56 BULLETIN 1233, U. S. DEPARTMENT OF AGRICULTURE. 



It is, perhaps, of first importance to note that the total wind move- 

 ment by years varies only within somewhat narrow limits. For the 

 seven years for which there arc almost complete records the mean 

 variation from normal is only 3.7 per cent of the total movement, 

 while the Colorado Springs station shows an average variation of 5.1 

 per cent during the eight years 1910 to 1917, inclusive. The varia- 

 tion between growing seasons is even less important. For the 11 

 complete growing seasons the local station shows an average varia- 

 tion of 2.7 per cent of the total movement, while Colorado Springs 

 for eight years shows an average variation of 7.5 per cent, the growing 

 season on the plains being thus more variable than the year as a 

 whole. The similarity of different growing seasons speaks for the 

 importance and stability of the mountain and valley breezes, as well 

 as for the practical immunity of the station to cyclonic influences 

 which express themselves during the summer in the form of southerly 

 winds. Apparently the least variation is to be expected in the last 

 decade of June, when the influence of insolation is probably the 

 greatest. 



It is noted that the period of greatest calm, when the wind drops 

 to an average velocity of 4.1 miles per hour, is at the middle of August, 

 which also represents the climax of the summer rainy period, or at 

 least a period when rains seldom fail. The cloudiness at this season 

 reacts, of course, to retard the conventional flow of the mountain and 

 valley breezes, while the cumulative effects of summer temperatures 

 have doubtless at this time brought about the nearest approach to 

 equilibrium of mountain and valley radiation. 



From the middle of August to the end of the year the wind veloci- 

 ties gradually increase without important variation, and the maxi- 

 mum velocities are recorded during the second decade of January. 

 This must be related to the general cosmic conditions. These are 

 "anticyclonic" winds, blowing toward the centers of low-pressure 

 areas, which during the winter almost invariably take a route across 

 the southern portion of the United States. Anticyclonic winds are 

 generally more violent than those in advance of the storm area, and 

 only the anticyclones are of importance at the control station, because 

 cyclonic winds during the winter season are locally opposed to pre- 

 vailing mountain breezes, which result from higher temperatures on 

 the plains. 



Further evidence of the character of the winter winds at Fremont 

 is found in the fact that they sutler a decline during February and are 

 again important in March. In other words, they reach, locally, their 

 greatest strength just before and jus( after the cyclonic storms have 

 reached their southernmost course, which is normally in February. 

 And they are probably less violent winds in February than in Janu- 

 ary or Maceli, because the storm centers are farthest away in Feb- 

 ruary. Their more northerly origin in February might be thought 

 to aneel their local force at the control station, but when other sta- 

 tions show the same feature this point loses significance. 



The important biological fact is, then, that the winds coming during 

 the coldest part of the winter, when practically all mountain soils are 

 frozen, are most violent and incessant of any during the whole year, 

 are dvy because they are anticyclonic, and are of an especially injii- 



