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R. D. Cess
and
V. Ramanathan

Abstract

Cloud amount, as a climate feedback mechanism, encompasses separate and competing albedo and infrared feedbacks. In the present note we illustrate that the relative role of the infrared feedback mechanism cannot be determined from a model calculation, unless the model has the capability of predicting how the amounts of individual cloud layers change in relation to a change in total cloud cover.

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M. S. Lian
and
R. D. Cess

Abstract

Disagreement exists, with regard to different types of climate models, concerning the influence of ice-albedo feedback upon the stability of the present global climate. In view of this we have reexamined the empirical relationship between zonal albedo and temperature for use in zonally averaged energy-balance climate models, and conclude that ice-albedo feedback constitutes a relatively mild climate feedback mechanism, amplifying global climate sensitivity by roughly 25%.

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J. S. Hogan
,
R. D. Cess
,
T. Encrenaz
, and
D. Gautier

Abstract

Using recently calculated models of the Jovian atmosphere, we have derived a value of 5.0 for the H2/He mixing ratio from the Pioneer 10 infrared radiometer data. We have also computed a far-infrared spectrum corresponding to the thermal profile obtained in the Pioneer S-band occultation experiment. Our computed spectrum strongly suggests a misinterpretation of the data obtained in that experiment.

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R. D. Cess
,
B. P. Briegleb
, and
M. S. Lian

Abstract

At low latitudes the seasonal variation in the radiation budget of the earth-atmosphere system is due largely to seasonal variability in cloudiness. Making use of this, we have estimated, from three different sets of satellite data, the relative albedo versus infrared modifications associated with cloudiness variability at low latitudes. Employing satellite data sets due to Ellis and Vonder Haar (1976) and Campbell and Vonder Haar (1980), we find that the albedo modification is somewhat less than that of the infrared. But when use is made of radiation budget data derived from NOAA–NESS scanning radiometer measurements, the albedo modification dominates over that of the infrared by nearly a factor of 2. This obviously suggests that estimates of climate feedback associated with changes in cloudiness are highly dependent on the satellite data set which is employed. It is further suggested that these differences might be in part attributable to the NOAA–NESS data being derived from narrow spectral measurements.

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M. H. Zhang
,
R. D. Cess
, and
S. C. Xie

Abstract

Satellite measurements from January 1985 to December 1989 show that warmer tropical oceans as a whole are associated with less longwave greenhouse effect of clouds and less cloud reflection of solar radiation to the space. The regression slopes of longwave and shortwave cloud radiative forcings against sea surface temperatures averaged from 30°N to 30°S are about −3 and 2 W m−2 K−1, respectively. Relationships of cloud forcings and sea surface temperatures are analyzed for regions with different sizes. As has been reported in previous studies, the magnitude of area-averaged cloud radiative forcing for both longwave and shortwave radiations increases with sea surface temperatures in the equatorial eastern Pacific and is insensitive to sea surface temperatures over the tropical Pacific basin. Yet, when the region extends beyond the tropical Pacific, the magnitude decreases with sea surface temperatures. This phenomenon is shown to relate to changes in clouds over the tropical Indian Ocean and Atlantic, where sea surface temperatures increased but clouds decreased during the 1987 El Niño event. Relevance of the results to other climate changes is discussed.

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G. L. Potter
,
R. D. Cess
,
P. Minnis
,
E. F. Harrison
, and
V. Ramanathan

Abstract

This study addresses two aspects of the planetary albedo's diurnal cycle, the first of which refers to directional models of the planetary albodo. It is found that even for clear regions there appear to be deficiencies in our knowledge of how to model this quantity. Over land surfaces, for example, Nimbus-7 data for the directional planetary albedo compare best with model calculations for which a Lambertian surface is assumed, despite ample evidence that the albedo of land surfaces is dependent upon solar zenith angle. Similarly, over ocean surfaces both GOES and Nimbus-7 data produce a weaker dependence of the planetary albedo upon solar zenith angle than would be suggested by model calculations.

The second aspect of the study concerns a comparison of the diurnal amplitude factor, defined as the ratio of the diurnally averaged planetary albedo to that at noon, between two general circulation models (GCMs) and measurements made from a geostationary satellite (GOES). While these comparisons indicate reasonable consistency between the GCMs and the satellite measurements, this is due in part to compensating differences, such as an underestimate in cloud amount by a GCM being compensated for by a corresponding underestimate of the diurnal amplitude factor for overcast regions. The comparisons further underscore difficulties associated with converting local-time albedo measurements, as made from sun-synchronous satellites, to diurnally averaged albedos.

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J. T. Kiehl
,
J. J. Hack
,
M. H. Zhang
, and
R. D. Cess

Abstract

Recent studies by Cess et al. and Ramanathan et al. find that clouds absorb significantly more shortwave radiation than currently modeled by general circulation models. Initial calculations for the global annual shortwave energy budget imply that including the additional shortwave cloud absorption leads to an additional 22 W m−2 absorption in the atmosphere, with an equivalent reduction of shortwave flux at the surface. The present study investigates the climate implications of enhanced cloud absorption with the use of the National Center for Atmospheric Research Community Climate Model. The GCM response to this forcing is to warm the upper troposphere by as much as 4 K. The additional shortwave heating in the upper troposphere reduces the strength of the Hadley circulation by 12% and leads to lower surface wind speeds in the Tropics. In turn, these lower wind speeds lead to a 25 W m−2 reduction in surface latent heat flux.

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