EM 1110-2-1100 (Part II)
30 Apr 02
NOS Tidal Constituents and Arguments
(j) The value κ is approximately constant at every location in the world because it represents the actual
lag between the passing of the tide-producing force (i.e., moon) at a specific location and the following high-
tide contribution of that force at that same location. It is computed as the sum of the theoretical phase or time
lead of the tide-producing force relative to the observer at some fixed time and the measured phase lag ζ from
the observer at that fixed time to the following high water. The theoretical location of the tide-producing force
is referred to as the equilibrium argument (V0 + u). In Figure II-5-10, the tide-producing force and
corresponding equilibrium tide at location M are located (V0 + u) degrees ahead of point T. Conversely, the
equilibrium tide will be located at point T if shifted (V0 + u) degrees. The value of ζ represents the phase lag
from point T to HW.
(k) The equilibrium argument (V0 + u) is computed from equations defining the time-varying relationship
between the earth, moon, and sun. The value of ζ is computed from observed tidal time series data. As
stated, the sum of these two values is approximately constant for any fixed location at any time.
(l) Values of the equilibrium argument for the constituents of Table II-5-3 relative to the passing of the
tidal potential force at the Greenwich meridian for each calendar year from 1850 through 2000 are tabulated
in Schureman (1924). An example is shown in Table II-5-5 for the years 1990 to 2000. Monthly and daily
adjustment tables are also presented. Each of the values is computed according to the respective constituent
speeds shown in Table II-5-3. The equilibrium arguments tabulated in Schureman are referenced to the
meridian of Greenwich; therefore, the argument (V0 + u) represents the phase difference in degrees between
the location of the tidal potential term (moon or sun) and Greenwich relative to some specific time.
Water Levels and Long Waves