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- Author or Editor: S. Twomey x
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Abstract
Using Nuclepore filters at a sequence of flow rates, to discriminate according to particle size, and a suitable mathematical inversion procedure, particle size distributions have been obtained for surface atmospheric aerosol samples. Measurements in relatively unpolluted air at Robertson, N.S.W., Australia, yield a fairly reproducible size distribution, with a maximum always close to 10−6 cm radius; measurements in more polluted air at The University of Arizona have led to very similar size distributions.
Abstract
Using Nuclepore filters at a sequence of flow rates, to discriminate according to particle size, and a suitable mathematical inversion procedure, particle size distributions have been obtained for surface atmospheric aerosol samples. Measurements in relatively unpolluted air at Robertson, N.S.W., Australia, yield a fairly reproducible size distribution, with a maximum always close to 10−6 cm radius; measurements in more polluted air at The University of Arizona have led to very similar size distributions.
Abstract
Using published data for water vapor absorption and for absorption by liquid (or ice) water, the absorption of solar radiation by clouds was computed for several representative cloud models. Absorption was found to approach 20% of the solar flux for the more absorbing and thicker clouds. There were systematic differences between continental and maritime clouds, the latter absorbing more for the same cloud thickness—an effect produced by the greater absorption efficiency of the larger maritime drops.
Abstract
Using published data for water vapor absorption and for absorption by liquid (or ice) water, the absorption of solar radiation by clouds was computed for several representative cloud models. Absorption was found to approach 20% of the solar flux for the more absorbing and thicker clouds. There were systematic differences between continental and maritime clouds, the latter absorbing more for the same cloud thickness—an effect produced by the greater absorption efficiency of the larger maritime drops.
Abstract
The difficulties and instabilities accompanying the inversion of radiance data to infer temperature structure are closely related to the high degree of interdependence existing among these nominally independent measurements.
The radiance measurements discussed in the accompanying papers are shown to be interdependent to a marked degree. It is shown that one of the measurements can be predicted from the others with an accuracy which is only a little worse than the experimental accuracy.
The application of this kind of analysis to determine optimum choices of measurements and the information content thereof is outlined.
Abstract
The difficulties and instabilities accompanying the inversion of radiance data to infer temperature structure are closely related to the high degree of interdependence existing among these nominally independent measurements.
The radiance measurements discussed in the accompanying papers are shown to be interdependent to a marked degree. It is shown that one of the measurements can be predicted from the others with an accuracy which is only a little worse than the experimental accuracy.
The application of this kind of analysis to determine optimum choices of measurements and the information content thereof is outlined.
Abstract
Combustion Processes that Produce greenhouse gases also increase cloud condensation nuclei (CCN) concentrations, which in turn increase cloud droplet concentrations and thereby cloud albedo. A calculation of cloud susceptibility, defined in this work as the increase in albedo resulting from the addition of one cloud droplet per cubic centimeter (as cloud liquid water content remains constant), is made through the satellite remote sensing of cloud droplet radius and optical thickness. The remote technique uses spectral channels of the Advanced Very High Resolution Radiometer (AVHRR) instrument on board NOAA polar-orbiting satellites. Radiative transfer calculations of reflectance and effective surface and cloud emissivities are made for applicable sun and satellite viewing angles, including azimuth, at various radii and optical thickness for each AVHRR channel. Emission in channel 3 (at 3.75 µm) is removed to give the reflected solar component. These calculations are used to infer the radius and optical thickness that best match the satellite measurements. An approximation for the effect of the atmosphere on the signal received by the AVHRR is included in the analysis. Marine stratus clouds. as well as being important modifiers of climate, are cleaner than continental clouds and so likely to be of higher susceptibility. Analysis of several stratus scenes, including some containing ship tracks supports this expectation. The retrieved range of susceptibilities for all marine stratus clouds studied varied by about two orders of magnitude. This variation implies that climate studies that include possible marine stratus albedo modification from anthropogenic CCN are incomplete without accounting for existing susceptibilities.
Abstract
Combustion Processes that Produce greenhouse gases also increase cloud condensation nuclei (CCN) concentrations, which in turn increase cloud droplet concentrations and thereby cloud albedo. A calculation of cloud susceptibility, defined in this work as the increase in albedo resulting from the addition of one cloud droplet per cubic centimeter (as cloud liquid water content remains constant), is made through the satellite remote sensing of cloud droplet radius and optical thickness. The remote technique uses spectral channels of the Advanced Very High Resolution Radiometer (AVHRR) instrument on board NOAA polar-orbiting satellites. Radiative transfer calculations of reflectance and effective surface and cloud emissivities are made for applicable sun and satellite viewing angles, including azimuth, at various radii and optical thickness for each AVHRR channel. Emission in channel 3 (at 3.75 µm) is removed to give the reflected solar component. These calculations are used to infer the radius and optical thickness that best match the satellite measurements. An approximation for the effect of the atmosphere on the signal received by the AVHRR is included in the analysis. Marine stratus clouds. as well as being important modifiers of climate, are cleaner than continental clouds and so likely to be of higher susceptibility. Analysis of several stratus scenes, including some containing ship tracks supports this expectation. The retrieved range of susceptibilities for all marine stratus clouds studied varied by about two orders of magnitude. This variation implies that climate studies that include possible marine stratus albedo modification from anthropogenic CCN are incomplete without accounting for existing susceptibilities.
Abstract
Using actual rainfall records for selected areas, one can by computer simulation apply hypothetical seeding effects and then compare the results obtained and inferences drawn by individual “experimenters” who have superimposed the effects of seeding on the natural variations of rainfall in space and in time. In this way it is possible to infer which kinds of experimental design are preferable and the duration of experiment likely to give meaningful results in a given area for some prescribed increase by seeding. Some results for three different Australian areas are given. These show a marked superiority of the crossover design as compared with target-control or single-area experiments. They also suggest that in more favorable areas a meaningful result could be obtained with a four- to eight-year experiment when the average increase due to seeding was 10%, but in the less favorable (arid) areas even a 16-year experiment would not be long enough. An average 20% increase would, however, be detectable with confidence even in the least favorable area but it would require an experimental period of about 16 years.
Abstract
Using actual rainfall records for selected areas, one can by computer simulation apply hypothetical seeding effects and then compare the results obtained and inferences drawn by individual “experimenters” who have superimposed the effects of seeding on the natural variations of rainfall in space and in time. In this way it is possible to infer which kinds of experimental design are preferable and the duration of experiment likely to give meaningful results in a given area for some prescribed increase by seeding. Some results for three different Australian areas are given. These show a marked superiority of the crossover design as compared with target-control or single-area experiments. They also suggest that in more favorable areas a meaningful result could be obtained with a four- to eight-year experiment when the average increase due to seeding was 10%, but in the less favorable (arid) areas even a 16-year experiment would not be long enough. An average 20% increase would, however, be detectable with confidence even in the least favorable area but it would require an experimental period of about 16 years.
Abstract
Samplings Of cloud droplets were compared with airborne cloud nuclei measurements in air below cloud base. The number concentration of the cloud droplets agreed closely with the number obtained from the nuclei measurements.
Abstract
Samplings Of cloud droplets were compared with airborne cloud nuclei measurements in air below cloud base. The number concentration of the cloud droplets agreed closely with the number obtained from the nuclei measurements.
Abstract
The smoke from sugar cane fires was found to be a prolific source of cloud nuclei and to increase very greatly the number concentration of droplets in clouds formed well downwind from the fires.
Abstract
The smoke from sugar cane fires was found to be a prolific source of cloud nuclei and to increase very greatly the number concentration of droplets in clouds formed well downwind from the fires.
Abstract
The mean concentration of cloud nuclei over Colorado is found to he about three times that over the Caribbean up to SWO feet above the surface. The contrast decreases upwards and at 17,000 feet there is no appreciable difference.
Abstract
The mean concentration of cloud nuclei over Colorado is found to he about three times that over the Caribbean up to SWO feet above the surface. The contrast decreases upwards and at 17,000 feet there is no appreciable difference.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
Airborne measurements at flight level of cloud nuclei have been carried out during approximately 100,000mi of flight over wide areas of the world. A thermal diffusion chamber was used to obtain cloud-nucleispectra which present the concentration of active nuclei as a function of supersaturation over the rangeof supersaturation of interest in cloud formation. The results confirm previous conclusions that continentalair masses are systematically richer in cloud nuclei and indicate that the median of cloud nuclei over theopen ocean is reasonably predictable and varied little from region to region. Over continents the medianspectrum does not seem to vary greatly even when North America was compared to Africa and Australia;however, the variability about the median is much greater over land when compared to ocean areas. Theresults indicate that the lifetime of cloud nuclei, at least over the oceans, is about 3 days. The results requirea widespread and relatively uniform source of cloud nuclei both over the oceans and over the land, and itis indicated that the sources of nuclei are not largely dependent on industrial or other man-made pollution.
Abstract
Airborne measurements at flight level of cloud nuclei have been carried out during approximately 100,000mi of flight over wide areas of the world. A thermal diffusion chamber was used to obtain cloud-nucleispectra which present the concentration of active nuclei as a function of supersaturation over the rangeof supersaturation of interest in cloud formation. The results confirm previous conclusions that continentalair masses are systematically richer in cloud nuclei and indicate that the median of cloud nuclei over theopen ocean is reasonably predictable and varied little from region to region. Over continents the medianspectrum does not seem to vary greatly even when North America was compared to Africa and Australia;however, the variability about the median is much greater over land when compared to ocean areas. Theresults indicate that the lifetime of cloud nuclei, at least over the oceans, is about 3 days. The results requirea widespread and relatively uniform source of cloud nuclei both over the oceans and over the land, and itis indicated that the sources of nuclei are not largely dependent on industrial or other man-made pollution.
