A. Boesch and S. Müller-Navarra: Reassessment of long-period constituents for tidal predictions 
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www.ocean-sci.net/15/1363/2019/ 
Ocean Sci., 15,1363-1379, 2019 
Residuals of high and low water times 
0 50 100 150 200 250 300 350 
Days since 01.01.2016 
Figure 14. The residuals of high- and low-water times for the tide 
gauges Cuxhaven (a) and Hamburg (b). 
dictions with the HRoI for German tide gauges starting with 
the BSH tide tables for the year 2020. 
In future work, extensive comparison of the HRoI with the 
common harmonic method might provide more insights into 
the capabilities of both tidal analysis techniques. The Ger 
man Bight would be an ideal area of investigation with its 
large network of tide gauges located both at the open North 
Sea and far within tidally influenced rivers. 
Data availability. The tide gauge observations used in this research 
are available from the respective authorities (cf. Table Al ). 
7 Conclusions 
Time series of high- and low-water records from 111 Ger 
man tide gauges were analysed to determine important 
long-period partial tides. Generalized Lomb-Scargle pe- 
riodograms were calculated from lunitidal intervals and 
heights for all tide gauges, and spectral peaks were identified 
in these periodograms above noise thresholds. The separate 
analyses of lunitidal intervals and heights were combined to 
realize one comprehensive list of partial tides. An applica 
tion is the usage of these constituents in tidal analyses and 
predictions with the HRoI. 
The new set of 39 partial tides largely confirms the pre 
viously used set with 43 partial tides. It can be seen from 
Table 2 that nine new constituents were added and 13 con 
stituents were removed. Many of the removed angular veloc 
ities are close to strong partial tides, such as the anomalis 
tic month (Mm), the half synodic month (MSf) and the half 
tropical month (Mf). The removed constituents might have 
been artefacts from spectral leakage, which are most promi 
nent in the proximity of strong spectral lines and which were 
misidentified as true signals in previous studies. The unam 
biguous identification of partial tides is very difficult at angu 
lar velocities below approximately 1° tn -1 because the noise 
levels in the periodograms increase towards lower angular 
velocities and the results from different tide gauges are less 
consistent. 
The verification based on observations from 98 tide gauges 
in the year 2016 suggests that the usage of the new con 
stituents list can lead to slightly better predictions. In par 
ticular, the average standard deviations of the residuals are 
lower and four frequencies were reduced. 
This study presents for the first time a thorough investiga 
tions of the long-period constituents used with the HRoI. The 
new list of constituents will be used in tidal analyses and pre