW using IRW radiances If no bands qualify, use IR window estimate for opaque cld

  5. Different ratios reveal cloud properties at different levels hi - 14.2/13.9 mid - 13.9/13.6 low - 13.6/13.3 Meas Calc pc (I1-I1clr) 11 dB1 ps ----------- = ---------------- pc (I2-I2clr) 22 dB2 ps MODIS bands 30-36

  6. Terra (left) and Aqua (right) MODIS IR NEdTs

  7. Terra Band 34 Noisy Detectors

  8. Detector to detector calibration Band 33; 13.4um Band 34; 13.7um Band 36; 14.2um Band 35; 13.9um Terra

  9. High Clouds detected by 5 km Aqua CO2 slicing with different NEDRs

  10. High Clouds (Red)NEDR: 2.5, 5, 5, 5, 0.5 for MODIS CTP 21:30 UTC on Aug. 24, 2002

  11. High Clouds (Red)NEDR: 5, 5, 5, 5, 0.5 for MODIS CTP 21:30 UTC on Aug. 24, 2002

  12. High Clouds (Red)NEDR: 7, 7, 7, 7, 0.5 for MODIS CTP 21:30 UTC on Aug. 24, 2002

  13. Low Clouds detected by 5 km Aqua CO2 slicing with different NEDRs

  14. Low Clouds (Blue)NEDR: 2.5, 5, 5, 5, 0.5 for MODIS CTP 21:30 UTC on Aug. 24, 2002

  15. Low Clouds (Blue)NEDR: 5, 5, 5, 5, 0.5 for MODIS CTP 21:30 UTC on Aug. 24, 2002

  16. Low Clouds (Blue)NEDR: 7, 7, 7, 7, 0.5 for MODIS CTP 21:30 UTC on Aug. 24, 2002

  17. High Clouds detected by 5 km Aqua CO2 slicing with different NEDRs

  18. Low Clouds detected by 5 km Aqua CO2 slicing with different NEDRs

  19. SFOV Cloud Top Pressure - Detector 5 Operational NEDR: 7, 7, 7, 7, 0.5 All Clouds (%) Thin(%) Thick(%) Opaque(%) High 18.02 5.21 8.99 3.82 Middle 19.80 0.61 6.45 12.75 Low 29.32 0.00 0.00 29.32 Clear 32.86 NEDR: 2, 2, 2, 2, 0.5 All Clouds (%) Thin(%) Thick(%) Opaque(%) High 23.84 11.33 8.57 3.94 Middle 30.44 10.65 17.552.24 Low 12.87 0.00 0.00 12.87 Clear 32.86 NEDR: 1.5, 1, 1, 1, 0.5 All Clouds (%) Thin(%) Thick(%) Opaque(%) High 22.47 10.08 8.41 3.98 Middle 33.61 12.50 19.19 1.92 Low 11.06 0.00 0.00 11.06 Clear 32.86

  20. SFOV Cloud Top Pressure from IRW vs CO2 Operational NEDR: 7, 7, 7, 7, 0.5 14.2/13.9 13.9/13.6 13.9/13.3 13.6/13.3 13.3/11 IR window CO2 High 2.75 12.17 1.71 9.30 0.80 0.12 26.72 Middle 0.00 3.01 0.47 8.39 0.15 17.47 12.03 Low 0.00 0.00 0.00 0.00 0.00 43.66 0.00 Total 61.25 38.75 NEDR: 2, 2, 2, 2, 0.5 14.2/13.9 13.9/13.6 13.9/13.3 13.6/13.3 13.3/11 IR window CO2 High 9.53 12.88 1.92 10.42 0.64 0.12 35.39 Middle 0.78 21.69 3.28 18.46 0.14 0.98 44.35 Low 0.00 0.02 0.00 0.01 0.00 19.13 0.03 Total 20.22 79.78 NEDR: 1.5, 1, 1, 1, 0.5 14.2/13.9 13.9/13.6 13.9/13.3 13.6/13.3 13.3/11 IR window CO2 High 11.11 12.67 2.02 6.92 0.63 0.11 33.35 Middle 1.54 28.45 4.93 14.63 0.14 0.38 49.68 Low 0.00 0.04 0.00 0.01 0.00 16.43 0.05 Total 16.92 83.08

  21. AQUA MODIS 630UTC 24Aug02 vis(left) and IRW (right)

  22. AQUA/MODIS SFOV High Clouds(yellow) on 06:30UTC Aug. 24, 2002NEDR:7 7 7 7 0.5

  23. AQUA/MODIS SFOV High Clouds(yellow) on 06:30UTC Aug. 24, 2002NEDR:1.5 1 1 1 0.5

  24. AQUA/MODIS SFOV Middle Clouds(Red) on 06:30UTC Aug. 24, 2002NEDR:7 7 7 7 0.5

  25. AQUA/MODIS SFOV Middle Clouds(Red) on 06:30UTC Aug. 24, 2002NEDR:1.5 1 1 1 0.5

  26. AQUA SFOV CTP 630UTC 24 Aug 02 Yellow: CO2 Red: IRW IRW Small NEDR Big NEDR

  27. AQUA/MODIS SFOV CTPon 06:30UTC Aug. 24, 2002Yellow: CO2 Red: IRWNEDR:7 7 7 7 0.5

  28. AQUA/MODIS SFOV CTPon 06:30UTC Aug. 24, 2002Yellow: CO2 Red: IRW NEDR:1.5 1 1 1 0.5

  29. 5 km Aqua Cloud Stats for 24 Aug 02 with NEDR ( 7, 7, 7, 7, 0.5) (Aqua NEDR – Terra NEDR is less than 2% for all entries) 20-60 North Latitude All Clouds (%) Thin(%) Thick(%) Opaque(%) High 20.28 (+0.29) 6.64 (+0.24) 10.53 (+0.01) 3.12 (+0.04) Middle 13.67 (-0.08) 0.35 (+0.15) 3.38 (+1.30) 9.95 (-1.52) Low 27.12 (-0.21) 0.00 (0.00) 0.00 (0.00) 27.12 (-0.21) Clear 38.92 (-0.01) 20 S-20N Tropics All Clouds (%) Thin(%) Thick(%) Opaque(%) High 26.33 (-0.64) 9.11 (-0.75) 12.83 (+0.10) 4.38 ( 0.0) Middle 12.39 (+0.32) 0.44 (-0.13) 3.12 (+0.72) 8.83 (-0.27) Low 32.15 (+0.33) 0.00 (0.00) 0.00 (0.00) 32.15 (+0.33) Clear 29.14 (0.00) 20-60 South Latitude All Clouds (%) Thin(%) Thick(%) Opaque(%) High 20.44 (-0.41) 5.13 (+0.36) 10.99 (-0.9) 4.32 (+0.13) Middle 18.76 (+0.99) 0.62 (+0.27) 6.71 (+2.24) 11.43 (-1.52) Low 31.99 (-0.57) 0.00 (0.00) 0.00 (0.00) 31.99 (-0.57) Clear 28.82 (0.00) Global statistics All Clouds (%) Thin(%) Thick(%) Opaque(%) High 20.11 (+0.25) 6.03 (-0.44) 9.42 (-0.24) 4.67 (+0.07) Middle 22.82 (-0.10) 0.54 (+0.18) 5.76 (+1.64) 16.53 (-1.91) Low 27.64 (-0.15) 0.00 (0.00) 0.00 (0.00) 27.64 (-0.15) Clear 29.42 (-0.01)

  30. Aqua Global mean CTP distribution on 24 Aug 02

  31. Seasonal Percentage High Clouds from Terra MODIS Top - Boreal Spring (Mar. 2001 - May. 2001) Bottom - Boreal Summer (Jun. 2001 - Aug. 2001)

  32. Seasonal Percentage High Clouds from Terra MODIS Top - Boreal Autumn (Sep. 2001 - Nov. 2001) Bottom - Boreal Winter (Dec. 2001 - Feb. 2002)

  33. Annual Percentage High Clouds from Terra MODIS January - December 2001 High clouds defined as < 400 mb Months equally weighted (mean of 12 monthly percentages)

  34. ISCCP (top), HIRS (mid), & MODIS (bot) for Jul (left) & Dec (right)

  35. Conclusions from HIRS CO2 Observations of Tropical (20N-20S) Cloud Cover over Ocean * All cloud cover is very stable * Clouds are detected in 75% of HIRS observations * N15 is out of family (HIRS 3) starting 1998

  36. HIRS Tropical Clouds 80% 30% MODIS Tropical Clouds • Conclusions from MODIS Comparisons • MODIS shows similar annual trends in high clouds • * MODIS finds fewer high clouds but more total clouds

  37. 5x5 Aqua 1 day vs HIRS Global High Clouds

  38. 20 km HIRS (blue) and 5 km Aqua MODIS results (black) for 24 Aug 02

  39. Aqua 5 km Clouds 24 Aug 02 For LAND surface only 20-60 North Latitude Descending Orbits ( Day time). All Clouds (%) Thin(%) Thick(%) Opaque(%) High 21.03 6.34 10.48 4.21 Middle 12.70 0.78 4.45 7.48 Low 23.92 0.00 0.00 23.92 Clear 42.55 20-60 North Latitude Ascending Orbits ( Night time ) All Clouds (%) Thin(%) Thick(%) Opaque(%) High 22.58 8.05 11.18 3.36 Middle 13.73 0.14 2.89 10.69 Low 14.96 0.00 0.00 14.96 Clear 48.73

  40. Aqua 20 km Clouds 24 Aug 02 For LAND surface only 20-60 North Latitude Descending Orbits ( Day time). All Clouds (%) Thin(%) Thick(%) Opaque(%) High 23.04 8.75 11.54 2.74 Middle 11.36 0.74 3.54 7.09 Low 26.34 0.00 0.00 26.34 Clear 39.26 20-60 North Latitude Ascending Orbits ( Night time). All Clouds (%) Thin(%) Thick(%) Opaque(%) High 23.19 9.10 11.34 2.75 Middle 14.11 0.15 2.66 11.31 Low 17.41 0.00 0.00 17.41 Clear 45.28

  41. Aqua 5 km Clouds 24 Aug 02 For WATER surface only 20-60 North Latitude Descending Orbits ( Day time). All Clouds (%) Thin(%) Thick(%) Opaque(%) High 19.35 6.01 10.56 2.78 Middle 12.09 0.28 3.17 8.64 Low 38.16 0.00 0.00 38.16 Clear 30.40 20-60 North Latitude Ascending Orbits ( Night time). All Clouds (%) Thin(%) Thick(%) Opaque(%) High 19.18 5.86 10.43 2.90 Middle 16.65 0.30 3.44 12.91 Low 53.08 0.00 0.00 53.08 Clear 11.09

  42. Aqua 20 km Clouds 24 Aug 02 For WATER surface only 20-60 North Latitude Descending Orbits ( Day time). All Clouds (%) Thin(%) Thick(%) Opaque(%) High 20.75 7.57 11.02 2.16 Middle 11.48 0.31 2.90 8.27 Low 43.73 0.00 0.00 43.73 Clear 24.04 20-60 North Latitude Ascending Orbits ( Night time). All Clouds (%) Thin(%) Thick(%) Opaque(%) High 20.11 6.80 10.91 2.40 Middle 16.46 0.26 3.36 12.84 Low 56.34 0.00 0.00 56.34 Clear 7.09

  43. Effect of emissivity adjustments very thin clouds (0~0.2) thin clouds (0.2~0.5) Some low clds moved up thick clouds (0.5~0.95) all clouds

  44. 1647 UTC 21 Jul 1946 UTC 21 Jul 0746 UTC 22 Jul 1846 UTC 22 Jul

  45. MODIS cloud top products from Terra and Aqua Hourly values of high cloud frequencies from GOES 21 Jul 22 Jul 3 2 1

  46. Changes to MOD06CT for Collection 4: 1) Modified quality check on water vapor mixing ratio values from ancillary (GDAS) profiles.  Results in many less missing values of cloud top pressure and effective emissivity. 2) Updated transmittance model. 3) Added Aqua processing capability. 4) Updated product confidence flag to facilitate proper L3 compositing. 5) Adjusted code so that atmospheric moisture is properly specified. 6) Added satellite-dependent noise (NEDRs) thresholds.

  47. Low cloud problem: 1) MOD06CT algorithm is capable of properly identifying the vast majority of low-level clouds (700-1000 mb) .  2) The ability to properly specify cloud heights in these cases is limited.  Observed 11 um brightness temperatures are compared to the nearest GDAS temperature profile.  The relatively coarse vertical (~ 50 mb) and spatial (1 deg.) resolutions of these profiles inhibits more accurate retrievals. 3) Using a local model with more resolution might help in local applications.

  48. Remaining Issues: 1) Cloud top temperature histogram classes for tropical deep convective clouds.  We need to identify clouds at least as cold as 190K. 2) Clear-sky radiance bias adjustments to forward calculations.  Full advantage of MODIS capabilities is not taken because of uncertainties between forward radiance calculations and observations.  Questions about how to properly implement a bias correction also remain.  Should corrections be made detector-by-detector or for 5x5 pixel averages?  On what spatial and temporal scales should bias statistics be collected and by which process?  An existing or new PGE? 3) Detector to detector differences must be mitigated (destriping) to get more CO2 slicing determinations of cloud properties.

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