302 ANNUAL REPOPvT SMITHSONIAN INSTITUTION, 19 3 



As noted by Clayton, the monthly means of solar radiation and 

 those of temperature and pressure show that with an increase in in- 

 tensity of solar radiation the maxima of pressure form over the 

 coldest parts of the temperate zones, which are the continents in 

 winter and the oceans in summer. The more intense the radiation, 

 the farther north and south are these maxima of pressure formed. 

 The abnormal distributions of temperature and precipitation are in- 

 timately related to the distribution of pressure. Thus the centers 

 of action move north and south of their mean position with the vary- 

 ing intensities of solar radiation. There is a lag in the solar effect 

 near the centers of action proportional to the duration of the solar 

 change. In general the lag is about one-tAvelfth of the length of the 

 interval from maximum to maximum or minimum to minimum. 

 The lag may vary from a few hours to a year, depending on the 

 duration of the effect. 



The year-to-year variations in solar radiation are shown by Clay- 

 ton to be connected with year-to-year variations in rainfall and river 

 heights in North America, South America, and Australia. He also 

 observes that the solar measurements clearly indicate the existence 

 of a 3 to 4 year change in solar radiation, which is reflected in a 

 3 to 4 year change in pressure, rainfall, etc. This he attributes to 

 a variability in the intensity and amount of faculae on the surface 

 of the sun. 



Clayton's studies of the effect of maximum and minimum sun-spot 

 periods on the weather show that the pressure is lower at the time 

 of maximum sun spots in the equatorial zone, especially in the humid 

 regions, at all times of the year. The differences of pressure are, 

 however, much less than in the case of the monthly means. Koppen 

 has shown that the mean temperature of the surface air over the 

 globe was lower at sun-spot maximum than at sun-spot minimum. 

 Although much has been written concerning the effect of sun spots 

 on the weather, investigators agree that weather conditions are far 

 more variable than sun-spot numbers. 



RECORDS OF WEATHER CHANGES EXTENDING OVER MANY YEARS 



Weather changes extending over long periods of time are reflected 

 in the annual growth rings of trees (Douglass, 1909, 1914, 1919, 1928, 

 1929; Huntington, 1914). Harris (1926), in considering the correla- 

 tion between sun-spot numbers and tree growth, concludes that the 

 coefficients indicate a low positive correlation between them, but the 

 relationship is by no means so intimate as many writers imply. 



The best-preserved records of weather affecting glaciation are 

 found in the aqueo-glacial deposits of Pleistocene age, which pre- 

 serve seasonal, annual, and longer period variations. The deposits 

 are commonly known as laminated or varved glacial clays. 



