P2.10

Comparisons of cloud analyses from independent infrared and sounder retrievals

Robert P. d'Entremont, AER, Lexington, MA; and D. P. Wylie

Comparison is made of cloud attributes, both spatial and radiative, obtained for the same cloud scenes using radiance measurements from the independent imagers and sounders onboard geostationary GOES and polar-orbiting TIROS platforms. Emphasis is placed on cirrus radiative and spatial attributes, including frequency of occurrence, optical thickness, and cloud temperature. Imager retrievals analyze multispectral thermal infrared (TIR) radiances in the 3.9, 6.7, and 10.8-um window channels while the sounder retrievals incorporate the CO₂ slicing technique in the 13-15-um carbon dioxide absorption bands. Cloud emissivity and temperature are common to both the imager and sounder retrievals, and will be compared directly.

Multiple cirrus analysis models are useful for verifying independently derived cirrus characteristics within the same cloud scene. The CO₂ technique retrieves effective emissivity Ne, the product of cloud fraction "N" and emissivity "e," and is capable of detecting thin cirrus at levels where the carbon-dioxide weighting functions peak. For each relatively coarse sounder field of view a cirrus cloud fraction estimate "N" can be made from the imager data using a multispectral cloud mask. The sounder emissivity e can then be decoupled from the effective emissivity Ne by dividing by N. This in turn allows for direct comparison between the imager and sounder emissivity retrievals for those cloudy pixels that lie within the sounder pixel.

Additionally, comparisons will be made between the summary statistics of both retrievals for a time series of data over the northeast US and adjacent Atlantic Ocean. Frequency distributions of cloud-top temperature (height, pressure) and optical thickness will be made for the sounder and TIR retrievals, and plots of emissivity versus cloud-top height will also be made in order to investigate whether there is a dependence between cloud temperature and cloud optical properties. These results will provide a valuable comparison between CO₂ Slicing, for which long-term cloud climatologies exist, and an independent but coterminous TIR imager cloud analysis.

Suggested Area of Interest: (2) Climatology and Long-term Satellite Data Studies

  Extended Abstract (136K)

Poster Session 2, Climatology and Long-term Satellite Studies
Monday, 15 October 2001, 2:15 PM-4:00 PM

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