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

Abstract

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.

A nonstationary analysis for investigating the multiscale variability of extreme surges: case of the English Channel coasts

“…The finding is in agreement with the previous works of Lee et al (2017) and Wong (2018) highlighting the importance of a careful consideration when complex physical mechanisms of different climate indices are included in model structures for estimating extreme surges. Indeed, this work provides guidance on incorporating nonstationary processes of large-scale oscillations into different spectral components informed by the wavelet techniques, the Bayesian approaches and the GEV model probabilities.…”

“…Available data are summarized as the following: Brest (168 years between 1850 and 2018), Cherbourg andDunkirk (54 years between 1964 and2018), Dover (53 years between 1963 and 2018), Weymouth (28 years between 1990 and 2018).…”

“…A year-by-year tidal simulation (Shaw and Tsimplis, 2010) has been applied to the sea level time series to determine the amplitude and the phase of tidal modulations using harmonic analysis fitted to 18.61-, 9.305-, 8.85-and 4.425-year sinusoidal signals (Pugh, 1987). The radiational components have also been considered for the extraction of the stochastic component of surges (Williams et al, 2018).…”

“…As suggested by Wong (2018), including a wider range of physical process information and considering nonstation-ary behaviour can better enable modelling efforts to inform coastal risk management. In his work, he has developed a new approach to integrate stationary and nonstationary statistical models and demonstrated that the choice of covariate time series should affect the projected flood hazards.…”

Seasonal variability of radiation tide in Gulf of Riga

“…1. Therefore, there should be notable S 1 tidal component with oscillation period of exactly 24 h (Williams et al, 2018). Nature of S 1 tide is more related with diurnal changes in atmosphere caused by radiation rather than gravitational effect of the Moon and the Sun (Ray and Egbert, 2004).…”