(m) A tidal simulation computer program is available in ACES (Leenknecht, Szuwalski, and Sherlock

1992) to compute nodal factors and local (or Greenwich) equilibrium argument values for any time period

and generate the corresponding water surface time series as a function of input constituent amplitudes.

Formulas for computing the equilibrium arguments are found in Shureman (1924), but are too lengthy for this

manual.

(3) Harmonic reconstruction.

(a) In order to reconstruct a tidal series for a specific time and location, the various phase arguments

of Equation II-5-16 must be defined according to local conditions. Generally, local values of *κ*n, H0, and *H*n

are available from NOS harmonic analyses. Because the values of the nodal factors *f*n are slowly varying,

the yearly values determined according to Schureman are sufficiently accurate for the particular time of

interest throughout the world. However, local values of (*V*0 + *u*)n vary with the speed of the constituent and

have to be determined for the location and time of interest. This information can be computed from tabulated

equilibrium arguments relative to Greenwich such as those presented in Schureman or computed with

programs developed for that purpose such as those contained in ACES.

(b) Values of the local equilibrium arguments, i.e., local (*V*0 + *u*)n, represent the instantaneous value of

each of the equilibrium tide-producing force constituents (in degrees) with respect to some specific point on

the earth; for example, the time-varying location of the moon and sun with respect to some location on the

earth. Referring to Figure II-5-11, the horizontal axis represents distance with the point *G *representing

Greenwich, England, and *O *representing an observer located at some point west of Greenwich. The location

of the moon with respect to Greenwich at longitude 0o at Greenwich time *t*0 is indicated by the Greenwich

equilibrium argument presented in Shureman, denoted as Greenwich (*V*0 + *u*), for time Greenwich *t*0.

II-5-18

Water Levels and Long Waves

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