Table 6. Mean monthly relative humidities (%) for OIOO, 0700, 1300, 1900 



hours, and 24 hour average from south Florida first order weather 

 stations (adapted from USDC 1981a, 1981b, 1981c). 



typically on the order of 75% to 

 90%, and generally lowest in the 

 afternoon hours, averaging from 50% 

 to 70%. On a seasonal basis, mean 

 relative humidities tend to be 

 lowest in the spring months (April) 

 and highest in the summer and fall 

 months, although seasonal differ- 

 ences are not great. The Florida 

 Keys, reflecting a dominant maritime 

 influence, show even less daily and 

 seasonal variation. Also, the sea- 

 sonal peak for the Keys appears more 

 in the fall as opposed to the summer 

 as observed in Miami (USDC 1981a, 

 1981b). Figure 16 illustrates the 

 more stable relative humidity exhib- 

 ited in the Keys compared to main- 

 land stations. 



3.6 SOLAR RADIATION 



Throughout the year, incoming 

 solar radiation varies little within 

 the latitudinal constraints of the 



Everglades/Bay/Keys basin (Dames 

 and Moore 1978). What does vary 

 are factors such as cloud cover, air 

 pollution (particulate load or dust- 

 iness), and relative humidity, which 

 modify the transmission, absorption 

 and reflection of solar energy 

 .(Blair and Fite 1965, Bamburg 1980). 

 These factors result in temporal and 

 spatial variations in the amount of 

 solar radiation reaching the land 

 and water surfaces. 



Miami is the only first-order 

 weather station to collect solar 

 radiation data in or near the study 

 area (Bradley 1972). From 20 years 

 of records, the average daily solar 

 radiation reported is 447 langleys 

 (gm-cal/cm^) . Monthly variation 

 ranges from 319 langleys in December 

 to 572 langleys in April (Bradley 

 1972). The higher values are re- 

 ported during middle to late spring 

 rather than during the summer 



36 



