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[chap. 4 



to a similarly averaged large-scale ocean-temperature pattern. He then supposes 

 that if the normal ocean thermal structure is related to the normal atmospheric 

 circulation, anomalous air circulations must give rise to anomalous conditions 

 in the sea. The time scale of the variations is particularly suggestive. Short 

 period, synoptic-scale fluctuations in air circulation, while large, change 

 radically from one day to the next. Thus, while they may produce substantial 

 changes in the surface waters, these are likely to be variable and conflicting, and 

 so cancel out with time. However, "regimes" in which certain aberrant forms 

 of atmospheric circulation persistently recur for months or longer have been 

 recognized (Namias, 1953). Such sustained abnormal winds might alter the 

 surface-water transports, divergence, radiative and exchange processes, 



Fig. 85. Observed mean sea-surface temperature anomaly (°F) for fall, 1957. (After Namias, 

 1959, Fig. 4.) 



Shading represents above -normal temperatures. 



creating thereby surface-temperature anomalies which might in turn help 

 maintain the abnormal air circulation and thereby themselves. 



To examine the eastern Pacific warming in this framework, Namias first 

 looked at seasonal averages of the overlying air circulations during the years 

 1957-58 and their departures from the long-period normals for each season. 

 An example for fall 1957 is reproduced in Fig. 86. With the geostrophic 

 relationship, we may deduce from these charts the prevailing winds for the 

 season and their departure from normal, recalling that looking downstream 

 the low pressure or height lies to our left, and speed is proportional to the 

 crowding of the isopleths. The isobars at sea-level (or contours of the heights of 

 the 700-mb surface aloft) thus give a measure of the total resultant or pre- 

 vailing wind for the season, whereas the isopleths of anomaly represent just 



