246 



THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



far as the production of corn was concerned, extremely anti-pleionic or "lean" conditions 

 prevailed over most of the United States, which means that there was an especial deficiency 

 in the rains of June and July. In 1906, on the contrary, only one small area was lean, and 

 even there the deficiency was less than 2.5 bushels per acre. Throughout all the rest of the 

 country "fat" conditions prevailed— that is, the crop was better than the average. 



Figures 79 and 80, for the years 1908 and 1909, illustrate an interesting feature of the 

 pleions and anti-pleions of all sorts of meteorological phenomena, namely, their persistence 

 from year to year in spite of certain changes in form and location. The large anti-pleion 

 in the center of the United States in 1908 has contracted in its east-and-west dimensions 

 and has moved south in 1909, but it is clearly recognizable. In similar fashion the minute 

 anti-pleion over Delaware in 1908 has expanded over New Jersey, Pennsylvania, Maryland, 

 and part of Virginia in 1909. 



This emphasizes a most characteristic and important feature of the pleions and anti- 

 pleions— that is, their movabihty. By means of a series of monthly charts based on over- 

 lapping means for 12 months and thus eliminating all variations due merely to the succession 

 of the seasons, Ai-ctowski has discovered that a given pleion may last for many years, during 

 which its center moves back and forth in irregular curves whose north-and-south component 

 apparently exceeds the east-and-west. Sometimes they grow weak and tend to divide 

 into two or more sections, and practically disappear, while again they strengthen and 

 gather into strongly localized areas of pronounced intensity. Just where they originate or 

 how they disappear is not yet clear, but apparently they do not often pass from the sea to the 

 land. This much, however, is certain: they are a pronounced feature of continental and 

 perhaps of oceanic climates, and deserve most careful study, since in them may lie the key 

 to the prediction of the character of a season— months or even a year or two beforehand. 



For our present purpose another phase 

 of Arctowski's study of pleions and anti- 

 pleions is particularly important. In his 

 article on Arequipa* he shows that the 44 

 values of the "solar constant" as measured 

 by Abbott and Fowle between October 9, 

 1902, and May 14, 1907, agree in general 

 with the departures of the mean monthly 

 temperature from the normal at Arequipa. 

 This appears in figure 81, where the upper 

 curve shows the changes of the solar con- 

 stant in calories and the lower the depar- 

 tures of atmospheric temperature at Are- 

 quipa. To quote Arctowski : 



" It is obvious that the number of observa- 

 tions of the 'solar constant' is insufficient to 

 show all the details of the variation. More- 

 over, some measurements may have been taken 



precisely on exceptional days, giving values which would not have very greatly influenced results 

 of continuous records. Special meteorological conditions may also have influenced the obtained 

 figures. But, taking the uncertainty of the results into account, it is astonishing to see such a 

 close agreement between the two curves. * * * Supposing that the fluctuations of the 'solar 

 constant' and those of the monthly means of temperature observed at Arequipa coincide, which 

 is far from being certain, as the diagram shows that a delay is more probable, I compared the 

 Mount Wilson measurements with the Arequipa monthly departures of temperature. To have 



Fig. 81. — Variations of Solar Constant (upper line) and 

 Monthly Departures from Mean Temperature at Are- 

 quipa (lower line), after Arctowski. 



*The Solar Constant and the Variations of Atmospheric Temperature at Arequipa and some other stations. 

 Bulletin American Geographical Society, vol. 44, 1912, pp. 598-000, 



