IMS 14 - Tides

Tides

Properties

-          Periodic raising & lowering of avr sea lvl

-          Edge slowly shift landward / seaward daily

-          Long regular shallow-water wave

-          Wavelength 1000 km, height > 15 m

-          By Sun Moon attraction

Gravitational Forces

·         Every mass particle in universe attracts another

·         Proportional to product of their mass

·         Inversely proportional to the square of distance between the masses

Side facing Moon - bulge due to gravity > centripetal

Side away Moon – bulge due to centripetal > gravity

Max tide-generating force @ latitude 28.5° from equator

 High tides @ most places every 12 hrs 25 min (depend lunar day, not solar day)

Lunar Day

·         Moon on meridian every 24 hrs 50 min

Solar Day

·         Sun on meridian every 24 hrs

Solar bulges = 46% Lunar bulges coz massive but far

Lunar cycle = monthly tidal cycle

        = 29.5 days

                    = time Moon takes to complete orbit :� t " ,� @͏ Roman"'>          Wavelength 1000 km, height > 15 m

-          By Sun Moon attraction

Gravitational Forces

·         Every mass particle in universe attracts another

·         Proportional to product of their mass

·         Inversely proportional to the square of distance between the masses

Spring tide @ full new moon; lunar & solar bulges constructively interfere – large tidal range

Neap tide @ quarter moon; lunar & solar bulges destructively interfere – small tidal range

Elliptical orbits

·         148.5 million km Earth-Sun distance @ N hemisphere winter

·         152.2 million km Earth-Sun distance @ N hemisphere summer

·         Most areas 2 high 2 low tides

Tidal Pattern

·         Landmass, various depths, sizes, shapes of basins

·         Diurnal tidal pattern

ü  Common in shallow inland sea; One high one low tide / lunar day; 24 hrs 50 min

ü  Mexico Gulf, SE Asia

·         Semidiurnal tidal pattern

ü  2 high  2 low tides / lunar day; Approximately same

ü  East Australia coast, New Zealand, Atlantic USA coast

ü  12 hrs 25 min

·         Mixed tidal pattern

ü  2 high / low diff heights

ü  12 hrs 25 min

ü  Pacific coast of N America

Tidal bore / benak

·         Solitary wave formed when rising tidal front enter Shallow Narrow River of high tidal range from a wide estuary

·         In Malaysia, tidal bore phenomenon can be seen at Batang Lupar, Batang Sadong, Batang Samarahan and Batang Saribas, Sarawak.

·         Velocity of tidal bore is 7 km/hr - 18km/hr heights > 3 m