118 MALKUS [chap. 4 



a. Distribution of evaporative heat flux 



Fig. 7 was obtained using 650 oceanic sites, in 5° latitude and 10° longitude 

 intervals. Its main features are : 



(i) Very high evaporation in the subtropics and trade-wind regions, ranging 

 between 80-120 kg cal/cm^ year or 250-375 cal/cm^ day. The isopleth 120 kg cal/ 

 cm 2 year means 2 m of ocean water per cm 2 of surface are lost annually. 



(ii) Slight diminution in evaporation toward the equator. 



(iii) Rapid diminution in evaporation poleward, except for very high values 

 near the western ocean boundaries. 



(iv) Pronounced non-zonal changes in evaporative heat loss such that local 

 Qe values may depart from the latitudinal average by a factor of two or three. 



The main reason for non-zonal changes in heat losses for evaporation is the 

 presence of warm and cold sea currents. All principal warm currents, such as 

 Gulf Stream, Kuroshio, Brazilian Current, etc., are associated with local 

 maxima in Qe, while cold currents, like the Canary, Benguela, California, 

 Peruvian and Labrador Currents, are associated with low Qe or equatorward 

 dips in the isopleths. The main difference, however, between the Qe pattern of 

 Fig. 7 and that of Jacobs is the relative diminution here of these longitudinal 

 anomalies due to ocean currents. In Jacobs' figure (which covers only the 

 Northern Hemisphere) the Gulf Stream peak, for example, exceeds the tropical 

 North Atlantic values by nearly a factor of two rather than 20% and the 

 Kuroshio peak is far more pronounced than that shown in Fig. 7. 



Besides the sea currents, atmospheric circulations also contribute to geo- 

 graphic variations in evaporative heat loss. This effect is felt primarily through 

 changes in the radiation balance of the ocean surface (see equation (1)). For 

 example, due to increased cloudiness, the radiation balance of the ocean 

 surface diminishes slightly from subtropical to equatorial regions. In the 

 exchange formulas, this effect shows up in Qe and Qs by way of the diminished 

 sea-air temperature excess in equatorial regions as compared to the trades. 



b. Distribution of sensible heat flux 



Fig. 8 (obtained from the same computation points as Fig. 7) shows the 

 amount of sensible heat Qs that is emitted from the underlying sea surface to 

 the air (positive values) or is received by the surface from the air (negative 

 values). The most outstanding feature of Fig. 8 is that the major portion of the 

 ocean surface, on the average for the year, emits heat into the atmosphere. 



Over most of the ocean surface Qs, the turbulent heat flux, is small in com- 

 parison with the principal components of heat balance such as R and Qe, and, 

 except for parts of the North Atlantic, comprises not more than 10-20% of the 

 latter (Table V). High absolute values of turbulent exchange are reached in 

 regions where the water is, on the average, much warmer than the air, i.e., in 

 regions affected by powerful warm sea currents (such as the Gulf Stream) and 



