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References and Notes 1. K. E. Trenberth and T. J. Hoar, Geophys. Res. Lett. 24, 3057 (1997). 2. T. R. Knutson, S. Manabe, D. Gu, J. Clim. 10, 138 (1997). 3. L. Goddard and N. E. Graham, J. Geophys. Res. 102, 10423 (1997). 4. B. Wang and Y. Wang, J. Clim. 9, 1586 (1996). 5. J. Cole and E. Cook, Geophys. Res. Lett. 25, 4529, (1998). 6. M. E. Mann, R. S.(More)
Some of the global warming from anthropogenic greenhouse gases is offset by increased reflection of solar radiation by clouds with smaller droplets that form in air polluted with aerosol particles that serve as cloud condensation nuclei. The resulting cooling tendency, termed the indirect aerosol forcing, is thought to be comparable in magnitude to the(More)
Recent measurements of the single-scattering albedo omega(0) of tropospheric aerosols indicate the presence of a strongly absorbing material which has tentatively been identified as graphitic carbon (soot). Theoretical calculations, based on several different models of the way in which soot might be mixed with other aerosol materials, show that a minimum of(More)
When the production of cloud condensation nuclei in the stratocumulus-topped marine boundary layer is low enough, droplet collisions can reduce concentrations of cloud droplet numbers to extremely low values. At low droplet concentrations a cloud layer can become so optically thin that cloud-top radiative cooling cannot drive vertical mixing. Under these(More)
We show that the escape of hydrogen from early Earth's atmosphere likely occurred at rates slower by two orders of magnitude than previously thought. The balance between slow hydrogen escape and volcanic outgassing could have maintained a hydrogen mixing ratio of more than 30%. The production of prebiotic organic compounds in such an atmosphere would have(More)
The martian valley networks formed near the end of the period of heavy bombardment of the inner solar system, about 3.5 billion years ago. The largest impacts produced global blankets of very hot ejecta, ranging in thickness from meters to hundreds of meters. Our simulations indicated that the ejecta warmed the surface, keeping it above the freezing point(More)
Efficient, numerically stable, methods for the calculation of light-scattering intensity functions for concentrically coated spheres are discussed. Earlier forms of these equations are subject to various numerical difficulties which give rise to significant errors, especially for thin absorbing shells. The present equations are accurate for all refractive(More)
Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn's moon, Titan. One of Titan's most captivating features is the thick organic haze layer surrounding the moon, believed to be formed from photochemistry high in the CH(4)/N(2) atmosphere. It has been suggested that a similar haze layer may have formed on the(More)
Homogeneous freezing of nitric acid hydrate particles can produce a polar freezing belt in either hemisphere that can cause denitrification. Computed denitrification profiles for one Antarctic and two Arctic cold winters are presented. The vertical range over which denitrification occurs is normally quite deep in the Antarctic but limited in the Arctic. A 4(More)