131 



The integrated transport of latent and sensible heat was computed for 

 all disturbances and mean values for the whole area are presented in TJable k. 

 These mean values are compared with values which would have been obtained had 

 the whole region been covered by a uniform trade wind, maintaining an average 

 speed within the limits specified, for periods of 1 to i+ days. Climatic 

 charts for the Atlantic from 15°S to 15°N from September to November 

 (Mac Donald, 1938) show that average wind speeds are everywhere less than 

 6.7 m sec'-'-, and over most of the region less than 5 -0 m sec"-^. From Table li- 

 the average value of Q^ would be between l80 and 380 cal cm"^day~l and of 

 Qs between 5.^ and 10. 5 cal cm-2 day'l. The occurrence of a moderate synoptic 

 disturbance of dimensions similar to those considered above would greatly 

 alter the distribution of energy input within these latitudes. Only during 

 the months of November through May do average winds in excess of 7«2 m sec"-^ 

 cover a significant portion of the region 15°N to 15°S. At this time of the 

 year within the moderate to strong trade wind regions, the latent heat flux 

 would approach that associated with moderate to strong disturbances. For 

 the remainder of the year. I.e., June through September, the net input of 

 energy from the surface of the ocean in this region will depend significantly 

 upon the frequency and distribution of such synoptic scale disturbances. 



Detailed analysis of the tropical Atlantic for the International 

 Geophysical Year of I958 is being carried out by Dean ( Dean and La Seur, 

 work in progress in Dept. Meteor., Florida State lAilv.). The frequency of 

 equatorial vortices for each month in 1958 has been obtained. Preliminary 

 results suggest a frequency of 10 to 15 vortices per month during August, 

 September, and October. As shown in Figure ik, development generally takes 

 place off the West African coast in the vicinity of 5°N to 10°N, with some 

 vortices api>arently emerging from the continent itself. As the equatorial 

 trough region migrates equatorward, the number of vortices diminishes and 

 they can be tracked into the Atlantic for limited distances only. During 

 the months of January and February, only a few weak vortices appear in the 

 eastern equatorial Atlantic, none of which migrates into the central 

 Atlantic. Phenomena In the mid- and upper- troposphere (such as the tropical 

 easterly jet) appear to play an Important role in this seasonal fluctuation 

 in the frequency of these equatorial systems. Figure ik shows the tracks of 

 11 equatorial or tropical cyclones. At least nine of these systems followed 

 a track confined to an extremely narrow belt. As shown by Figure 15, the 

 mean map reflects this concentration as an asymptote in the streamline field. 



For the region near the asymptote, a mean number of 10 vortices per 

 month can be accepted for the wet season months (July through October), with 

 1 to i<- per month during the dry season (January through May). If, in the 

 mean, the disturbance covered 15 x 15 degrees of latitude and moved at a 

 mean rate of 3OO nautical miles within 2i^ hours, or 5 degrees of latitude 

 per day, then within a belt 15 degrees wide across the tropical Atlantic 

 centered on the mean asymptote during any wet season month, the mean 

 sensible and latent heat flux would correspond to the values computed for 

 the composite storms. The choice of a belt 15 degrees wide is suggested 

 not only by the mean size of the disturbances examined, but is also reflected 



