Chesapeake Li/^htship 



Winter surface temperatures tended to be several der,rees 

 lower than tho 19U7-1956 mean. The spring warm.-ins lagged behind the 

 mean. Summer surface temperatures tended higher than the mean except 

 for a depression in mid— July. Autumnal cooling preceeded the mean ex- 

 cept for a sudden retardation of cooling in December. 



Minimum temperatures, less than 38'-'F, occurred during the 

 last-third of January. During February and March surface temperatures 

 were usually only a fraction of a degree warmer than the bottom tempera- 

 tures at the surface of greater than 77°F were reached in mid-August. 

 Maidnum temoeratures at the bottom of greater than 72°F were reached in 

 mid-September at the commencement of the autumnal overturn. 



Surface salinity ranged from 32 /oo at the beginning of the 

 year to less than 26°/oo in late June followed b^^ an irregular recovery 

 to 32°/oo at year end. Bottom salinities tended to be several parts 

 per thousand -lore saline during most of the year, but during the period 

 of marked turnover in the water column surface and bottom salinities 

 were nearly identical. 



The depression in surface temperature in mid-July resulted 

 from an intrusion of cold saline water from offshore which influenced 

 the whole water column. The intrusion appears to follow a period of 

 preponderant strong southerly w?nds. The winds observed at the light- 

 ship vrere predominantly strong southerly for the first two thirds of 

 July end averaged to very light westerlies during the third-ttiird when 

 the deeper water became much warmer. Inasmuch as the mean surface pres- 

 sure map for the month of July 19% is almost an exact replica of the 

 long-time normal it may be that the condi.tion which produced the en- 

 croachment of cold water is a normal phenomenon. V/e have no previous 

 data on this subject other than the daily surface water temperature 

 records for previous years. The one-third monthly means for previous 

 years indicate a tendency for a surface water temperature depression 

 at some tiie during the sujnmer. This was particularly marked in 19pU 

 when the usual maximum surface te-aperatures were not reached. 



Comparison of the day to day fluctuations in the temperature 

 at all depths during the summer of 1956 Trith the wind systems indicated, 

 in general, that colder temperatures at the middle and lower depths are 

 associated with southwesterly winds, while warming occurs with north 

 easterly or easterly wi.nds. Presumably the strong southwesterly and 

 westerly winds move the surface water offshore and allow the encroachment 

 of colder more saline water ''rem offshore. NortVeasterly and eastei'ly 

 winds on the other hand press the coastal water against the shore and 

 force the deeper water off shore. This is similar to the phenomenon 

 reported hy Longard and Banks (19^2) at Sambro Lightship but requires 

 less wind for a shorter duration. Here we have only a two layered sys- 

 tem whereas they had a three layered system. 



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