NO. 15 WEATHER AND SOLAR ACTIVITY CLAYTON 33 



Equator indicates widespread oscillations in the circulation of the 

 earth's atmosphere. In addition, for the past 42 years covered by 

 the observations, there has been an upward trend of pressure in the 

 equatorial belt and a downward trend in the cold areas of high lati- 

 tudes, indicating a generally decreasing pressure gradient between 

 high latitudes and the Equator, and an amelioration of the earth's 

 climate. 



2. In all latitudes, changes in pressure, temperature, and rainfall 

 are most intense in certain areas, which have been called centers of 

 action. In the equatorial region the centers of action are over the 

 Indian Ocean and over the equatorial Atlantic between the Gold Coast 

 of Africa and the Amazon River. In higher latitudes there are centers 

 of action in the North Atlantic and North Pacific in which the pres- 

 sure and rainfall change in the same way as in the equatorial centers 

 of action. 



Oppositely behaving centers of action are found over the cold lands 

 of high latitudes such as Iceland, northern Canada, and northwestern 

 Siberia, and over the cool waters of the middle latitudes such as the 

 Pacific Ocean west of lower California and west of Chile and in the 

 Atlantic ocean west of northern Africa. When the pressure and rain- 

 fall are in excess in this latter group of centers of action they are 

 in defect in the equatorial and oceanic centers. 



3. These centers of action are related in a general way to such 

 major features of the earth's surface as the polar regions and the 

 equatorial region and the distribution of land and water. Within 

 regions of warm water and of high vapor content in the equatorial 

 region, and over the oceans in high latitudes, the weather conditions 

 in general oscillate oppositely to those over the cold land areas in high 

 latitudes and the cool water areas of lower latitudes. These latter 

 regions are also regions of low vapor pressure. 



4. The centers of action are not stationary but tend to shift posi- 

 tion, oscillating to and fro over wide areas, so that any given place on 

 the earth's surface may be at one time within the influence of a field 

 of action of one kind, and at another time under the influence of a 

 field of action of an opposite kind. 



This shifting of the centers of action in the atmosphere has been 

 one of the most disconcerting and discouraging facts confronting re- 

 search workers in meteorology. Relations have been found between 

 distant regions which for a while gave high correlation coefficients. 



