64 Lloyd and Tracy : The insular Flora 



Sunshine 



The data available are those based upon six years' observation. 

 These show that the average number of cloudless days per annum 

 in this region is 154 against 141 at Hatteras, while the average 

 number of totally cloudy days for the two places is very nearly 

 the same. The average total number of partly cloudy days is ac- 

 cordingly less for the Delta region (1 17 to 130) giving that region 

 an amount of sunshine greater by about 2 1 days. This and the 

 lower relative humidity of the atmosphere, indicate an amount of 

 energy available in the form of light considerably greater than at 

 the more northern station, namely Ocracoke. 



Wind 



The average velocity of the wind is very near to 13.2 kilometers 

 (8.2 miles) (Hatteras, 2 1.4 kilometers (13.3 miles)) and the total wind 

 movement per annum, 1 18740.3 kilometers (73,619 miles) as com- 

 pared with a wind movement of 191,935.5 kilometers ( 1 19,000 

 miles) at Hatteras.* The total wind force is therefore small. The 

 prevailing direction of the wind is southeast. The total wind move- 

 ments, however, from the south points of the compass exceed those 

 from the north points by only a little, and are to each other in the 

 ratio of 10 to 8. This fairly equal distribution of winds about the 

 points of the compass accounts for the absence, for the most part, 

 of those asymmetrical growth forms which are referred to the me- 

 chanical action of the wind. The direction of the wind in summer 

 months is almost constantly southeast and the small amount of 

 distorted growth is due to this fact as the direction which that 

 growth takes indicates. 



Summing up the above data the climate of the delta region 

 may briefly be described as having : ( 1) A very long growing season, 

 as shown by the sudden rise of the curve in the accompanying 

 figure (Fig. 1), after the middle of January ; (2) A large amount of 

 precipitation well distributed throughout the year; (3) A high 

 relative humidity with little annual variation ; (4) A high degree 

 of insolation, the effect of which is somewhat lessened by the high 

 relative humidity, and (5) A relatively small wind force well dis- 



■ <^— , ^ — ^-^-_^ 



* Based on six years' observations. 



