INTRODUCTION 



The ASWEPS research program being conducted at the Bydrographic Of- 

 fice* includes a systeniatic investigation of the physical processes in- 

 volved in the daily heating cycle of the upper layers of the ocean. This 

 investigation is being conducted in order to determine the effect of 

 these processes on the thermal structure and to devise an analytical 

 short-range prediction technique. The approach follovs the method out- 

 lined by Schule (1952). A thermal structure prediction program based on 

 meteorological parameters has been tested by this office (Nix I962). 

 This report summarizes the results of an attempt to find the numerical 

 values of some vertical physical processes in the water under conditions 

 of minimal horizontal variations. 



tfeny studies of diurnal temperature variations in lakes have been 

 made (for example ;, Geiger, 1950); fewer studies of diiirnal changes in the 

 oceans have been made (for example, SvercLrup et al., 19^2 and Defant, 

 1961). Perhaps the most extensive account is given by La Fond (195^) who 

 considered inshore as well as deep-sea locations. Most of the oceanic 

 studies were made at anchor stations of short dxiration. Because they are 

 limited to shallow water, a comparatively large number of studies have 

 been excluded from this discussion. 



This report analyzes the results of an intensive survey conducted by 

 personnel of the I^ydrographic Office in September 1959 at Ocean Weather 

 Station ECHO (35N, kQw)o Half -hourly deep bathythermograph ^BT) casts 

 and several short series of shallow casts at 10~mlnute intervals were made. 

 In addition, 93 Nansen casts were made in connection with a study of the 

 seasonal halocline, BT data were carefully controU.ed for accuracy lay 

 reading slides immediately upon completion of an observation; instruments 

 were replaced when gross errors appeared in the data. Thirteen instru- 

 ments were used to obtain nearly 900 BT's between 2 and 21 September 1959* 

 The mean diurnal temperature changes for a mid-latitude mid-oceanic loca- 

 tion in late summer can be obtained from these observations. 



METHOD OF ANALTSIS 



All BT records were averaged for each hour of the day. Thus, the 

 average for each hour represents between 27 and ^9 observations taken dxur- 

 ing the period of the survey. The purpose of averaging is twofold; namely, 

 (1) to provide hourly values of meteorological and astronomical variables 

 for the computer prediction program, and (2) to remove or minimize hori- 

 zontal factors, mainly advection and the horizontal component of diffusion, 

 which are not used in the computer program. In addition, some of the ver- 

 tical processes average out in desirable fashion; that is, the average 

 thermal structure represents averages of cloudiness, wind (evaporation), 

 sea condition (and therefore average turbulent mixing), and local cooling 

 due to shower activity. Since the observations were taken over a period 

 of 20 days, during which times of flood and ebb tides moved forward about 

 17 hours, tidal effect has almost been removed from the data, 



* Redesignated U. S. Naval Oceanographic Office 10 July I962 



