Fróðskaparrit - 01.01.1975, Side 78

86
Sea Level Fluctuations in Tórshavn, Preliminary Results
ments r,s,h,p,N,p’ involved in the motions of the Earth and
Moon in their orbits. As the elements vary almost linearly in
time the (almost) constant frequencies foi emerge, giving rise
to the harmonic constituents of the tide. The harmonic con-
stants Hj and g; (amplitude and Greenwich phase lag) must
be determined empirically and separately for each place, while
the f . may be calculated theoretically to a very high precision.
The most significant constituents have been given symbols
and the identification of the harmonics found in the tide of
Tórshavn is in almost all cases quite straight-forward by com-
paring observed frequencies to theoretical ones. Symbols and
theoretical frequencies are listed in the last two columns of
table III for those constituents identified. The phase constants
of table III are relative to the time origin of the data series.
Eor this origin one may, using the formulas cited in ref. 12,
determine the values of the astronomic elements measured at
Greenwich and from these evaluate the Greenwich Phase lags
g; of formula (9). Furthermore the amplitudes and phase lags
of constituents may be corrected for nodal modulation, that is
for the interference of smaller, unanalysable, constituents lying
close in frequency (ref. 11 and 12).
Table IV lists amplitudes and Greenwich Phase lags for the
identified constituents corrected for nodal modulation along
with global characteristica. The last column of table IV lists
the local time lags. The Equilibrium theory would require
these lags to be zero.
A thorough discussion on the lags and on the relative strength
of the various constituents will be given in a separate paper,
but some salient features may be touched upon here.
When corrected for nodal modulation M2 is not the largest
constituent, but rather 0( which is remarkable especially in
view of the marked semidiurnal dominance in the currents.
In a series of current measurements performed by the author
in the summer of 1974 at a position only about 1 km distant
from the tide gauge, a preliminary analysis of the current gave
an amplitude for M2 nearly 12 times larger than that of 0t.