230 



MALKUS 



[chap. 4 



cumulus minima on both the diurnal and synoptic scales (see also curve for 

 Period C, Fig. 61) are periods where the sea-air temperature difference has 

 become negative, so that Qs is reversed. 



In analyzing the results of the Crawford cruise, particular attention was paid 

 to the most pronounced disturbance of the period. Consisting of an equatorial 

 vortex, which set off an easterly wave to its north (Fig. 57), it showed con- 

 vergence of 5-10 X 10"5 sec~i in the area around its closed center. Winds in this 

 region were light and variable, rising occasionally to 7-8 m/sec in the inter- 

 mittent showery "squall lines". In the twenty-four hours as the center passed 

 the ship station, 41.4 mm of rain fell, or more than half the total precipitation 



Hours (LST) 



Fig. 65. Diurnal march of low cloud cover (cumulus) in oktas during Crawford equatorial 

 Atlantic cruise. Estimated from shipboard by trained weather observers. (After 

 Garstang, 1958, unpublished.) 



of the sixteen-day period. In this convergent zone, the sensible heat input, Qs, 

 averaged 21.8 cal cm"2 day~i or nearly twice the disturbed period mean of 

 Table XVI. Since the corresponding Qe was 227 cal cm~2 dayi, the Bowen 

 ratio was nearly 10%, in contrast to its value of less than 2% in the normal and 

 fair periods. 



These results suggest that in the equatorial zone and quite probably 

 throughout the tropics, the sea-air flux of sensible heat is concentrated in 

 disturbances, where it may reach or exceed 10% of the normal Qe. In equatorial 

 regions these disturbances are sufficiently common so that their contribution 

 to the average heat flow should not be ignored. Mechanistically, the enhanced 

 Qs comes about through increased sea-air temperature difference, which more 

 than compensates the light winds near the centers of weak- to -moderate 



