162 



MALKUS 



[chap. 4 



■=■ e 



7654 

 m/sec WSW 



2000 1500 1000 500 0654 



(km) '*— ENE m/sec 



2 4 6 



(a) 



2 1 



(b) 



(0 



0.2 0.6 ,^6 - 

 10 sec 



Divergence ~ h~ 



^ OS 



(d) 



Fig. 31. Atmospheric conditions along a trade-wind trajectory, from a study of the Pacific 

 trades. (After Malkus, 1956, Figs. 1, 2, 4 and 5a.) 



(a) Vertical structure of the air along the trajectory indicated in (c). Horizontal 

 distance given in km downstream of entrance end. Vertical co-ordinate to right in 

 mb, to left in km (approximate). The heavy lines separate the layers described in text. 

 The lines with arrows are trajectories while the lighter solid lines are potential 

 temperature isopleths labelled in degrees absokite. Trade cumulus clouds are entered 

 schematically. To the right is the profile of wind speed (along the section) at the up- 

 stream end and to the left is the wind-profile at the downstream end. Wind speeds 

 are in m/sec. 



(b) Graph showing observed net downstream warming in terms of potential 

 temperature increase. Ad, of the air parcels, calculated as a function of height by 

 following trajectories in (a). The dashed curve is a simple exponential used later in 

 the theory (see equation 42a, Section 6-C, page 196) to approximate the observed curve. 



(c) Solid line shows orientation of trade-wind trajectory in Pacific. The Hawaiian 

 Islands are shown at the down-wind termination, while the U.S. west coast appears in 

 the upper right-hand corner. The lighter solid lines are mean 700-mb contours (lO's ft, 

 first digit, a one, omitted), while the dashed lines are isopleths of gradient wind speed 

 (m/sec, positive values have component from west) and thus are parallel to the sea- 

 level isobars. 



(d) Horizontal velocity divergence (assumed equal to 8u/8s) calculated from ob- 

 served wind-profiles for Pacific trade trajectory, averaged over whole length of 

 section. Profile of 8u/ds shown as function of pressure on left and height on right. 



