Tides

Tides

Periodic rise and fall of sea level due to earth's rotation and the gravitational effects of the moon and sun

Tidal range

Difference in height between high and low tide

Gravitational forces

Derived from Newton's Law of Universal gravitiation

attracted

Every object that has mass in the universe is ... to each other object

smaller gravitational force

Small object/larger the distance equals

larger gravitational force

Larger object/smaller the distance equals

Zenith

Greatest force at....(point closest to moon)

Nadir

Least force at ...(point furthest from the moon; opposite zenith)

- gravity

- motion between earth, moon, and sun

Tides are caused by a combination of...

Barycenter of moon and earth

Common center of mass/beneath earth's surface

- Center-seeking force

- Keeps planets in orbit via gravitational attraction

- Tethers earth + moon to each other

What is the centripetal force?

Resultant forces

Mathematical difference between gravitational + centripetal forces

together

Both gravitational and centripetal forces either works together or not. In the case of tides, they work...

vertical

Where resultant forces are ... relative to earth's surface: No tide generation

parallel

Where resultant forces are ... to earth's surface: Hydrostatic pressure

moon

Water bulges both away and towards the ... impacts the tides

Tidal bulges: sun's effect

Similar to lunar bulges but much smaller/moon closer to earth, exerts greater gravitational force

384,000km

Moon is .... away from the earth

between

Sun never passes ... the earth and moon

Phases

... of the moon impacts the tides

New moon

Moon between earth and sun, cannot be seen from earth

Waxing crescent

Moon moving from new to first quarter

Quarter moon

Moon appears half lit

Waxing gibbous

Moon moving from first quarter to full

Full moon

Moon and sun opposite

Waning gibbous

Moon moving from full to last quarter

Quarter moon pt.2

Moon appears half lit

Waning crescent

Moon moving from last quarter to new moon

Spring tides

New or full moons/tidal range greatest/syzygy

Syzygy

When earth, moon, and sun (or moon, earth, and sun) are all alined

Neap tides

Quarter moons/tidal range least/quadrature/destructive interference

Quadrature

Moon is 90 degrees from the earth

- Perigee

- Apogee

- Proxigean tides

What are some complicated factors (elliptical orbits)

perigee

Moon closest to earth/tidal range greatest

apogee

Moon furthest from earth/tidal range least

proxigean tides

Spring tide + perigee/exceptionally high tidal range/every 1.5 years or so

Declination

Angular distance of the moon or sun N or S of earth's equator

Sun max

23.5 degrees north or south of equator

moon max

28.5 degrees north or south of equator

equal tides

Overhead of equator

unequal tides

Shifted from equator

tidal period

Time between high tides

equilibrium theory

12 hrs and 25 minutes

Lunar day

Time between two successive overhead moons/24 hrs, 50 mins

solar day

Time between 2 successive overhead suns/24 hrs

Idealized tide prediction

2 high tides or 2 low tides per lunar day/6 lunar hours between high and low tides

- Continents and friction with seafloor modify tidal bulges

- Tides are shallow-water waves with speed determined by depth of water

- Idealized tidal bulges cannot form

- Cannot keep up with earth's rotation

What is part of the dynamical theory?

Amphidromic point

Crests and troughs of tides rotate around...

tidal range

There is no .... at the amphidromic point

Cotidal lines

Simultaneous high tide

12

Tide wave rotates once in ... hours

- Diurnal

- Semidiurnal

- Mixed

What are the names of the 3 tidal patterns?

Diurnal

One high or one low tide per day

Semidiurnal

Two high or two low tides per day/tidal range about same

Mixed

Two high or two low tides per day/tidal range different/most common

- Rapidly spinning seawater

- Restricted channel connecting two basins with different tidal cycles

- Maelstrom near Arctic Norway

What are the characteristics of a whirlpool?

Tidal bores

Tide-generated wall of water that moves up certain rivers

- Large spring tidal range of at least 6m (20ft)

- Abrupt flood tide and short ebb tide

- Low-lying river with seaward current

- Shallowing of landward sea floor

- Narrowing of basin in upper reaches

What are the conditions needed to create a tidal bore?