192 



[chap. 4 



from the twelve-hour pilot balloon observations, but daily values of vertical 

 motion, w, were not available. The vertical transport terms were thus computed 

 from the average vertical motion deduced from the divergence field of Fig. 31d. 

 As the results will indicate, this approximation is not likely to be important. 



Fig. 45 shows the momentum budget of the Pacific trade section : the lowest 

 stratum, 1020-960 mb, is the sub-cloud layer. The next two (cf. Fig. 31a), 

 960-880 mb and 880-800 mb, include the cloud layer while the top one, 800- 

 720 mb, is everywhere above the inversion base. The solid arrows are the 



Pressure Production = 



Pressure Production 



12 



Pressure Production = 26 



Pressure Production = 2.7 



P 



mb 

 720 



Unit; 10 g cm sec" 



Fig. 45. Momentum budget of air flowing along Pacific trade trajectory of Fig. 31. Vertical 

 co-ordinate is pressure in mb. Upstream end denoted by u.s. ; downstream end by 

 d.s. Lowest layer (1020-960 mb) is sub-cloud layer. Middle two layers (960-880 mb 

 and 880-800 mb) include the cloud layer, while upper layer (800-720 mb) is every- 

 where above inversion base. Terms in momentum -budget (unit 10^ g cm sec-2) 

 evaluated using equation (36) as described in text. Solid arrows are transports by 

 mean motion. Dashed arrows are contributions of turbulent-convective ^hearing 

 stresses; bottom one found from equation (17), remaining ones as residuals for 

 balance. Arrow directed out of box denotes export of easterly momentum. 



transports by the mean motion. The production term is evaluated from the 

 observationally known pressure field. The dotted arrows are turbulent- 

 convective stresses. Only the bottom one, the easterly momentum input to the 

 sea, was directly computable; it corresponds to a shearing stress of 1.8 dynes/ 

 cm2, a rather large value due to the high choice of cd. The main physical 

 results would not be altered by dividing it by two, more plausible in view of 

 Figs, 6 and 40. The remaining stress terms were found as residuals to complete 

 the balance in each layer, beginning with the bottom. 



There is a vertical turbulent transfer of appreciable magnitude which, 

 as it should, changes sign at the east-wind maximum just above cloud base 



