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temperature of the land and that of the ocean, and therefore there will be no region 

 where air will be rapidly heated or cooled. A comparison of Figure 6 and Figure 10 

 shows that in northern latitudes the air temperature is slightly higher than the 

 ocean temperature. 



(6) Figures 9 and 11 represent the distribution of temperature in spring and 

 fall, respectively. In general the spring map is similar to the summer map, while 

 the fall chart more closely resembles the winter chart. 



(7) In all seasons a temperature trough is observed about longitude 50° W 

 and east of Newfoundland. This is a result of the southward flow of cold water — 

 Labrador Current — as shown in Figure 3. 



6. Temperature Extremes. 



Figures 12 and 13 give an estimate of mean low air temperatures in winter 

 and summer. These charts have been drawn on the basis of observations of the 

 average temperature in direct polar and arctic air outbreaks. The isotherms were 

 obtained from charts drawn by Petterssen^ and minor adjustments were made 

 after a study of Northern Hemisphere weather maps. The dotted line in Figure 12 

 is intended to indicate the southernmost limit of the 0° C isotherm in any winter. 



It will be seen that the orientation of isotherms is similar to Figures 8 and 

 10. The lowest temperatures are observed in the western Atlantic as a result of 

 the cold outbreaks which originate in the Hudson Bay region. The southward dip 

 of the isotherms in the North Sea in winter is due to the proximity of the cold land 

 masses. 



7. Frequency of Gales. 



The frequency of strong surface winds has been indicated in Figures 14 and 

 15 for February and August respectively. The data for these charts was obtained 

 from the Climatic Charts of the Oceans,^ and the isolines represent the percentage 

 frequency of winds of Beaufort Force 7 or higher. 



It is evident that the most frequent period of strong winds is found in winter. 

 The strong winds are associated with the deep cyclones of the Icelandic system 

 which is shown in Figure 1; the maximum frequency appears centered southeast 

 of Greenland. The maximum in the western Atlantic is probably the result of the 

 strong winds north of the mean position of the Polar Front, as shown in Figure 16. 

 Figure 2 shows a much weaker circulation, and we see from Figure 15 that gales 

 are much less frequent in summer than in winter. Gales are comparatively rare in 

 low latitudes, due to the presence of the subtropical anticyclone. 



In view of the lack of data the charts were not extended beyond 60° N. 

 However, from a study of Figures 1 and 2, it would be expected that the isolines 

 would be approximately parallel to the Norwegian coast. Probably the region of 

 maximum frequency would be located to the north of mean position of the Arctic 

 Front in Figure 16. 



8. Mean Air Currents and Air Masses over the Atlantic. 



T. Bergeron^ has investigated the mean position of air masses over the 

 Atlantic in winter, and his conclusions are presented in Figure 16. The wind 

 arrows on the chart were obtained from Schott^ The fronts are the mean position 

 of non-occluded fronts. The percentage frequency lines represent the percentage 

 of days when non-occluded fronts were located within the nearest 5° square during 

 January and February for the years 1933 to 1935. 



