PHYSICAL OOEANOGEAPHY OF THE GULF OF MAINE 



841 



Evaporation, of course, partially offsets precipitation. Unfortunately, no data 

 are available on this subject from any localities that might be supposed to approxi- 

 mate conditions as they prevail at sea in the Gulf of Maine; the outer islands, for 

 example, would be such. Nevertheless, there is no reason to suppose that evapora- 

 tion at sea is greater than on land, especially when the sea is blanketed with thick 

 fog, as the northern and northeastern parts of the gulf and its offshore banks often 

 are during the summer season. The following records of evaporation for Maine, 

 Massachusetts, and Nova Scotia may therefore be taken as the maximum. The 

 average monthly evaporation from a free water surface at three stations in Maine 

 in the basins of the Penobscot, Kennebec, and Androscoggin Rivers is given by 

 Barrows (1907a, p. 114) as follows, in inches: 



Month 



March. 

 April .- 

 May--- 

 June--- 



Average 

 evapora- 

 tion, in 

 inches 



2.23 

 3.48 

 1.90 

 2.87 



July 



August 



September . 

 October 



Month 



Average 

 evapora- 

 tion, in 

 inches 



5.28 

 6.12 

 3.00 

 2.33 



No data are available for the winter months, when the observations were neces- 

 sarily made from a frozen surface, but it may be assumed that evaporation takes 

 place no more rapidly from open water from November through February than in 

 October or March — say at the rate of about 2.2 inches monthly. This suggests a total 

 evaporation for the year of about 35 inches of fresh water." According to F tz- 

 Gerald (1886), the annual evaporation is somewhat larger near Boston (about 39 

 inches), as might be expected. 



Data supplied by the United States Weather Bureau for Yarmouth, Nova 

 Scotia, more closely paralleling conditions over the gulf because of the greater fre- 

 quence there of onshore winds, show the following monthly averages over a period 

 of 13 years: 



Evaporation at Yarmouth, Nova Scotia 



Month 



April 1 

 May - 

 June - 

 July- 



Average 

 evapora- 

 tion, in 

 inclies 



1.08 

 3.04 

 3.49 

 3.94 



Month 



August 



September . 

 October 



Average 

 evapora- 

 tion, in 

 inches 



3.65 

 3.67 

 1.69 



' 1920 only; ice in the tank on several days. 



Assuming an average evaporation of 1.5 to 2 inches monthly, for the period 

 November to March, the annual evaporation of fresh water at Yarmouth would be 

 close to 29 inches from a surface of open (not frozen) water; the average for the Gulf 

 of Maine is probably not more than 30 inches. These measurements are for fresh 



"These measurements were taken freely exposed to the sky (Barrows, 1907a, p. Ill, pi. 21). 



