TM No. 377 



located in the range of periods of 10-1,5 minutes and less, "these fluctuations 

 or pulsations must "be taken into account in. the records of wave motions made 

 ever these suggested time periods , 



Since the gross tidal currents are relatively predictable at the BBELS,, 

 a closer examination of them should reveal the causes of anomalies in the 

 tidal pattern; i..e<,^ the effects of wind upon the predominantly x-idal and in~ 

 temal flow. Indeed., the BBELS facility could be of great use in the study 

 of infra -tidal freqiaency motions „ 



Temperature Data ~- The seasonal variation in the thermal structure ex- 

 hibited in the vicinity of the BBELS is typical for a coastal region in the 

 temperate zone* There are quite strong annual variations of water temperature 

 caused by the interaction of the seasonably variable continental shelf water 

 with the fresh water runoff from various rivers and bays north of the light 

 station along the Massachusetts and Rhode Island coast (see figure IV-3)* A 

 data report on the seasonal distribution of oceancgraphic variables in Phcde 

 Island Sound (which includes the location of BBELS ) has been prepared by 

 Shonting,, Cook, , and Wyatt (1966). 



A gross picture of the tnermal structure was obtained by making bathy- 

 thermograph lowerings from the BBELS prior to each of the later series of 

 wave measurements (BBELS numbers ll-l6). A composite plot of the temperature 

 profiles (figure IVX12) shows that Isothermal conditions exist during the 

 winter months., whereas the water tends to stratify during the late spring 

 and summer „ (The salinity stratification in the vertical is generally not 

 intense enough to affect 1he stability of the water column in the region of 

 BBELS.) The currents from Buzzards Bay and Vineyard Sound, mixing with the 

 waters of Rhode Island Sound, apparently suppress temperature stratification 

 in the region of the light station e Further westward,, toward Block Island., 

 much more intense stratification exists during the late spring and summer 

 months (see Shonting and Cook,, 1967). 



Some seasonal surface temperatures for the BBELS location are shown in 

 figure IV-13o The circles are taken from a monthly aei ial survey (using an 

 infra-red radiation thermometer) made during l$6h by the Sandy Hook Marine 

 Laboratory and the Coast Guard under contract with NUW5 U Due to inherent 

 problems associated with this method (see Clark., 1964) ,, the values are probably 

 only reliable to within + Io5°C<. Also,, they do not accurately represent the 

 water temperature a few centimeters below the ocean surface.: The crosses in 

 figure IV-13 indicate the surface temperature registered by bathythermograph 

 observations taken at BBELS.- The seasonal range of temperature is roughly 

 l8-19°Co Tne minimum value occurs in late January, and the maximum in August e 



Wind Measurements -- Observations of wind speed and direction were made 

 aboard the BBELS during periods of wave measurements a During the first few 

 series of wave observations^ wind speed and direction readings were usually 

 taken once or twice per hour* It was found from experience that;, because of 

 the relatively high variability In both the wind speed and direction, it was 



85 



