We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
A Combined Modeling and Measurement Approach to Assess the Nodal Tide Modulation in the North Sea.
- Authors
Hagen, Robert; Plüß, Andreas; Jänicke, Leon; Freund, Janina; Jensen, Jürgen; Kösters, Frank
- Abstract
The correct representation of the 18.61‐year nodal tide is essential for an interpretation of the evolution of mean sea level, as errors cause misleading bias. The nodal tide is currently estimated by applying correction factors in harmonic analysis, which are derived from the equilibrium tide. From the equilibrium tide, correction values f for amplitude and u for phase are determined, which alter lunar tidal constituents, depending on the nodal cycle. This approach has proven to be valid for many tide gauges, even though the impact of the nodal tide in shelf seas has been shown to differ from their theoretical correction value. Hence, tidal constituents from tide records in the North Atlantic shelf region were analyzed for their nodal amplitude and phase lag with a new multiple, nonlinear regression approach, which is able to approximate the nodal modulation quantitatively and its agreement to the theoretical equilibrium tide. Results show an overestimation of the lunar M2 and N2 constituents by the equilibrium of more than 2.7% in the Wadden Sea, while O1 and K2 are underestimated by 1–4.6%, which would produce an error of 2–5 cm for example, in the German Wadden Sea. Additionally, a process‐based model of the North Sea was applied at the diurnal minimum and maximum of the nodal cycle to calculate a spatial distribution of f and u. Results confirm the spatially varying nodal satellite modulation in friction dominated, shallow water regions. Plain Language Summary: The nodal tide is a part of the tidal regime, which changes the tidal range on a reoccurring timescale of 18.61 years, originating from the gravitational force of the moon. A nodal amplitude can be up to 30 cm, which makes its accurate consideration essential for the analysis of sea‐level rise. In recent studies, the influence of the nodal tide is approximated percentage‐wise, as its reoccurrence interval is too long for conventional analysis. This study has found, based on 31 tide records in the European North Sea, that current analysis methods are inaccurate in the Northern English Channel and the Wadden Sea by several centimeters based on the influence of the nodal tide. This is analyzed with a new procedure, which uses statistical methods to approximate the nodal tide from measured tide records. We conclude, that an imprecise estimate is restricted to shallow and geometrically complex parts of the North Sea. As most tide gauges are located near the coast in shallow water, these findings may have major implications on the correct approximation of the mean sea level (MSL). Key Points: Nodal modulation can be extracted from tide records through multiple, nonlinear regression fitting of annually analyzed tidal constituentsTheoretical nodal modulation, derived from the equilibrium tide theory, does not apply consistently in the North SeaFriction causes the generation of shallow water tides, which influence the nodal modulation of lunar constituents and S2 significantly
- Subjects
NORTH Sea; NORTH Atlantic Ocean; TIDES; CONTINENTAL shelf; SEA level; HYDRODYNAMICS
- Publication
Journal of Geophysical Research. Oceans, 2021, Vol 126, Issue 3, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2020JC016364