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2011 The explanation of tides in 11 steps Marc Philippart Rijkswaterstaat.

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Presentation on theme: "2011 The explanation of tides in 11 steps Marc Philippart Rijkswaterstaat."— Presentation transcript:

1 2011 The explanation of tides in 11 steps Marc Philippart Rijkswaterstaat

2 2011 Generation of tides main drivers are Moon and Sun explaining the tides in 11 steps

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

4 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

5 Rijkswaterstaat 2011 Step 3: combined forces gravity centrifugal combination

6 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.

7 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

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

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

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

11 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

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

13 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.)

14 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

15 Rijkswaterstaat 2011 Step 9: continents & coriolis

16 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

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

18 Rijkswaterstaat 2011

19 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

20 Rijkswaterstaat 2011 harmonic analyse of tide observed predicted decompositioncontinuation of decomposition


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