Tides

1
Tides
2
Tides are generated by

• Gravitational pull of the moon and sun
• Centripetal force of the rotating Earth

3
Tides are generated by

• the gravitational pull of the moon and sun
• - moon has 2x greater gravitational pull than
  the
• sun
• - sun is 10 million x more massive than the
• moon and is 390 times farther away

4
Centripetal force
5
GRAVITATIONAL FORCE
CENTRIPETAL
GRAVITATIONAL CENTRIPETAL
6
Tidal Cycles

• Diurnal Tide 24 hr 50 min cycle
• Semi Diurnal Tide 12 hr 25 min cycle
• Mixed Tide 12 hr 25 min cycle

7
Description of tides

• High water a water level maximum ("high tide")
• Low water a water level minimum ("low tide")
• Tidal range the difference between high and low
  tide
• Spring Tide full moon and new moon (14.77 days)
• Neap Tide 1st quarter and 3rd quarter (14.77
  days)

Intertidal zone
High tide
Low tide
8
The monthly tidal cycle(29½ days)

• About every 7 days, Earth alternates between
• Spring tide
• Alignment of Earth-Moon-Sun system (syzygy)
• Lunar and solar bulges constructively interfere
• Large tidal range
• Neap tide
• Earth-Moon-Sun system at right angles
  (quadrature)
• Lunar and solar bulges destructively interfere
• Small tidal range

9
Earth-Moon-Sun positions and the monthly tidal
cycle
Spring Tide Highest high tide and lowest low tide
Neap Tide Moderate tidal range
10
(No Transcript)
11
(No Transcript)
12
Tidal Patterns
Semidiurnal tides- two high and two low per day
Cape Cod, MA (high latitudes) Diurnal tides- one
high and one low per day Mobile, AL (low
latitudes) Mixed pattern tides- Two high and two
low tides per day BUT with successive high tide
levels that are VERY DIFFERENT from each other
Hawaii (mid latitudes)

• Type of tide depends on
• Position on the globe
• Water depth
• Contour- shape of ocean basins

13
(No Transcript)
14
(No Transcript)
15
Tidal Range
56 ft
6 ft
16
The Bay of Fundy Site of the worlds largest
tidal range

• Tidal energy is focused by shape and shallowness
  of bay
• Maximum spring tidal range in Minas Basin 17
  meters (56 feet)

17
Alma at High Tide
Alma at Low Tide
18
La Rance tidal power plant at St. Malo, France.
19
Tidal bore a true tidal wave

• Wall of water that moves upriver
• Caused by an incoming high tide
• Occurs in some low-lying rivers
• Can be large enough to surf or raft

20
Corals exposed to air at extreme low tide
21
Tidal Information
http//life.bio.sunysb.edu/marinebio/mbweb.html
HAWAIIAN ISLANDS Mean Spring Mean Tide
       Station Latitude Longitude Range
Range Level Predictions SAND ISLAND, MIDWAY
ISLANDS 28 12.7' 177 21.6' 0.8 1.2 0.6
Predictions Laysan Island 25 46' 171 45' 0.7
1.0 0.4 Predictions East Island, French Frigate
Shoals 23 47' 166 13' 0.9 1.4 0.6 Predictions
Nonopapa, Niihau Island 21 52' 160 14' 1.0
1.6 0.7 Predictions Kauai Island Waimea Bay 21
57' 159 40' 1.0 1.6 0.7 Predictions Port
Allen, Hanapepe Bay 21 54' 159 35' 1.1 1.7 0.7
Predictions NAWILIWILI 21 57.4' 159 21.6'
Predictions Hanamaulu Bay 22 00' 159 20' 0.0
1.2 1.8 Predictions Hanalei Bay 22 13' 159
30' 1.3 1.8 0.8 Predictions Oahu Island
Haleiwa, Waialua Bay 21 36' 158 07' - - 1.6
0.7 Predictions Waianae 21 27' 158 12' 1.2
1.8 0.8 Predictions HONOLULU 21 18' 157 52'
1.3 2.0 0.8 Predictions Hanauma Bay 21 17'
157 42' 1.3 1.9 0.8 Predictions Waimanalo 21
20' 157 42' 1.1 1.8 0.8 Predictions MOKUOLOE
21 26.2' 157 47.6' 1.2 2.0 1.0 Predictions
Waikane, Kaneohe Bay 21 30' 157 51' 1.4 2.2
1.1 Predictions
22
Inquiry

• Which has the greatest tidal effect sun or moon?
• Where is the greatest tidal range located?
• Which lunar phase produces moderate tides?
• How is a tidal bore created?