The extreme characteristics of the temperature anomaly pattern produced 

 over the eastern Atlantic and western Europe by the meridional character of the 

 persistent low index circulation is seen most clearly on the maps of January 23 and 

 24. A comparison of the temperature distribution presented by these charts with 

 the normals (see Figure 8, February differs little from January) shows that whereas 

 in France, Germany and central Europe the temperatures are 10° to 15° C below 

 normal, in the region from Iceland northwestward to North Cape and Bear Island 

 the temperatures are about 10° C above normal. The air mass in this northern 

 area is really tropical in character. The influence of this warm air has already carried 

 eastward to northwestern Russia. 



Another significant feature of these two charts is the steady development of 

 a closed cyclonic center near the Azores, and the development of a low pressure 

 trough with a suggestion of frontogenesis thence eastward to Gibraltar and the 

 Mediterranean. This trend in the development of the circulation pattern prac- 

 tically guarantees a low index pattern in the eastern Atlantic for some time to 

 come. Actually strong cyclonic activity from the Azores to the Bay of Biscay and 

 the western Mediterranean continued for a full week after this date. At the same 

 time an extremely intense and nearly stationary low formed off the east coast of 

 the United States. It was not until the first of February that the Azores high 

 became reestablished in the eastern Atlantic, and that the storm in the western 

 Atlantic moved northeastward to the point of regenerating the Icelandic low in its 

 normal position. These developments finally terminated the low index pattern 

 over the North Atlantic and western Europe, and marked the return of the more 

 normal strong circulation pattern characterized by the rapid eastward or north- 

 eastward movement of strong disturbances across the northern ocean. 



C. The Summer Period, August 20-September 3, 1932. 



The general circulation of the northern hemisphere, as represented by the 

 zonal westerlies of middle latitudes, is consistently weaker in summer than in winter, 

 and displaced somewhat northward. One consecjfuence of the weakness of the 

 general circulation in summer is a lack of the extreme and clearly contrasting pat- 

 tern types that occur in winter in such characteristic form. The cyclonic and anti- 

 cyclonic cells of the general circulation pattern tend to be more numerous, more 

 scattered and less intense than in winter, while the migratory centers tend to move 

 more slowly. However, there remains enough characteristic difference between the 

 weak and the strong circulation patterns to make the distinction significant. 



Other than the relative weakness of the circulation patterns in summer 

 compared with those in winter, the principal difference between the warm and the 

 cold seasons lies in the reversal of the monsoon influence. In summer the principal 

 Aleutian and Icelandic centers at time of strong circulation are displaced or develop 

 much more easily over the northern continental areas than they do in whiter. On 

 the other hand the strongest polar anticyclonic centers at time of minimum index 

 are much more likely than they are in winter to be located over the northern 

 ocean areas instead of over the continents. Thus in summer the polar highs fre- 

 quently merge imperceptibly into the subtropical highs which always tend to 

 remain over the oceans, but which are normally more intense and centered at higher 

 latitudes in summer than in winter. 



The normal summer weather conditions over the North Atlantic, as repre- 

 sented by the mean charts for August, conform at this season as in winter essen- 

 tially to the strong circulation pattern in modified form. Comparison of Figure 2 



51 



