668 BULLETIN OF THE BUEEAU OP FISHERIES 



RELATIONSHIP BETWEEN THE TEMPERATURE OF THE SURFACE 



AND OF THE AIR 



The daily air and surface temperatures for Gloucester, Boothbay, and Lubec for 

 the year 1919-20 (figs. 29 to 31) show the air constantly warmer than the water 

 along the western and northern shores of the gulf from the middle of that March 

 until late in October, a difference averaging greatest from some time in June until 

 the last half of August. During the summer the 10-day averages for air and water 

 frequently differ by 4° C. — occasionally by as much as 7° — and very hot days would 

 show a still wider divergence. 



The 10-day averages for air and water recorded by Eathbun (1887) for the 

 years 1881 to 1885 are of the same tenure at the following Hghthouses: Thatchers 

 Island, Boon Island, Seguin Island, Matinicus Rock, Mount Desert Rock, and 

 Petit Manan, with air averaging warmer than water after the first half of March. 

 At Eastport, too, the Signal Service of the United States Army found the mean tem- 

 perature of the air higher than that of the water after March 21 for the 10-year 

 period, 1878 to 1887 (Moore, 1898, p. 409). 



In 1920 the Albatross '^^ foimd the air averaging about 1.7° colder than the water 

 across Georges Bank during the night of February 22-23 and up to 1 p. m. of Febru- 

 ary 23, but the average difference between air and water was only 0.7° (day and 

 night) on the run in from the bank to Massachusetts Bay on that date, with air and 

 water temperatures precisely alike in Massachusetts Bay. 



On March 2 to 4 (stations 10252 to 10260) in that year the surface of the cen- 

 tral parts of the gulf (stations 20052, 20053, and 20054) still continued warmer than 

 the air up to March 2 to 4 (average difference about 1.5° C.) ; but the air had warmed 

 so fast over the land that the air readings for the coastal sector between Penobscot 

 Bay and the inner part of Massachusetts Bay (stations 20055 to 20062) were con- 

 sistently 1.1° to 5.6° higher than the surface readings by that date, night as well as 

 day, averaging about 3.5° warmer. 



This regional difference between the coastwise belt and the water farther out at 

 sea had disappeared by the 10th to 11th of March, when the Albatross ran out from 

 Boston to the southeastern part of the basin (station 20064), the air now being con- 

 stantly warmer than the surface over the 24-hour period, 1 p. m. to 1 p. m. From 

 that date on the hourly readings showed the air invariably warmer than the water, 

 except on March 20, when we ran along the west coast of Nova Scotia to St. Marys 

 Bay in a southeast storm with snow squalls. 



Apart, then, from extremes of weather, the air averages warmer than the surface 

 of the gulf from about March 10 on, though the precise date when this state is estab- 

 lished varies from year to j'^ear and falls a week or more sooner near land than out 

 in the central parts of the gulf. 



"Hourly temperatures, United States Bureau of Fisheries (1921, p. 183). 



