WEATHER BUREAU. 161 



becoming the colder at that level, and steadily remaining so up to 14 

 km. (8.7 miles). During an earlier ascension at the two stations, on 

 September 30, 1909, the surface weather conditions were qhite 

 different from those of October 5, the two stations being separated 

 by a shallow anticyclone, with Indianapolis on the eastern edge and 

 Omaha on the western edge. As in the first-named case, 'the eastern 

 station was the colder up to about 3 km. (1.9 miles), but from that 

 altitude up to about 12 km. (7.5 miles) the Omaha air column was the 

 colder, the difl'erence at the 12 km. level amounting to 16° C. (28.8° F). 

 Marked variations of the temperature at similar great altitudes have 

 been recorded elsewhere, especially in England, where the tempera- 

 ture of the lower limit of the upper inversion has been found to dift'er 

 on the same day as much as 20° C. (36° F.) at stations not more than 

 150 miles apart. The lowest temperature recorded in any of the 

 Weather Bureau series of ascensions was —68.9° C. ( — 92° F.) at 

 Huron, S. Dak., in September, 1910. 



A study of observations at mountain stations in Colorado has shown 

 that variations of temperature at the summit and at the base stations 

 are nearly coincident in point of time and are generally similarly 

 directed, but that there are occasions when a fall in temperature sets 

 in on the plains while the temperature on the mountain tops is still 

 rising. In rare cases, also, the weather conditions on the mountain 

 summits are controlled by causes that are not operative on the plains 

 to the eastward. These studies have increased our knowledge of the 

 effect of local topography in the warming and cooling of the air that is 

 trapped between the mountain ranges. The important fact, revealed 

 in connection with sounding-balloon ascensions, that the prevailing 

 eastward drift of the atmosphere is wholly suspended during the 

 prevalence of strong anticyclones is coniirnied by a study of the 

 records of wind movement over the high stations of eastern Colo- 

 rado at Corona and Pikes Peak. There can be no doubt that the 

 local circulation in strong anticyclones up to the level of Pikes Peak is 

 controlled by the anticyclone, though this is seemingly controverted 

 by observations on the movement of high clouds in other parts of the 

 United States. 



The cirrus level in the United wStates is about 15 km. (9.3 miles) 

 above sea level. Clouds in this level have been observed to move 

 directly across the central areas of anticyclones, from w«st to east, 

 which movement would not be possible did an easterly current 

 prevail at that level. The wind movement over Pikes Peak, Colo., 

 4,301 meters (14,111 feet) above sea level, is from the northeast when 

 an anticyclone occupies the Great Basin to the westward, thus indi- 

 cating the local control of the wind circulation by anticyclones at the 

 level of Pikes Peak. 



At Mount Weather, Va., the kite flights thus far made show that 

 practically all easterly winds, except under special conditions, are 

 shallow winds; that is, they are generally less than a mile in vertical 

 extent. 



SOLAR RADIATION. 



Between July 16 and October 10, 1910, Prof. Kimball was engaged 

 in a pyrheliometric survey of the region west of the Great Lakes and 

 the Mississippi River, preliminary to the establishment of permanent 



23165°— AGB 1911 11 



