REPORT ON ATMOSPHERIC CIRCULATION. 53 



Iceland to the south of Greenland. It is this region of low pressure which gives to 

 Western Europe its prevailing south-westerly winds and to North America its north- 

 westerly winds in winter. By these the temperature of Western Europe is abnormally 

 raised by its prevailing winds coming from the ocean and from lower latitudes, and the 

 temperature of North America is abnormally lowered by its prevailing winds coming 

 from Arctic regions and from land in the season when the effects of terrestrial radiation 

 are at the maximum. The opposite action of these winds, which are component parts 

 of the same atmospheric disturbance about Iceland, is shown by the temperature on the 

 coast of Labrador being only — 13°, whilst in the same latitude, in mid- Atlantic, it is 45°, 

 or 58° higher. This low-pressure region extends eastwards beyond Nova Zembla, and 

 from the resulting winds which follow that extension the rigours of the winter climate 

 of the north of Russia and Siberia as far east at least as Cape Severo are materially 

 counteracted. 



The remaining cyclonic centre is in the North Pacific, the lowest isobar being 

 29'55 inches south of Alaska. The effects of this low pressure on the prevailing winds, 

 and through these on the temperature and rainfall of the north-east of Asia and the 

 north-west of America, is exactly similar to the effects of the low pressure of the 

 Atlantic on the climates of Europe and the United States. 



The influence on the pressure of the Spanish and Italian peninsulas on the one 

 hand, and on the other the influence of the Mediterranean, Black, and Caspian Seas is 

 strongly marked ; and equally so do the Arabian Sea, India, and the Bay of Bengal leave 

 their mark on the isobars and the winds. 



February. — The distribution of temperature in this month is similar to that 

 of January, the chief difference in the northern hemisphere being that in inland 

 situations the influence of the returning sun begins to be distinctly felt in the higher 

 temperatures which now prevail ; whereas over the sea and in insular situations, 

 particularly in the higher latitudes, temperatures are even lower than in January, it 

 being in this month that the temperature of the sea falls to, or nearly to, the annual 

 minimum. At Werkojansk the mean temperature has risen from — 61°'2 to — 51 c, 9 ; and 

 the greater strength of the sun's rays is also well seen in the altered form and positions 

 of the isothermals in the continental regions of North America between lat. 20° and 40°. 



The great changes in the distribution of pressure in this month are a considerable 

 diminution over North America south of lat. 50° ; in the western part of the North 

 Atlantic, and over the whole of that ocean between lat. 40° and 60° ; over Africa, except 

 the south ; Europe, except north of a line from the south of Scotland eastward to Wiatka 

 in Russia, and thence northward to the Arctic Ocean ; all Asia, except the islands on its 

 east coast, and the north-east of the continent. Elsewhere pressure has risen, notably 

 in the eastern half of the Atlantic, south of lat. 40°, resulting in the formation of an 

 anticyclonic region, which is further developed in the following months; over 



