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Richard T. Hall and R. Douglas Rawcliffe

Abstract

A series of experimental measurements of the visible light angular transmittance profiles of clouds is described. The results for single-layer overcast clouds were found to correlate well with standard hemispheric and narrow-angle pyrheliometric transmittances. The resulting expression for the angular transmittance profile of an overcast cloud layer is

              T(θ) = A+B sin2θ,

where

           A = −0.0056+0.89T n , and B = −0.028+1.09T w,

and T is the transmittance measured for a field of view at the detector subtending a half angle θ centered about the sun or other light source, Tn the transmittance measured with a narrow-angle pyrheliometer, and Tw the transmittance measured with a hemispheric pyrheliometer.

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David M. Tratt, John A. Hackwell, Bonnie L. Valant-Spaight, Richard L. Walterscheid, Lynette J. Gelinas, James H. Hecht, Charles M. Swenson, Caleb P. Lampen, M. Joan Alexander, Lars Hoffmann, David S. Nolan, Steven D. Miller, Jeffrey L. Hall, Robert Atlas, Frank D. Marks Jr., and Philip T. Partain

Abstract

The prediction of tropical cyclone rapid intensification is one of the most pressing unsolved problems in hurricane forecasting. The signatures of gravity waves launched by strong convective updrafts are often clearly seen in airglow and carbon dioxide thermal emission spectra under favorable atmospheric conditions. By continuously monitoring the Atlantic hurricane belt from the main development region to the vulnerable sections of the continental United States at high cadence, it will be possible to investigate the utility of storm-induced gravity wave observations for the diagnosis of impending storm intensification. Such a capability would also enable significant improvements in our ability to characterize the 3D transient behavior of upper-atmospheric gravity waves and point the way to future observing strategies that could mitigate the risk to human life caused by severe storms. This paper describes a new mission concept involving a midinfrared imager hosted aboard a geostationary satellite positioned at approximately 80°W longitude. The sensor’s 3-km pixel size ensures that the gravity wave horizontal structure is adequately resolved, while a 30-s refresh rate enables improved definition of the dynamic intensification process. In this way the transient development of gravity wave perturbations caused by both convective and cyclonic storms may be discerned in near–real time.

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