6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



A later investigation disclosed that there were also latitude dif- 

 ferences in pressure correlated with changes in the monthly num- 

 ber of sun spots.' Using the data from about 200 stations, the aver- 

 age pressure when sun spots were near their maximum frequency 

 was compared with the average pressure in the same latitudes when 

 the sun spots were near a minimum of frequency and differences 

 obtained. These differences are plotted in figure 4. 



Figure 4, shows that when sun spots are more frequent in num- 

 ber, the pressure is lower in the equatorial region from about 30° N. 

 to 30° S., while from about latitude 35° to 65° in both hemispheres, 

 the pressure is higher when the sun spots are most numerous. This 

 result is in good agreement with that found for short period changes 



NORTHERN HEMISPHERE 

 70° 60° 50" 40° 30° 



•m-fr. 



+ 0.6 

 + 0.4 

 ♦ 0.2 

 0.0 

 -0.2 

 -0.4 

 -0.6 



EQUATOR 

 10° 0° 10° 



SOUTHERN HEMISPHERE 

 5° 30° 40* 50* 60' 



Fig. 4. — Mean difference of pressure at sun-spot maximum from that at 

 sun-spot minimum. 



of solar radiation and with the fact disclosed by the measurements 

 of the Smithsonian Astrophysical Observatory that more radiation 

 from the sun reaches the earth when sun spots are more frequent. 

 A recent research by Ekhart ^ shows clearly the opposing oscilla- 

 tions of the pressure in high and in low latitudes. When the pres- 

 sure falls in low latitudes, it rises in high latitudes and vice versa. 



In order to investigate this relation further with the data which 

 appeared in " World Weather Records," ^ 24 cases were selected in 

 which solar activity was above normal as shown both by the Wolfer 

 sun-spot numbers and by the Smithsonian values of solar radiation ; 

 and 24 cases where the opposite condition prevailed, namely, a small 

 monthly sun-spot value and a low value of solar radiation. Where 



' Clayton, H. H., World Weather, p. 262. New York, Macmillan & Co., 1923. 

 "Ekhart, E., " Untersuchungen der jiihrlichen Schwankungen der atmosphar- 

 ischen Zirkulation," Meteorologischen Zeitschrift, Heft 2, February, 1930. 

 ^ Smithsonian Misc. Coll., Vol. 79, 1927. 



