158 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



botwcon -55° and -60° C. (-67° to -76° F.). Tho discovery of 

 tlio low toinpornturos aloft over tho equator serves to increase, 

 rather tiian duuinish, tho comploxitios involved in tho ac(0])tod theo- 

 ries of the n;oiioral circidation of tiio atmos])here. Another fact of 

 jijreat interest in connection with tho ii])per inversion is that its tem- 

 jierature, whilo practically constant from season to season, varies 

 greatly from ^ilaco to place and from day to day. Tn the United 

 States the mean of 50 ascensions made under the direction of the 

 Mount Weather Observatory, all of which entered the region, gives 

 for tho lower limit of the upper inversion a tom])erature of —52.1° C. 

 (-61.8° F.) regardless of season. The mean temperature of the 

 lower limit of the up])cr inversion, as deduced from the ascensions 

 made under the direction of Prof. Rotch at St. Louis, Mo., for all 

 seasons is —56.0° C. ( — 68.8° F.). The lower temperatures regis- 

 tered over St. Louis may be due in part to the latitude eflfect. The 

 mean temperature of tho upper inversion in Europe is not far from 

 -55°C. (-67°F.). 



It is said that in Europe the beginning of the upper inversion is 

 found at a less altitude over cyclonic than over anticyclonic areas; 

 also that it is higher in summer than in winter. In this country the 

 lower limit of the upper inversion does not appear to be at a less 

 altitude in cyclonic tnan in anticyclonic areas, although the evidence 

 is not absolutely conclusive either way. In the Huron series the 

 upper inversion was reached at an altitude as low as 9,328 meters 

 (5.8 miles) on the front of an anticyclone. It was also reached at the 

 low elevation of 9,712 meters (6 miles) in the transition region 

 between a cyclone and an anticyclone, and at an altitude of 9,372 

 motors (5.8 miles) in a cyclone, while on other occasions in cyclones it 

 has been reached at altitudes ranging from 10,000 to 14,000 meters 

 (6 to 8.7 miles). The greatest altitude at which it was encountered, 

 14,983 meters (9.3 miles), on September 28, 1909, was not in an 

 anticyclone, but in the transition region between a northern cyclone 

 and a southern anticyclone. 



In the United States the seasonal distribution of the ascensions 

 has not been so good as might be wished. If the year bo divided into 

 two portions, the warmer half, or from April to October, inclusive, 

 and the colder half, from November to March, inclusive, the following 

 results are obtained for the average height of the lower limit of the 

 upper inversion : 



Meters. 



Rotch, warmer half, 19 ascensions 11, 986 



Weather Bureau, warmer half, 29 ascensions 11, 308 



Rotch, colder half, 5 ascensions 11, 192 



Weaiher Bureau, colder half, 21 ascensions 11, 082 



Thus it is seen that the lower limit of the upper inversion in the 

 United States is found at a slightly less altitude in winter tlian in 

 summer, agreeing in the main with Euro})ean observations. The 

 winter series of 21 ascensions w^as made from February 8 to March 4, 

 inclusive. The summer series was made mostly in September and 

 October. 



By reason of tho clear sides and relative^ dry air of South Dakota 

 and other western States it was possible to make observations on the 

 motions of the balloons after they had gotten well into the region of 

 the upper inversion, and thus to obtain some interesting facts con- 



