524 CORRELATION OF DISTRIBUTIONAL FEATURES. 



determined, amplitude for the Carolinian, and the length of the dry- 

 period shows an even greater, but also inaccurately determined, ampli- 

 tude for the Upper Sonoran. 



The moisture ratios show higher values and wider amplitudes for the 

 Carolinian than for the Upper Sonoran, as was true of their more 

 northern analogues, the indication being that the conditions expressed 

 by these ratios are somewhat less critical in the moister Carolinian 

 Zone than in the Lower Sonoran. 



Lower Sonoran Zone (fig. 41). — When a conlparison is made between 

 the zones which form the eastern and western halves of a given region, 

 the temperature conditions are found to be similar in the two and the 

 moisture conditions dissimilar. When a comparison is made between 

 the temperature conditions of the Upper Sonoran and Lower Sonoran 

 Zones, the values and amplitudes are found to be dissimilar, whereas 

 the moisture conditions in the two are very much alike throughout, 

 with the exception of the higher range of evaporation in the Upper 

 Sonoran. 



The length of frostless season in the Lower Sonoran ranges from 

 106 to 331 days, which is both a wider amplitude and a higher series 

 of values than those found in the Upper Sonoran. Other very wide 

 amplitudes are those of the normal daily mean temperature for the 

 year, the number of days in the longest normal dry period within the 

 frostless season, and the daily mean evaporation for the frostless 

 season. These are all conditions which are likewise of wide amplitude 

 in the Desert region. 



One of the narrowest amplitudes of this zone is the normal daily 

 mean for the coldest 14 days of the year, for which the amplitude in 

 the Upper Sonoran is great. This emphasizes the importance which 



TCMPERATURC 



Days m Normal Frobtlcss Scason (F. S.) I "~^^^B^BMMm^^M*8M^iWWH^BiWBMBmiM!^IIZII] 



Hot Days, F. S. L_ 



Colo Days. F. S. [I 



Physiological Summation, F. S. 

 Normal Daily Mean, coldest 14 days or Year [ 

 Normal Daily Mean. Year 



Precipitation 

 Normal Daily Mean. F. S. 



Days in longest Normal Rainy Period. F. S. [ 

 Days in longest Normal Dry Period, F. S. 

 Mean Total, Year 



Evaporation 

 Daily Mean. 1687-8, F. S. [ 



Moisture Ratios 

 Normal P/E. F. S. 

 Normal n/Z, F. S. 

 Normal P/E. Year 



Humidity 

 Normal Mean. F. S. C 



Sunshine 

 Normal Daily Duration. F. S. C 



Moisture-Temperature Indices 

 Normal P/Z x T. F. S., Physiological Mcthoo I 



Fia. 41. Climatic extremes for the Lower Sonoran Zone. 



