I. INTRODUCTION 



The Texas Tower No. 4 research operations during 1959-1960 were 

 intended to provide data from a convenient and particular ocean region 

 in sufficient detail to support analytically sound interpretation of long- 

 and short-term environmental transitions. To expedite initial information 

 acquisition in a largely unknown region, every attempt was made to use 

 readily available techniques and instrumentation. The experience and 

 information gained is now the basis for establishing more adequate 

 field systems for fixed-station observation. This report is concerned 

 with only one of the more readily observed phenomena: short-term, 

 usually anomalous variations of the water temperature structure 

 hereafter referred to as "signature" associated with a special variety 

 of internal waves. 



The existence of internal waves beneath the sea surface has long 

 been known but only recently has observation technology advanced to 

 the point of making controlled detection practical. Ekman (1904) 

 theoretically explained "dead water" in terms of internal waves 

 generated by a vessel moving slowly through a shallow overlying layer 

 of low density water. Free wave speeds that he derived (which happen 

 to closely correspond to results cited in this report) were shown to be 

 inadequate to account for propagation of internal waves of tidal character 

 until Haurwitz (1950) and Defant (1950) introduced the effect of earth 

 rotation. Meanwhile, Fjeldstad (1933) developed a theoretical analysis 

 of internal waves within a continuously varying density structure as 

 opposed to the simplified two-layer system. These works and others 

 too numerous to cite (see Davis and Patterson, 1956) were chiefly 

 concerned with oscillatory waves of relatively long period. The works 

 of Keulegan (1953) and Long (1956), which specifically consider the 

 shallow-water internal solitary wave, will be given more detailed 

 attention later in this report. 



Several attempts have been made to use ships for observing internal 

 waves in deep water over sufficient time periods to allow significant 

 statistical analysis. Reid (1956) set up repetitive measuring stations 

 off the southern California coast; a multiple ship survey was conducted 

 in the Atlantic (Brown, Corton, and Simpson, 1955); and more recently, 

 detailed time series were obtained in a special deepwater anchoring 

 system (Magnitzky and French, I960). The difficulty of performing 

 these operations has intensified interest in use of shallower water 

 fixed stations using bottom-mounted sensors (Haurwitz, Stommel, and 

 Munk, 1959) and fixed platforms (LaFond, 1959) as well as photographic 



