Several statistical characteristics of astronomical tides, such as the diurnal, monthly, 

 annual, and predictable long-term variations in tidal heights are presented in Section VII. 

 Some applications of these statistical data are discussed in Section VIII. 



Section IX provides a few recommendations for improving the statistical data in any 

 revision of this work. 



Many technical terms used in the study of tides and tidal datums are defined in 

 Appendix A. Statistical data described in Sections VII and VIII for all NOS reference 

 stations and a few other locations are presented in Appendix B. AuxUiary tables needed for 

 the full use of the tables included in Appendix B are given in Appendix C. 



II. DESCRIPTION OF THE RECORDS 

 1. Astronomical Tides. 



Several important features of tlie "astronomical tide are shown by the record in Figure I. 

 This record appears as a series of nearly sinusoidal oscillations with an average period near 

 12 hours and 25 minutes. Note that the amplitude of tliese oscillations varies from one to 

 tlie next and that tlie average range of any two successive tide waves rises and falls with a 

 cycle of about 2 weeks. If a much longer period of record were shown, a cycle with a period 

 near 29 days would also be discernible. The largest amplitudes coincide approximately with 

 the time of a new Moon and a full Moon. The lowest amplitudes occur when the Moon is in 

 first or third quarter. There is an approximate reproduction of the curve after periods of 

 14.5 and 29 days; i.e., periods of Vi and 1 full lunar month. Letters and symbols (in Fig. 1) 

 indicating significant events (discussed in Sec. Ill) in the lunar orbit have been placed on the 

 graph (record). Lines connecting alternate highs and alternate lows have been drawn in the 

 figure to show that the semidiurnal wave of greatest ampUtude near N has become the 

 wave of least amplitude near S. Botli waves have nearly the same amplitude near E. 



The tidal curve in Figure 1 shows a classical semidiurnal tide. This tide behavior is the 

 most common type along the U.S. Atlantic coast, and much American tide lore seems to 

 have been derived with this type of tide phenomena in mind. Tidal curves, however, may 

 have many other shapes. Astronomical tides for January 1963 at five locations are shown in 

 Figure 2. These curves have been normalized with respect to maximum range for each sta- 

 tion to show the shape of the various curves rather than the relative range of the tide at each 

 location. Curve A for New York, New York, is another example of a semidiurnal tide. The 

 two highs and two lows of each tidal day, approximately 24 hours and 50 minutes, are more 

 nearly equal than in curves B, C, and D. Curve E for Pensacola, Florida, is a typical example 

 of a diurnal tide. Only one high and one low are clearly discernible for each lunar day. The 

 other curves illustrate intermediate types of tide. 



15 



