IMPORTANT WINDS. 9 



The work of Prof. King, 1 in determining the effect of a windbreak 

 upon the evaporative power of the wind, and that of Prof. Card, 2 in 

 evaporation, measurement of soil moisture, and effect of windbreak 

 protection on a crop of millet, have been highly suggestive in carrying 

 out the study. 



Since the need for windbreaks on the treeless plains of the Middle 

 West is exceptionally great, and since a large number of windbreaks 

 are there available for study within a comparatively small area, the 

 States of Kansas and Nebraska were chosen as the chief field, though 

 studies were carried on in southern Minnesota and in Iowa as well. 

 The results were obtained in a plains country, in which differences of 

 topography do not figure prominently. The necessity of eliminating 

 from the experiments the factors of slope and aspect will be plainly 

 seen in the following discussions. 



^/IMPORTANT WINDS OF THE UNITED STATES. 



There is scarcely any part of the United States which is not swept 

 by winds capable of doing serious injury to homes, cattle, orchards, 

 or fields. The winds which do the greatest damage and from which 

 protection is needed are (see diagram 1): 



(1) The sea breezes of the Atlantic coast and of the Great Lakes. 

 These may throw up sand dunes along the coast and affect orchards 

 and tender crops by reducing temperatures. They are sometimes 

 augmented by coastal winds resulting from West Indian storms. 



(2) The anticyclonic, dry winds of the upper Mississippi Valley and 

 the western Lake region, which, especially in the spring and early sum- 

 mer, often blow steadily from the west or southwest for several days. 



(3) Anticyclonic winds of the central and southern portion of the 

 Mississippi Valley, usually from the southwest, but more or less 

 influenced in summer by the general continental winds from the 

 southeast and in winter by winds from the north. These also are 

 often very persistent in summer and are exceedingly dry when blow- 

 ing off the plains of the Southwest. The northwest winter winds of 

 the entire Mississippi Valley are usually very cold and dry, and are 

 likely to injure vegetation. 



(4) The Chinook, which blows out of the northern Rocky Moun- 

 tains, increasing in warmth and dryness with its descent, and, in the 

 Canadian Provinces, Montana, and the Dakotas, doing great damage 

 by prematurely accelerating plant growth, which later may be sub- 

 jected to extreme cold. 



(5) The Santa Ana, or desiccating north wind of southern Cali- 

 fornia, which blows from the Mohave Desert, and similar winds on 

 the coasts of Washington and Oregon which blow from the high 

 plains, are often destructive to vegetation by reason of their dryness. 



i Bull. 42, Wis. Agr. Exp. Sta. Bull. 48, Nebr. Agr. Exp. Sta. 



