COLD AIR DRAINAGE 



FORREST SHREVE 

 The Desert Laboratory, Tucson, Arizona 



The arid regions of the earth exhibit great daily ranges of tem- 

 perature by reason of conditions which permit a rapid heating 

 of the soil by day and a correspondingly rapid cooling through 

 radiation at night. The chief conditions which permit these rapid 

 changes are the absence of a heavy plant cover, the predominance 

 of sands and stones, and the usual absence of a nocturnal cloud 

 blanket. The rapidity of nocturnal radiation in the desert is 

 responsible for the phenomenon known as inversion of temperature, 

 which is at once a cause and an effect of cold air drainage. Inver- 

 sions of temperature in the free air have been made known through 

 observations on the Eiffel Tower in Paris and through kite obser- 

 vations at the Blue Hill Observatory. They have also been 

 observed in mountain valleys, particularly in the Alps. Their 

 importance to vegetation was first pointed out by Kerner, 1 and 

 their pronounced character in arid regions as related to vegetation 

 was first remarked by MacDougal 2 for the vicinity of Flagstaff, 

 Arizona. Any thermometrical instrumentation carried out in the 

 desert must be made with strict heed to the local conditions of 

 cold air drainage, and the comparison of nocturnal or minimum 

 temperatures from several stations must be made with a full 

 knowledge of their topographic site. 



During the past year the writer has been attempting, in con- 

 nection with other instrumentation, to determine the normal 



1 Kerner, A., Die Entstehung relative hohen Lufttemperaturen in der Mittelhohe 

 der Thalbecken der Alpen im Spatherbste und Winter. Zeitschr. f. Meteorol., 

 11: 1-13, 1876. 



2 MacDougal, D. T., Influence of inversions of temperature, ascending and de- 

 scending currents of air, upon distribution. Biol. Lectures, Mar. Biol. Lab., 

 Woods Holl, 1899. Boston, 1900. 



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