NO. 15 WEATHER AND SOLAR ACTIVITY CLAYTON 7 



longer oscillations of pressure at Colombo are exactly opposite to 

 those at Upernivik in Iceland and at Yakutsk in Siberia, and the trend 

 of the pressure for the past 42 years is opposed. The comparison of 

 Colombo with Laurie Island, the most southern station in the Southern 

 Hemisphere, in the lowest curve in figure 5 shows that the pressure 

 oscillations of long period in high latitudes in the Southern Hemi- 

 sphere are also opiX)sed to those at Colombo' and are similar to those 

 in high latitudes in the Northern Hemisphere. It should be noted 

 that Colombo is only about 7° of latitude from the Equator and is 

 within the warmest and most humid area of the earth, whereas 

 Upernivik and Yakutsk are in the coldest regions of the Northern 

 Hemisphere where the vapor content of the atmosphere is small. 



This comparison indicates that there are marked changes in the 

 Pole to Equator pressure gradients in the atmosphere and, hence, 

 marked oscillations in the intensity of the atmospheric circulation. 

 To this cause may reasonably be attributed the similarities of rain- 

 fall and temperature between such widely separated areas as the 

 United States and South America, the United States and Australia, 

 and the similarity between the pressure in the Indian Ocean and the 

 temperature on the coast of Chile. 



The general diminution in the pressure gradient between high and 

 low latitudes during the past 42 years, as shown by the trend of the 

 pressures in high and low latitudes, is indicative of a world-wide 

 amelioration of climate during the same period. It has been pointed 

 out by various research workers that glaciers in high latitudes are 

 slowly retreating, that the waters in the Great Lakes and in other 

 lakes farther west in the United States are receding to lower levels, 

 and that there is an upward trend of the temperature in high latitudes 

 in both hemispheres. This change has probably been in progress 

 during most of the past century. The latest publication on this 

 subject is by Kincer in the Monthly Weather Review for September 

 1933. These various researches indicate that the climate of the earth 

 is on the whole becoming warmer and drier in some long period of 

 solar change, the length of which is not yet known. The change of 

 climate corresponds in character with the long-period oscillations of 

 past epochs pointed out by C. E. P. Brooks, of London, in his book 

 " Climate Through The Ages." 



When the departures from normal pressure are plotted on charts, 

 they are seen to be larger in certain regions than in others. The regions 

 of greatest departure have been called centers of action, but they 

 are not fixed in position. This fact is evident from figure 6. This 

 figure gives a comparison of the smoothed annual means of pressure 



