SECT. 2] LAKGE-SCALE INTERACTIONS 275 



the anomalous component. Thus an anomalous component from the south may 

 represent an increased southerly prevailing wind or may imply diminution of 

 the northerly wind which is normally present. 



The most consistent abnormality of the Northern Hemisphere's general 

 circulation during 1957 and early 1958 was low strength of the prevailing west 

 winds of mid-latitudes, or persistent low "zonal index" of the westerlies. The 

 subtropical anticyclones were weaker and more broken up than usual, and in 

 particular, the east-central Pacific showed a much deeper than normal low 

 pressure trough, which was pronounced throughout the period. 



This unusual trough, which during the fall of 1957 (Fig. 86) had a 190-ft 

 negative anomaly at 700 mb, means that over much of the area east of its 

 axis (165°W in the figure shown) the prevailing and resultant wind had a 

 stronger south to north component than normal. West of the axis, the reverse 

 anomalous conditions are implied. Experience suggests that these are composed 

 of repetitive northward thrusts of air in advance of the trough and southward 

 thrusts behind, as rapidly developing cyclones move into the Aleutian low 

 pressure cell, one of the atmosphere's persistent large-scale "centers of action". 



Namias first attempted to isolate and estimate quantitatively the advective 

 effect of these winds, to determine whether the major pattern and right order 

 of magnitude of the sea-temperature anomalies would result. He used Ekman's 

 empirical expression (Sverdrup, 1942) for the transport of water at 45° to the 

 right of the wind direction, due to its stress upon the surface layers, namely, 



vjw = 0.0127/sin'/2 cp, (72) 



where v is the speed of the surface water current, w is the wind speed and 99 the 

 latitude. This enabled him to compute surface-water displacement arrows, like 

 those in Fig. 87a, which, when superimposed on the normal sea-surface iso- 

 therms for the season in question, permitted computations of simple advective 

 changes with respect to seasonal normal. The result for fall, 1957, is shown in 

 Fig. 87b. The fact that there is some apparently real qualitative agreement with 

 the observed patterns of Fig. 85 is suggestive that an air-sea link on this scale 

 has been found, particularly in view of the drastic oversimplifications of the 

 approach. As the author points out, every other term in the energy budget 

 which would change the water temperature was set aside except advection, 

 and even that was treated crudely by starting every time from the seasonal 

 normal isotherms. 



The purely advective computation gave poorer results in summer when air 

 circulations were more sluggish, although the water-temperature anomaly was 

 undiminished. Namias then looked qualitatively at the divergence patterns of 

 the induced water movements and their effects upon upwelling, possible 

 changes in insolation and cloudiness associated with the weather patterns, and 

 evaporative differences due to weaker winds. These could not be combined into 

 a proper budget. Among the essential pieces of missing information was the 

 depth to which the ocean warming extended, although there was evidence that 

 it reached well below 100 m ; the latter rather ruled out observed insolation 



