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2011 The explanation of tides in 11 steps Marc Philippart Rijkswaterstaat

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2011 Generation of tides main drivers are Moon and Sun explaining the tides in 11 steps

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Rijkswaterstaat 2011 Step 1: gravity force of moon No continents, just water (equilibrium tide) Only influenced by attraction of the moon moonearth

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Rijkswaterstaat 2011 Step 2: centrifugal force If this was the only force, the moon would crash on the earth Also centrifugal force due to rotation around centre of gravity

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Rijkswaterstaat 2011 Step 3: combined forces gravity centrifugal combination

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Rijkswaterstaat 2011 Step 4: twice a day? twice a day would mean every 12 hour however, we see 12 hour and 25 minutes where is this ‘error’ of 50 minutes a day ? moon travels around earth in days after one full earth rotation moon travels also 13 dgr t=24h50 23h56 t=o 13º 54 min.

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Rijkswaterstaat 2011 Step 5: the sun sun acts the same as moon amplitude ca 25% of moon rotation of earth: 23 h 56 minutes t=o (by definition)t=24h00 1º = 4 min. 23h56 eg. at 12h, sun in South after 23h min, sun in South

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Rijkswaterstaat 2011 Step 6: the sun moon interaction effect of tide by moon

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Rijkswaterstaat 2011 Step 6: the sun moon interaction sun and moon work together: Spring Tide during full moon and during new moon

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Rijkswaterstaat 2011 Step 6: the sun moon interaction sun and moon work opposite: Neap Tide firts quarter and last quarter of the moon

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Rijkswaterstaat 2011 Step 7: diurnal inequality inequality due to the declination of earth axis 23,5º declination equator rotation of earth h2 h1 equator rotation of earth

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Rijkswaterstaat 2011 Step 7: diurnal inequality spring tide neap tide cycle sensitive

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Rijkswaterstaat 2011 Step 8: variation in driving forces distance moon to earth varies (ellipsoid, 27,55 day) direction ellipsoid varies in 8,85 yr. distance sun to earth varies plane of moon varies 5 degrees around 23,5 (18,61 yr.) plane of sun varies with the precession ( yr.)

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Rijkswaterstaat 2011 Step 9: continents & coriolis the equilibrium tide runs around the southern hemisphere further it travels around the world with a delay tides in the north sea are more than 2 days old the coriolis force (due to rotation of the earth) influences the tides

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Rijkswaterstaat 2011 Step 9: continents & coriolis

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Rijkswaterstaat 2011 Step 10: non-lineair effects due to bottom friction the tide will deform allthough the driving forces consist of 2 forces, called M2 (moon) and S2 (sun), at our coast a set of nearly 200 components are needed to reconstruct the tide

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Rijkswaterstaat 2011 Step 11: wind effects due to meteorological influences the actual tide differs surge bij NW storm negative surge by Easterly winds

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Rijkswaterstaat 2011

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Rijkswaterstaat 2011 Forecast of tides there are two ways of forecasting (predicting) 1: harmonical analyse and composing observed tide > decomposing > reconstruction 2: modelling calibrating model > meteo input > result

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Rijkswaterstaat 2011 harmonic analyse of tide observed predicted decompositioncontinuation of decomposition

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