Icelandic low moves rapidly eastward Into northern Asia. In other words, when a 

 weak circulation pattern is already established over Asia, a good kick from the 

 sudden intensification of the Icelandic low makes the low index pattern back up 

 into the Atlantic, and incidentally at the same time it reestablishes a strong circula- 

 tion in eastern Asia, but when the circulation pattern is already strong over Asia, 

 there is no reaction to the kick. 



As mentioned above, the maximum retrogression of the' Asiatic anticyclone 

 at high latitudes is to be seen on the map of January 19. Otherwise the significant 

 feature to be noted on this chart is the fact that at several points, both in the mid- 

 Atlantic and in eastern North America, currents of tropical air are beginning to 

 reach the higher latitudes as the warm sectors of northward moving disturbances. 

 The north-south orientation of frontal systems, and the northward or southward 

 movement of disturbances, is even more a part of the winter low index pattern than 

 is the east-west orientation of fronts and eastward movement of disturbances at 

 low latitudes. It is such north-south orientation of the frontal systems and of the 

 large scale air mass movements which leads to the extreme longitudinal tempera- 

 ture contrasts which characterize the winter type of weak circulation pattern, with 

 excessive cold in one meridional zone, excessive warmth in the next. 



On the map of January 20 the northward advance of tropical air in the mid- 

 Atlantic is seen to be progressing rapidly, so that some moderation of temperature 

 is setting in over the whole eastern Atlantic. The return of milder maritime polar 

 air masses to the most northeastern part of the Atlantic is made possible by the 

 clockwise turning of the isobars in that region as the continental anticyclone begins 

 to push actively southwestward. This southwestward extension of the anticyclone 

 combined with the continued cyclonic activity in the Mediterranean favors the 

 flow of cold continental polar air to extreme southwestern Europe and into the 

 Mediterranean. It is worth noting that the intensification of the continental anti- 

 cyclone along the west coast of Europe on January 20 and 21 accompanies the 

 establishment of a broad zone of rather strong southerly winds in the eastern and 

 central Atlantic, winds which are produced by the deepening disturbances that are 

 moving northward on these two days in the central and western Atlantic. 



There is little to be remarked on the map of January 21 other than the 

 continuation of the trends noted on the previous day, especially the northeastward 

 movement of warm air over the central and eastern Atlantic, the southwestward 

 flow of cold air over southwestern Europe, and the continuation of cyclonic activity 

 in the Mediterranean with widespread snow in central Europe. It will be noticed 

 that in general dense surface fog is seldom reported in the maritime tropical air 

 masses moving northward over the oceans in winter. This is much more likely to 

 occur over a continental area, as evidenced by the widespread air mass and pre- 

 frontal fog in the eastern United States on this day. In summer the conditions are 

 reversed, with the principal incidence of tropical air fog occurring over the cold 

 water areas. 



The map of January 22 shows the continued stagnation of a typical weak 

 circulation pattern from North America to Europe, with the north-south orienta- 

 tion of the principal frontal systems and the slow northward advance of disturb- 

 ances in the mid-Atlantic. It is noteworthy that the southwestward thrust of the 

 continental anticyclone that accompanied the anticyclogenesis along the west 

 coast of Europe on January 21 and 22 is now completed. This is significant in that 

 it suggests that the reestablishment of the Azores high is not yet to occur, and 

 consequently that a low index weather i^attern in the Atlantic may be expected 

 to persist for some time longer. 



50 



