INTRODUCTION 



Environmental forecasting techniques for predicting near-sur- 

 face thermal structure have been developed under the Antisubmarine 

 Warfare Environmental Prediction Services (ASWEPS) program for deep- 

 water areas seaward of the Continental Shelf, Extension of ASWEPS 

 forecasts into the relatively shallow water over the Continental 

 Shelf is now under development. The complex oceanographic environ- 

 ment of shallow-water areas may require modification of present 

 techniques. As an initial step toward developing shallow-water 

 prediction techniques, a program has been initiated to investigate 

 the thermohaline structure in selected areas inshore of the 500- 

 fathom (914 meters) isobath. Collected data will be used to deter- 

 mine the nature, frequency, and extent of changes in the thermo- 

 haline structure. 



The initial survey, designed to investigate the thermohaline 

 structure during winter in the area seaward of the Virginia Capes, 

 was conducted from 24 to 26 February and from 8 to 11 March 1967. 

 A second survey, designed to investigate the thermohaline structure 

 during late summer, was conducted from 19 to 22 September and from 

 6 to 13 October 1967 and will be the subject of a future report. A 

 third survey, designed to investigate the thermohaline structure 

 during spring, is scheduled for May 1969. The two periods of the 

 initial survey are hereafter referred to as Phase I and Phase II. 

 Locations of the stations taken during each phase are shown in 

 figures 1 and 2, 



BACKGROUND 



A comprehensive study by Bigelow (1933) of the thermal struc- 

 ture over the shelf between Cape Cod and Cape Hatteras shows that 

 during winter (1) minimum water temperature occurs late in February 

 or early in March, (2) isotherms are oriented parallel to the coast 

 with lowest sea surface temperatures (SST) observed inshore, (3) 

 the vertical temperature profile generally is either isothermal or 

 increases slightly with depth, (4) little or no vertical stability 

 occurs with the result that heat gained through solar radiation is 

 rapidly mixed downward, and (5) advection of water from other sources 

 may cause complex thermal conditions. 



Bigelow and Sears (1935), in a study of salinity distribution 

 over the shelf, state that (1) isohalines generally parallel the 

 coast with a gradual transition from low inshore values to high off- 

 shore values, (2) minimum surface salinity occurs during late winter, 



(3) the vertical water column may be nearly isohaline during winter, 



(4) complex salinity gradients near the Continental Slope may result 



