CORRELATION OF DISTRIBUTIONAL FEATURES. 



525 



the temperatures of the coldest periods of winter assume on passing 

 to a warm subtropical zone in which there are no cold days in our sense. 

 The number of days in the longest normal rainy period of the frostless 

 season appears to be of narrow amplitude in the Lower Sonoran Zone, 

 although this is not accurately determinable. Its values and ampli- 

 tudes are doubtless very similar to those of the Upper Sonoran Zone, 

 as indicated by a comparison of figure 39 and figure 41. While, in 

 other words, there is a sharp contrast between the conditions in the 

 Upper and Lower Sonoran Zones with respect to one of the most 

 critical temperature conditions of the latter, there is a similarity with 

 respect to a moisture condition which is not critical in separating these 

 zones, but is critical in separating them from their eastern humid 

 analogues. The moisture ratios, which show narrow amplitudes for 

 this zone, are also very similar in range and amplitude to the moisture 

 ratios of the Upper Sonoran Zone. 



Austroriparian Zone (fig. 42). — The temperature conditions of this 

 zone show less similarity to those of the Lower Sonoran Zone than is 

 shown by a comparison of Upper Sonoran with Carolinian or Transi- 

 tion with Alleghenian. The amplitude of the length of the frostless 

 season is relatively narrow, and that of all the other temperature con- 

 ditions is narrower than in the Lower Sonoran. There are rather wide 

 limits, however, within which the temperature conditions of these two 

 zones overlap. 



The normal daily mean precipitation ranges through a wide ampli- 

 tude in the Austroriparian Zone, exceeding its ampUtude in the Caro- 

 linian. The number of days in the longest normal rainy period of the 

 frostless season also reaches much higher maximum values in the 

 former zone than in the latter. With these exceptions, there is a general 



' TCMrHMTURC 



D>v« IN Normal FrostlcM Simon F. S.) 



Hot Days, T. S. 



Cold Days, F. S. 



Physiolosical Summation. F. S. 



Normal Daily Mcan, coldest 14 days or YcAR 



Normal Daily Mcan, Vcar 



PRtCIRITATION 



Normal Daily Mean, F. S. 

 Days in lonsist Normal Rainy Period. F. S. 

 Days in longest Normal Dry Period, F. S. 

 Mean Total. Year 



Evaporation 

 Daily Mean. iee7>6, F. S. 



Moisture Ratios 

 Normal P/E, F. S. 

 Normal (t/E, F. S. 

 Normal P/E, Year 



Humidity 

 Normal Mean. F. S. 



Sunshine 

 Normal Daily Duration. F. S. 



Moisture-Temperature Indices 

 Normal P/E x T. F. S., Physiological Method 



Fig. 42. Climati 



UH 



c extremes for the Austroriparian Zone. 



