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Tides

Explore the fascinating phenomenon of tides caused by the gravitational pull of the moon and sun. Learn about tidal amplitudes, amphidromic points, and the effect of air pressure and wind on tides. Discover how to calculate tide heights and explore interesting features like tidal bores.

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Tides

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  1. Tides Graeme Bloomfield

  2. Lunar and solar tides (2/3 v 1/3)http://www.iupui.edu/~g115/assets/mod12/spring_neap_orientation.JPG

  3. To scale….On our Earth scale: sun would be about 10m across, and over 1 Km away and the moon about 10m awayCrazy that they can make the sea level change so much

  4. Basic Modelhttp://dusk.geo.orst.edu/oceans/PPT/TidalCycleV2.htmlThe moon always looks the same (to someone out there)

  5. The moon does not orbit the earth…. They both orbit the centre of mass (just inside the Earth)

  6. Tides occur because the Earth rotates into the bulge… the bulge stays put we move in and out…. But it isn’t that simple

  7. Lots of features to deflect the bulge…..& then there is Coriolis….

  8. Coriolois(40 000 Km in 24 hr (1600Km/hr)… or ?)

  9. Our part of the world

  10. Tidal Amplitudes & amphidromic pointsThink of water sloshing about in a bath and a standing wave

  11. Perth v Nelson • Perth tides https://tides.willyweather.com.au/wa/perth/perth.html • Nelson tides http://m.metservice.com/marine/tides/nelson

  12. NZ tide movementhttps://www.niwa.co.nz/our-science/coasts/research-projects/all/physical-hazards-affecting-coastal-margins-and-the-continental-shelf/news/m2mov

  13. King tides • http://www.stuff.co.nz/nelson-mail/news/9683526/Highs-and-lows-of-king-tides • Nothing orbits in a circle…. they are elliptical, the day of that pic was a 4.7 tide in Nelson

  14. Effect of air pressure • https://www.linz.govt.nz/sea/tides/introduction-tides/meteorological-effects-tides • Barometric pressure: Tide predictions are computed for a standard barometric pressure of 1013 hectopascals (hPa) or millibars. • A difference from the average of 1 hPa can cause a difference in height of 1 centimetre. A low barometer will allow the sea level to rise and a high barometer will tend to depress it. • https://www.windy.com

  15. Effect of air pressure…. and windA storm surge is not just a big wave

  16. Other things of interesthttps://icm.landcareresearch.co.nz/knowledgebase/publications/public/tuckey_etal_tasman_bay_circulation.pdf The tidal residual, or tidally-averaged circulation is mostly associated with differences in the spatial pattern of the rising tide and the falling tide. A mean clockwise circulation in Golden Bay and a mean eastward drift across the northern boundary of the bays

  17. Mot river plumeover 1 000 000 t pa

  18. Rule of 12ths

  19. Chart datums

  20. Stephens Passageall sorts of depths

  21. How much water over that rock at 12.00 today (Nov)?Time difference c.f. Nelson is: -30 minAnd the Tide heights are 2.7 and 0.7

  22. Answer • HT will be at 9.00 (Nelson -30 min) • So at 12.00 it is 3 hrs since HT • So we have: 1/12 + 2/12 + 3/12 = 6/12 = 0.5 or exactly half way out • Nelson tidal range is 4.0 – 0.7 = 3.3 (for Nov 6) • But for Stephens it is 2.7 – 0.7 = 2.0 m (Nautical Almanac) • Half of 2.0 = 1.0 m…. This is the amount the tide has gone out • So the tide level is 2.7 – 1.0 = 1.7 m above CD • So that rock has 1.7 m of water over it

  23. Tidal Bore

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