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N. T. O'Neill, A. Royer, P. Coté, and L. J. B. McArthur

under the higher nominal water vapor absorption line can be accounted for given the uncertaintyin the computed optical depths as well as the uncertainty in the extracted water content values from the935-nm channel (Table 5 ). The distance above eitherof the absorption lines would thus be an indication ofthe variability in scattering properties of the aerosolsfor small aerosol optical depth. Table 5 gives an indication of the uncertainty in theextracted water vapor absorption optical depths. If

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R. A. Raschke and S. K. Cox

average optical depth over the fieldof view. Using this averaged or equivalent value ofoptical depth one is able to approximately reproducethe bulk radiative properties of the layer. Avaste andVaynikko (1973) confirm this first order agreement;however, they go on to point out that the transmittancefor the broken layer is invariably higher than that forthe uniform, mean value of optical depth. The five detectors were sampled at 1 min intervals,thus the 10 min average values c6nsist of ten sets

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Rasmus Lindstrot, Rene Preusker, and Jürgen Fischer

about clouds obtainable from channels in the CO 2 absorption band around 15 μ m. The so-called CO 2 -slicing technique, as applied to, for example, MODIS ( Smith and Platt 1978 ; Wielicki and Coakley 1981 ; Menzel et al. 2006 ), provides better sensitivity to semitransparent cirrus clouds and their optical properties and is thus superior to a simple 11- μ m brightness temperature–based retrieval, especially if applied in cases of cirrus overlapping water clouds (e.g., Chang and Li 2005b ). 3

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A. J. Prata and I. J. Barton

capability of providingmultiangle multichannel measurements globally.1. Introduction Clouds exert a considerable influence on climate.Depending upon their optical properties they can provide either positive or negative feedback to the climatesystem. Semitransparent high clouds can alter the radiation received at the earth's surface by reflection ofincoming solar radiation and by modifying the quantityof outgoing longwave radiation. These clouds are particularly important to climate because they have

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Michael D. King, Dale M. Byrne, John A. Reagan, and Benjamin M. Herman

year and locality. More information concerning the properties ofaerosol particles is contained in measurements ofthe wavelength dependence of the optical depth asfirst suggested by /~ngstr6m (1929). Atmospherictransmission measurements at two wavelengthshave often been collected at individual stations inorder to estimate the parameters of Angstr6m's(1929) empirical formula for the wavelength dependence of the aerosol optical thickness. Among themore recent studies of this kind are measurementsin

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Glenn E. Shaw, John A. Reagan, and Benjamin M. Herman

supplyuseful information about the aerosol size distribution.5. Wavelength dependency of aerosol optical depth and its relation to aerosol size distributions and mass loading The aerosol particle contribution to optical deptharises from the cumulative effects of scattering andabsorption by the particulates distributed throughoutthe atmosphere. Assuming horizontal homogeneity, theaerosol optical depth component r~(X) may be relatedto the extinction properties of the aerosol particles atany height h

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U. Schumann, B. Mayer, K. Graf, and H. Mannstein

, and droxtals (with 10–45- μ m effective radius) ( Baum et al. 2005a , b ). The optical properties in the solar spectral range (volume extinction coefficient, single-scattering albedo, and asymmetry factor) of the particle ensembles are taken from Key et al. (2002) , except for droxtals, which were provided by H. Gang and P. Yang (2009, personal communication). Optical properties for the thermal spectral range were taken from Yang et al. (2005) . The data for droxtals and those in the thermal

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Robert S. Stone, Graeme L. Stephens, C. M. R. Platt, and S. Banks

ambiguity of interpreting satellite radiancemeasurements when thin cirrus clouds are present. Theneed to characterize the radiative properties of cirrusclouds, especially optical depth, has been well statedin the studies of Stephens and Webster ( 1981 ) and ofPlatt ( 1981 ), among others. Current methods for retrieving cloud properties fromsatellite observations tend to fall into two broad classes:353354 JOURNAL OF APPLIED METEOROLOGY

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Nicola L. Pounder, Robin J. Hogan, Tamás Várnai, Alessandro Battaglia, and Robert F. Cahalan

. Figure 1 shows an example of a retrieval using a triangular extinction-coefficient profile with a total optical depth of 40. Triangular profiles of liquid water content are commonly observed (e.g., Slingo et al. 1982) , indicating an extinction coefficient with an approximately triangular profile as well. For this retrieval, λ = 10 5 was chosen using the method described in section 3f below. We use scattering properties that are suitable for liquid droplets: an asymmetry factor of 0.85, single

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David E. Pitts, W. E. McAllum, Michael Heidt, Keith Jeske, J. T. Lee, Dan DeMonbrun, Al Morgan, and John Potter

much highertemporal resolution, with radiosonde data for prediction of precipitable water. 3) Cirrus has the property of causing optical depthat 0.8730 t~m to be greater than at 1.04 ~m, permittingcirrus effect removal from the data set used by thepercipitable water algorithm. 4) Aerosol effects can be effectively removed frominfluencing precipitable water estimated by the ratioalgorithm. However, cirrus causes anomalously lowreadings of precipitable water if removal of the effectsis not

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