CLIMATIC FACTORS : RADIANT ENERGY 



123 



day night day night day night 



Time of Readings 



day 



NIGHT 



DAY 



FlG. 64. Maximum day and night soil temperatures taken on a sand dune 

 at Beaufort, N. C. in August, 1947. Readings were made on successive days 

 at 7:00 A.M. and 7:00 P.M. for night and day maxima, respectively. Tempera- 

 tures were greatest at the soil surface and were successively less with increas- 

 ing depth by day, but, at all depths at night, dropped as low, or lower than 

 the maximum at eighteen inches. Minimum temperatures fluctuated within 

 the range of 72-85° F. (difficult to show accurately on so small a scale). At 

 eighteen inches the minimum was never more than, one degree below the 

 maximum, but the difference between minimum and maximum increased up- 

 ward to the surface where one minimum was as low as 72° F. 



bodies of water are slower to warm up and slower to cool than 

 land because of the higher specific heat of water. In addition, they 

 reflect much of the insolation, and what heat is absorbed is dis- 

 tributed to much greater depths by water motion and convectional 

 currents. As a result, temperature extremes are reduced around 

 bodies of water as compared to those inland. The effect on plant 

 distribution is particularly evident in the ranges of southeastern 

 species, which often extend to the northern limits of the Atlantic 

 coastal plain, where, undoubtedly, they are able to survive because 

 of the maritime climate. The amelioration of temperatures is ap- 

 parent about lakes as well as oceans, although to a lesser extent. 

 The extremes of winter and summer temperature characteristic of 

 the Dakotas are never experienced in lake-bounded Michigan, al- 

 though latitudes are essentially the same. 



