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tide station location. A change in relative mean sea level
R may be composed of both an absolute mean sea level
R2 Smaller solar elliptic constituent. This constitu- change component and a vertical land movement change
ent, with T2, modulates the amplitude and frequency of S2 component.
for the effect of variation in the Earth's orbital speed due residual current The observed current minus the
to its elliptical orbit. astronomical tidal current.
Speed = 2T + h p1 = 30.041,066,7° per solar hour. response analysis For any linear system, an input
race A very rapid current through a comparatively function Xi(t) and an output function X0(t) can be related
narrow channel. according to the formula:
radiational tide Periodic variations in sea level X0(t) = o Xi (t )W( )d + noise(t)
primarily related to meteorological changes such as the where W( ) is the impulse response of the system and its
semidaily (solar) cycle in barometric pressure, daily Fourier transform:
(solar) land and sea breezes, and seasonal (annual) changes Z(f) = o W ( )e-2 if = R(f)ei (f)
in temperature. Other changes in sea level due to is the system's admittance (coherent output/input) at
meteorological changes that are random in phase are not frequency f. In practice, the integrals are replaced by
considered radiational tides. summations; Xi, W, and Z are generally complex. The
range of tide The difference in height between discrete set of W values are termed response weights;
consecutive high and low waters. The mean range is the X0(t) is ordinarily an observed tidal time series and Xi(t)
difference in height between mean high water and mean the tide potential or the tide at some nearby place. A future
low water. The great diurnal range or diurnal range is the prediction can be prepared by applying the weights to an
difference in height between mean higher high water and appropriate Xi(t) series. In general:
mean lower low water. For other ranges see spring, neap, Z = R(f) and Tan(Z) = (f)
perigean, apogean, and tropic tides; and tropic ranges. measure the relative magnification and phase lead of the
real-time Pertains to a data collecting system that station at frequency f.
monitors an on-going process and disseminates measured reversing current A tidal current which flows al-
values before they are expected to have changed ternately in approximately opposite directions with a slack
significantly. water at each reversal of direction. Currents of this type
rectilinear current Same as reversing current. usually occur in rivers and straits where the direction of
red tide (water) The term applied to toxic algal flow is more or less restricted to certain channels. When
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the movement is towards the shore or up a stream, the S
current is said to be flooding, and when in the opposite s Rate of change (as of January 1, 1900) in mean
direction, it is said to be ebbing. The combined flood and longitude of Moon.
ebb movement (including the slack water) covers, on an s = 0.549,016,53° per solar hour.
average, 12.42 hours for a semidiurnal current. If S1 Solar diurnal constituent.
unaffected by a nontidal flow, the flood and ebb Speed = T = 15.000,000,0° per solar hour.
movements will each last about 6 hours, but when S2 Principal solar semidiurnal constituent. This
combined with such a flow, the durations of flood and ebb constituent represents the rotation of the Earth with
may be quite different. During the flow in each direction respect to the Sun.
the speed of the current will vary from zero at the time of Speed = 2T = 30.000,000,0° per solar hour.
slack water to a maximum about midway between the S4, S6 Shallow water overtides of the principal solar
slacks. constituent.
reversing falls A name applied to falls which flow Speed of S4 = 2S2 = 4T = 60.000,000,0° per solar hour.
alternately in opposite directions in a narrow channel in the Speed of S6 = 3S2 = 6T = 90.000,000,0° per solar hour.
St. John River above the city of St. John, New Brunswick, Sa Solar annual constituent. This constituent, with
Canada, the phenomenon being due to the large range of Ssa, accounts for the nonuniform changes in the Sun's
tide and a constriction in the river. The direction of flow is declination and distance. In actuality, they mostly reflect
upstream or downstream according to whether it is high or yearly meteorological variations influencing sea level.
low water on the outside, the falls disappearing at the Speed = h = 0.041,068,64° per solar hour.
half-tide level. Ssa Solar semiannual constituent. See Sa.
rho ( ) Larger lunar evectional diurnal constituent. Speed = 2h = 0.082,137,3° per solar hour.
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Speed = T 3s + 3h p = 13.471,514,5° per solar hour. salinity (S) The total amount of solid material in
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