with Figure 1 reveals that the Icelandic low and the zonal westerlies are weaker and 

 are centered about five degrees further north in summer than in winter, while the 

 subtropical high dominates the circulation over much more of the Atlantic Ocean 

 in summer. In summer as in winter it is the weak circulation patterns which bring 

 the greatest departure of North Atlantic weather from the normal conditions as rep- 

 resented by the climatological charts. Consequently it is important to select a series 

 of synoptic charts which includes a period of summer low index conditions over 

 the North Atlantic. 



Of the sequence of maps which were selected for discussion here, the period 

 from August 20 to August 26 is one of typically weak circulation. The predominant 

 anticyclonic centers occur at northerly latitudes in the polar air masses, although 

 by the end of this period the polar anticyclones are deteriorating while the sub- 

 tropical Atlantic high is increasing. During this period the frontal systems over the 

 Atlantic and western Europe have principally a north-south orientation and move 

 slowly. The cyclonic centers are numerous and weak, and also move slowly along 

 the fronts. 



The period from August 27 to August 31, inclusive, is one of transition, 

 during which the trend is toward the establishment of large cyclonic cells at higher 

 latitudes with the elimination of the polar anticyclonic centers, and toward the 

 re establishment of a dominant subtropical high in the eastern Atlantic. By Sep- 

 tember 1 a typical summer strong circulation pattern is established, with two 

 moderately strong cyclonic centers at high latitudes and extensive zonal westerlies 

 north of latitude 45° N. This circulation pattern has reestablished an east-west 

 orientation of the frontal systems at higher latitudes, and the tendency to rapid 

 eastward movement of fronts and centers north of 45°. Only in the southwestern 

 Atlantic, the southeastern United States, and the Gulf of Mexico and Caribbean 

 area is there a marked hangover of typically weak circulation conditions. In this 

 region the subtropical high which dominates the eastern Atlantic is completely 

 broken up by two slowly moving tropical disturbances and one stagnant extra- 

 tropical cyclonic center, all of which behave with the indecisiveness which is so 

 typical of a low index circulation. Actually it reciuires another full week before 

 these disturbances are cleared out of the southwestern Atlantic, but otherwise the 

 entire first half of September is marked by an unusually strong state of the general 

 circulation for so early in the autumn. Especially over the North Atlantic and 

 northern Europe the storms during this period repeatedly reach intensities which 

 are characteristic of midwinter conditions. 



There follow a few brief remarks on each of the daily synoptic charts from 

 the selected summer sequence. On the map of August 20 the most striking weak 

 circulation features over the North Atlantic are the predominance of anticyclonic 

 cells in the northwestern and in the northeastern Atlantic, and the presence of a 

 frontal system extending from the Azores eastnortheastward over western Europe. 

 Exceptionally warm conditions prevail in central and western Europe south of this 

 front (cf. Figure 10). In summer at time of weak circulation the Polar Front in the 

 eastern Atlantic is more likely to extend eastnortheastward through central Europe 

 rather than to lie further south in the Mediterranean as it so frequently does in 

 winter. The preference for the Mediterranean in winter is doubtless due largely to 

 the relative warmth of this water body during the cold season, as well as to the 

 southward shift of the general circulation pattern in winter. 



It will be noticed that widespread fog is occurring in the vicinity of New- 

 foundland and the Canadian maritime coast. This condition is inevitable in this 

 region in summer when tropical maritime air is being transported northward over 



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