9 Why do the tides in the North Sea look like this ? Tidal waves enter into North Sea throughnorthern boundary and English Channel.Phase propagation is c = (g * depth)1/2, g = 9.81 m/s2(depth = 40 m c = 20 m/s = 72 km/h)Due to Earth rotation, tidal waves are Kelvin waves,leaning on a coast to the right.Energy loss due to bed friction: tidal waves loosepower during their journey through the North Sea.
10 Tidal chart for the M2 tide full lines: amplitude dashed: phase (Source: POL)
12 M2 tidal chart of Southern North Sea Amphidromic pointM2 tidal chart of Southern North SeaPrandle, 1981
13 Tidal propagation into the Baltic Sea is blocked !
14 Tides in the Wadden Sea (as seen in 200 m resolution model)
15 Wadden Sea model: M4 tidal elevations (phase and amplitude) as validation data.Gräwe et al., in prep.
16 Seasonality of tidal forcing How does this affectsediment transportdue to tidal asymmetries (M4)?Gräwe et al. (in prep.)Müller et al. (in prep.)
17 Stratification in the North Sea Besides tides, seasonal stratification is characteristic for the North Sea dynamics.Annual cycle of tempraturestratification in theNorthern North Sea(as seen from a 1D model)Bolding and Burchard (2002)
18 Stratification is spatially not homogeneous Tidal frontDoggerbankDoggerbankModel results by Burchard & Bolding, 2002
19 Tidal frontsTidal fronts (stratified in deep, mixed in shallow water) are an environmentally very important phenomenon.Thus, in shallow water the bottom sediment is in direct contact with the surface waters, whereas in deeper waters, the bottom layers are clearly separated from the surface wates.
20 What determines the position of tidal fronts ? Stabilising: water depth H, surface buoyancy flux Q(heat flux, net precipitation).Destabilising: tides given as tidal velocity amplitude u.Important parameter by dimensional analysis:(Q * H) / u3Large: stably stratified; Small: mixedNote: H / u3 is the famous Simpson-Hunter (1974) parameter.
21 Tidal mixing fronts in the Irish Sea stratified & deepmixed & shallowmixed & very shallow & warmorstratified due to river run-offSatellite images courtesy Alejandro Souza
22 Tidal Mixing fronts in the Irish Sea Stratification Simpson-Hunter parameterNumerical model result, Souza et al., in press.