424 Bigelow — Meteorological Elements of the United States. 



and the vapor pressure, hut an increase in the barometric pres- 

 sure. In the short-period curves the reverse of this is true in 

 the Pacific States, but the same rule holds good on the Rocky 

 Mountain plateau and eastward to the Atlantic Coast. An 

 increase of solar energy, as registered bj 7 the number of prom- 

 inences and the strength of the magnetic field, is attended 

 by direct synchronism of the temperature and its dependent 

 vapor pressure, but inverse or barometric pressure, in the Pa- 

 cific States. An increase of the solar output of radiation is 

 accompanied by a decrease in the temperative and vapor pres- 

 sure, but increase of the barometric pressure, to the east of the 

 Rocky Mountains. We already have shown* that the direct 

 sychronism between the prominences and the temperature 

 prevails thoughout the tropics, while the synchronism is 

 generally reversed in the temperate zones. The direct increase 

 of solar radiation is attended by diminution of temperature in 

 the greater part of the United States. Meteorologists are 

 familiar with the fact that the temperatures of the Pacific 

 States generally are the reverse of those in the central and 

 eastern districts, in the sense that the monthty residuals 

 usually have opposite signs, as can be seen on numerous 

 monthly maps representing these conditions for the years 

 1873-1905. 



It therefore is evident that this phenomenon of inversion is 

 to be explained only by the facts of circulation of the atmos- 

 phere. Since the high-pressure belt, separating the westward 

 drift of the tropics from the eastward drift of the temperate 

 zone, crosses the United States from Florida to Northern 

 California or Oregon, it follows that the Pacific States are 

 practically to be considered as a part of the tropical system, 

 so far as circulation is concerned. This is characterized by 

 freedom from cyclonic circulation, and by a quiescent state of 

 the atmosphere. On the other hand, east of the Rocky 

 Mountains the atmosphere is continually filled with cyclones 

 and high-pressure areas which advance down the slope and move 

 eastward. This is the result of well-known meteorological con- 

 figurations, which are determined by the relations of the general 

 circulation to the ocean and land areas. When the solar radi- 

 ation is stronger than the normal, it increases the tropical cir- 

 culation, with its currents directed poleward in the upper and 

 lower strata, and this is counterbalanced by return cold polar 

 currents, which flow persistently over the United States east- 

 ward of the mountains. This therefore conforms to our obser- 

 vations of the temperature, vapor pressure and barometric 

 pressure. The temperature observed in the temperate zones 



* Studies on the circulation of the atmospheres of the Sun and of the 

 Earth, Monthly Weather Review, November, 1903. 



