160 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



however, there is fau" ngrcement between surface pressures and upper 

 wind (h-ift. In pjeneral tliere is a northerly component in the winds in 

 front and on tiie east side of an anticyclone, although numerous 

 excei)ti()ns to this rule have been noted. One of the most marked 

 exceptions was on November 25, 1904, when a balloon launched at 

 St. Louis, Mo., traveled almost due east to near Louisville, Ky., 

 although the pressure distribution at the surface clearly indicated 

 northerly winds, and winds from that direction actually prevailed at 

 the ground. This balloon, which reached an altitude of 11,500 

 meters (7.1 miles), and the one sent u]) the following day, moved with 

 the enormous average velocity of 100 miles per hour. The second 

 balloon, instead of moving toward the east, as did the one launched on 

 the previous day, moved in a south-southeast direction and landed in 

 western Tennessee. From tliis change in direction of the air cur- 

 rents it is evident that some temporary disturbance occurred in the 

 atmosphere sufficient to modify gi-eatly the eastward flow. What the 

 disturbance was is not apparent from surface conditions. On the day 

 that the balloon moved eastward there was a marked barometric 

 depression over southern New England which had been stationary for 

 about 24 hours. It may have been that the pressure in the higher 

 levels over New England was falling on the day in question, and that 

 the high eastward velocities encountered by the balloon were due to a 

 pressure gradient that existed in the upper regions only. Harm 

 showed more than 20 years ago that atmospheric pressure on moun- 

 tain tops continues to fall for some time after the turn to rising 

 pressure has set in over surrounding low levels. 



The cause of the changes in the direction of the wind aloft is not 

 always apparent from surface distribution of temperature and pres- 

 sure. Primarily, the direction of the wind on the earth's surface is 

 dependent on the temperature and pressure, the winds blowing from 

 regions of low to regions of high temperature and from regions of 

 high to regions of low pressure. In the United States the strong 

 winds of winter have regions of higher temperature on their right 

 and in slightly higher latitudes. Unfortunately we are not able to 

 study the temperature changes in the atmosphere as a whole, but 

 only in a thin stratum next to the earth's surface. The upper winds 

 in the United States are uniformly from the west, as has been fully 

 demonstrated in the past. That these prevailing westerly winds 

 are subject to important modifications is shown by the motion of 

 the upper clouds and by the travel of sounding balloons. 



Sounding-balloon ascensions have added very much to our knowl- 

 edge of the temperature of the atmosphere up to heights of 15,000 

 meters (9.3 miles) and even higher, but the number of ascensions to 

 heights above 9.3 miles is as yet small. 



The vortical distribution of temperature in diiTcrent sections of the 

 same anticyclone is well shown by the simultaneous ascensions at 

 Omaha, Nebr., and Indianapolis, Ind., on October 5, 1909. The two 

 stations were, roughly speaking, within the influence of a great anti- 

 cyclone, Indianapolis being nearest the center and under the higher 

 pressure. The pressure at Indianapolis being higher than that at 

 Omaha, we should expect lower surface temperature, as was actually 

 found. But the low temperature of the air column over Indianapolis 

 extended up to 2 km. (1.2 miles) only, at which level the air-column 

 temperatures at the two places were reversed, the western station 



