1 - NGA

tfdal bench mark-A bench mark S* to
reference e tide staff HI a tidal .5tafien and tha
elevation of which is determined with relation to
the local tidal datum.
tidal constltuont—See constituent.
tktal corractlo~A mrrecfion aoolied to
grsvifdioml observations to retie the effect
of Earth t“~s on grsvimetric absarvat”ms.
tidal current chait-A chart showing, by
arrows and numbers, the average direden and
speed of Mel currents at e pwlicular pen of the
currem cycle. A numbsr of such charts, one fer
each hour of the current WCle, usualfy are
published together.
tldel current-The efterneting horizontal
movement of water eaaecialad wilh the rise and
tell of the tide causad by the astronomic tidepmducing
forcas.
tidal datum plana-See tldel datum.
tidal datu~Specific tide levels which era
used as aurtaces ef reference for depth
measuremems in the sea end es a base for the
determination of elevalion on fend. Many
different datums have baen used, perkularly for
leveling operetiens. Also called tidal detum
plane.
tidal day—See lunar day.
tidal varlatlon of gravity-Periodic
deviations fmm normal of the gravity on Earih
and the dkactbn of the plumb fine caused by
the eftractkm of the Mean and the Sun’s mess,
tlda gage-A devke for measuring the height
of tide, It may be simpfy a graduated staff in a
sheffered fecelion wtrare visual ebservetiena can
be made at any desired time; or if may consist
of an elaborate reading instrument mskfng e
centinueus graphic record of tide haight egeinst
time, Such an “instrument is usualfy actuated by
a fled in a pipa communicating wth the see
threugh a small hefe WMch filters out shorter
waves. See elso float gage; nonrecordirtg
gage; portable ●utometlc tide gage:
prossuro gage; self-registering gage;
staff gaga; atettdard automatic tide
gag..
tldo loval—See mean tide Iavel.
MIL-HDBK-850
258
tide ovyr run-A reprintof a c5erl or rruip
nacaasfatd by unusual condiiiens before
extensive revisions can be accompiiied. Also
celled ●morgency run.
tlda station-A pface al whti tide
cbaervetiens ara made. See also prlmaty tide
station; secondary tido ●tatlon.
tlda-producing force(s)-lhe slight kcef
dflerence between the gravitational aftrhcfion of
fww astronem’k bcdies and the centrifugal force
that hofda fhem aIMrf. These forces are wrecffy
equal end eppcdfe at the cerrfer of gravity of
eifhar of the tcdiis, but, since gravtiationel
attredkm is invereetj proportional to the square
of the distance, if varies frcm point 10 peint on
the surtam et the bedies. Therafore,
gravifationsl aftracficrn predominates at the
surface paint nearest to the other body, while
centrifugal repulsion predominates et the
surface point farrhest from the other bedy.
HerWe, Ihere are Iwo regmns wlrere IiOepmducing
forcaa are at a maximum, and
normslfy there are two tides each lunar day end
seler day.
., .,. .= ... 4,.
tldnmark—1. A high wcter mark left by tidal
water. 2. The highest point reached by a h}gh
tide. 3. A mark placed 10 indicate the htghest
point retched by a high tide, or eccseicdfy,
any specified state of tida.
tide-The periodic rise and fall et the surface of
the ecean resufting fmm the grevifational
anraction of tha Moon and Sun acting upon the
rotating Earth. See alse age of diurnal
Inequality; age of parallax Inequality;
age of phase lnaquallty; ●mphldromic
point; amphldramic roglon; ●nnual
Inequality; anomallatic tide cycla;
apogaan tldaa: constituent; constltuant
day; corrected establlehment: cotldal
hour; degenerate ●mphldromlc ●yetem;
diurnal constftuant; diurnaf Inequality;
abb tlda: ●stablishment of tha port;
flood tlda; harmonic constants; height
of the tida; high watar; high water Iino;
higher high wete~ higher high watar
Interval; higher low water; higher low
water Intarval; Indian spring low wate~,
Indian tldo plana; International low
wate~ low water; low water full and
change; low water Ilna; Iowar high
water; lower high water Intarval; Iowar
low wetafi Iowar low watar intarval;
lowest low watar; Iowaet low water