Fróðskaparrit - 01.01.1975, Side 80

88
Sea Level Fluctuations in Tórshavn, Preliminary Results
Further one notes that in addition to the diurnal there is a
strong influence from higher harmonics. Grouping the consti-
tuents according to approximate period and for each group
calculating the ratio of the sum of amplitudes in the group
to the sum of amplitudes in the diurnal group the following
ratios appear:
Period ratio: 24h 12h 8h 6h 4h 2.5h
12h 12h 12h 12h 12h 12h
Amplitude ratio: 1 1 1 1 1 1
1.06 1 20.3 3.3 4.8 26.6
Roughly speaking the tide is 5 parts Diurnal, 5 parts Semi-
diurnal and 3 parts higher harmonics.
The peak labeled Ssa is the only low frequency peak of
astronomic origin unambigously present in the spectrum. It is
seen very clearly on fig. 4. One might expect such a longperiod
constituent to be strictly Equilibrium. The Equilibrium ampli-
tude is however only about 0.8 cm (ref. 13). The fact that Ssa
is nonequilibrium is a well known fact, Maximov (as cited by
Lisitzin ref. 13) gives for the North Atlantic north of 60 deg
latitude an amplitude of 3.3 cm and a phase lag of 48 degrees,
which compares favourably with table IV.
Prediction Prediction of the tide in the harbor of Tórshavn
has little practical importance, on the other hand sea level and
currents must be correlated in some way so that prediction of
one may yield information on the other and of the two sea
level is by far easier to measure and is the only one for which
timeseries of reasonable length exist. Therefore a computer
program was implemented to predict the tide in Tórshavn for
a period starting any given time. In the program the six astro-
y mynd. Samanburður millum spádda og mátaða flóð í Havn. Yvireftir
cr tíðin sett, frá 15. aug. 1974 kl. 0000 til 21. aug. 1974 kl. 23.45. Uppeftir
er sett hæddin á flóðini. Munurin stavar serstakliga frá broytingum í
lufttrýsti.