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Stephanie P. Browner, William L. Woodley, and Cecilia G. Griffith


An analysis of 16 days from eight Atlantic storms, two in 1974 and six in 1975, objectively quantified a suspected diurnal oscillation of tropical storm cirrus cloud cover. The oscillation shows a maximum area at approximately 1700 local mean solar time and a minimum area at 0300 local mean solar time. The average ratio of the maximum area to the minimum area is 1.65.

SMS infrared imagery was analyzed with a scanning false-color densitometer to obtain area measurements of the cloudiness associated with the storms. These measurements were made approximately every 1½ h at three temperature thresholds: 253, 239 and 223 K.

Two tests were performed to rule out the possibility of the oscillation being due either to the satellite sensor or to image processing. Measurement of the ocean surface temperature, was made with SMS-I to determine whether the sensor detected a constant ocean temperature. The second test compared simultaneous area measurements obtained by SMS-I and SMS-II. The results of these tests support the storm oscillation detected.

Two other related phenomena were also observed: 1) the amplitude of the area oscillation is apparently inversely proportional to the intensity of the storm, and 2) a time-dependent, shorter period oscillation is superimposed on the daily oscillation. Inferences of causality are made.

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Two waterspouts were observed aloft from a private aircraft recently near Lower Matecumbe Key, Florida. Color slides and zoom movies of both waterspout vortices on the sea surface and aloft were obtained. A detailed description of the equipment used and a discussion of the synoptic pattern of that day are presented. The data show some interesting details regarding the dynamics of the observed waterspout circulations. Both waterspouts traversed a similar path. A subsequent ground survey of the paths taken over the Key, together with damage reports and eyewitness accounts, indicate that the second waterspout was much more intense than the first.

The authors plan to make detailed calculations, using the zoom movies, of a radial profile of the tangential and vertical wind speeds about the second waterspout vortex. Rates of forward motion and funnel diameter at various levels below the cloud base will also be obtained. An additional, more quantitative report of this interesting encounter will be forthcoming.

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