48 polar problems 



Arctic Influences on European Weather 



It is apparent that in winter Canada and the United States are 

 more directly affected by the meteorological conditions of the Arctic 

 Regions than is northwestern Europe, where, with the Gulf Stream 

 to the westward and the mean track of cyclonic areas west and north, 

 the Arctic effect is at least less potent. 



The year round, however, areas of high pressure forming in north- 

 ern latitudes and moving southward have a very important bearing 

 on the weather conditions of all the northern middle latitudes. They 

 form what the Norwegian meteorologists have termed a polar front.^ 

 The air within these boundaries is of a temperature acquired in higher 

 latitudes, and southerly currents set in motion by cyclonic areas over- 

 run the low-lying cooler air of the polar front and lead to the all- 

 necessary rainfall. Daily weather maps will show that the majority 

 of summer thunderstorms have occurred along a polar front. 



Factors Leading to the Development of 

 Cyclonic Areas in the North 



There has been much controversy as to the normal pressure over 

 the Polar Regions. Naturally, sufficient observations are lacking, but 

 at the present time general deductions may be made from the run of 

 the isobars drawn on the daily meteorological charts of the northern 

 hemisphere which are now available. Stations in northwestern Europe, 

 Spitsbergen, Iceland, and Greenland show the pressure distribution on 

 one side of the pole (Fig. 9). Stations in Alaska show the conditions 

 on the other side, and interpolation will usually give a fairly accurate 

 outline of the distribution over the polar area. There is, however, 

 in northern Russia and Siberia a wide gap which, it is hoped, will 

 sometime be filled in. Stations exist there, but it is only very occa- 

 sionally that reports from these stations come to England and France 

 and thence to America. 



The weather maps of the winter months show a persistent stream 

 of low areas approaching the northwestern coasts of Canada and 

 Alaska from the Pacific and passing into and perhaps across the con- 

 tinent, and another stream passing from the Gulf of St. Lawrence 

 south of Greenland and to the northwest of Scandinavia (Figs. 10-15). 

 The Polar Regions lie between these two streams; and there is strong 

 evidence that pressure there is normally higher than to the southward, 

 and it may be assumed that the winters are less stormy. 



But the meteorologists require further information, there, being as 

 yet so many points unexplained. One wonders why it is that in some 



' On this topic see the preceding paper by Mr. Clayton in the present volume and the references 

 there cited in footnote 6. A recent paper by V. Bjerknes entitled "Die Polarfronttheorie " is published 

 as part of the proceedings of the Nov., 1926, meeting of the International Association for the Exploration 

 of the Arctic by Airship in Erganzungsheil No. 191 zu Petermanns Mitt., Gotha, 1927, pp. S3-6o. — Edit. 

 Note. 



