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Volume 14, issue 5 | Copyright

Special issue: Developments in the science and history of tides (OS/ACP/HGSS/NPG/SE...

Ocean Sci., 14, 1057-1068, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Sep 2018

Research article | 14 Sep 2018

Radiational tides: their double-counting in storm surge forecasts and contribution to the Highest Astronomical Tide

Joanne Williams1, Maialen Irazoqui Apecechea2, Andrew Saulter3, and Kevin J. Horsburgh1 Joanne Williams et al.
  • 1National Oceanography Centre, Joseph Proudman Building, 6 Brownlow St, Liverpool, UK
  • 2Deltares, Boussinesqweg 1, Delft, the Netherlands
  • 3Met Office, Fitzroy Road, Exeter, UK

Abstract. Tide predictions based on tide-gauge observations are not just the astronomical tides; they also contain radiational tides – periodic sea-level changes due to atmospheric conditions and solar forcing. This poses a problem of double-counting for operational forecasts of total water level during storm surges. In some surge forecasting, a regional model is run in two modes: tide only, with astronomic forcing alone; and tide and surge, forced additionally by surface winds and pressure. The surge residual is defined to be the difference between these configurations and is added to the local harmonic predictions from gauges. Here we use the Global Tide and Surge Model (GTSM) based on Delft-FM to investigate this in the UK and elsewhere, quantifying the weather-related tides that may be double-counted in operational forecasts. We show that the global S2 atmospheric tide is captured by the tide-and-surge model and observe changes in other major constituents, including M2. The Lowest and Highest Astronomical Tide levels, used in navigation datums and design heights, are derived from tide predictions based on observations. We use our findings on radiational tides to quantify the extent to which these levels may contain weather-related components.

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Short summary
Tide predictions based on tide-gauge observations are not just astronomical tides; they also contain periodic sea level changes due to the weather. Forecasts of total water level during storm surges add the immediate effects of the weather to the astronomical tide prediction and thus risk double-counting these effects. We use a global model to see how much double-counting may affect these forecasts and also how much of the Highest Astronomical Tide may be due to recurrent weather patterns.
Tide predictions based on tide-gauge observations are not just astronomical tides; they also...