SECT. 2] LARGE-SCALIi INTERACTIONS 207 



19° 30'N, 66°W) ill the western Atlantic trade. However, the Woods Hole ship 

 alst) visited the eastern Pacific Ocean, south of the Panama Canal Zone where 

 the air is warmer than the sea. Comparison of the traces obtained there (Fig. 

 51b) with those obtained in the Caribbean is startling. The fluctuations have 

 almost disappeared; temperature and wet bulb^ are nearly constant. Vapor 

 pressure of sea and air are almost identical, and there is little or no latent heat 

 transfer. The sensible heat flow will be downward, but since the air is stabilized 

 from below, the energy exchange becomes extremely small at the prevailing 

 wind speed (~15 knots). Fig. 51 should be compared with Figs. 18 and 19 

 which contrast the annual marches ofQs and Qe consequent upon these different 

 air-sea boundary structures. 



On inspecting Fig. 51a, we observe a distinct but not perfect positive correla- 

 tion on the 50-300 m eddy scale between temperature and moisture, and a 

 negative correlation between these and wind speed, supporting our mechanistic 

 picture. In the longer "eddies", temperature and moisture variations appear 

 to be out of phase. The Woods Hole aircraft data extend the picture and bring 

 in the missing link of vertical motion. Traverses, flying as low as 50 ft over the 

 sea, were made while recording horizontal and vertical motion, temperature and 

 moisture simultaneously, with a resolution of one-fifth second ( ~ 10 m distance), 

 except for moisture which was averaged over one second ( -^ 50 m). Correlation 

 of ascending speeds of 20-50 cm/sec with warm, wet eddies of deficient horizontal 

 speed was established in the lowest 300-500 ft of the sub-cloud layer. Fluxes of 

 sensible heat, latent heat and momentum have been calculated directly from 

 these records (see Bunker, 1960) using equations (22)-(24). It was established 

 that in all but the lowest strata, the major transports in the layer below cloud 

 base are effected by the 50-300 m eddies described and made visible by the 

 smoke in Figs. 48 and 49. 



As the fluctuation amplitudes in Fig. 51a indicate, by far the largest fluxes 

 effected by boundary turbulence are the upward transport of latent heat and 

 the downward transport of momentum. Temperature fluctuations are normally 

 small and the sensible heat flux is 2-10% of the latent, only marginally adequate 

 to balance radiation losses below cloud base. In undisturbed conditions, in fact, 

 it frequently reverses sign in mid-layer, becoming downward above about 

 500 ft. Yet we have seen from Fig. 51b that the ocean surface must be some- 

 what warmer than the air in order for the transport-producing eddy motion to 

 occur at all ! This implies the existence of a sensible heat flow. The air rising 

 from the sea is a little warmer than its surroundings and is thus slightly buoy- 

 ant. A temperature excess of 0.1 °C has the same effect in decreasing air density 

 as does a moisture increment of 0.6 g/kg. Both amounts are in the range of 

 observed fluctuation amplitudes : it therefore follows that the sensible heat 

 flow has at least as much influence on the stability, and therefore, on main- 

 taining the low-level turbulence, as does the water-vapor flow with its much 

 larger energy content. Thus the sensible heat exchange plays a major part in the 



1 Change of 1°F in wet bulb temperature, T^;, under these conditions corresponds 

 roughly to a change of 1.2 mb in vapor pressure or 0.75 g/kg in specific humidity. 



