Download Ocean Ch # 9 Tides

☰





Search
Explore
Log in
Create new account
Upload
×
MAY 2011
Oceanography Ch # 9.
TIDES
The periodic rising and falling of the average Sea Level. Tides are regular,
very long, thousands
of miles , shallow water waves, , max 50 ft. high.
First explained by Newton. The Universal Law of Gravitation – every particle of
mass attracts
every other particle in the Universe.
9 – 1. Causes of Tides.
Tides are generated by forces imposed on the earth by the Sun and the Moon
(gravitational
attraction). The resultant force (difference between the Gravitational and
Centripetal) causes
tidal bulges on earth, and generates the tides. Gravitational and centripetal
forces keep the
planet in orbit.
Tidal Bulges.
As a result of primarily the Moon’s gravity pull, there are two bulges on
opposite sides of the
earth, around the equatorial region. Most places should experience two hi tides
every 12 hr and
25 mins, based on the lunar day (24 hs and 50 mins).
Solar effect. – bulges are much smaller than the lunar bulges. (distance from
the earth and size
of the sun)
Earth’s rotational effect - as the earth spins, locations move in and out of the
tidal bulges. The
max tide is called the Flood tide (Spring) and the lowest tide is the Ebb tide.
9 – 2. How Tides vary during the monthly tidal cycle
The monthly cycle is 29.5 days. (how long it takes for the moon to go around the
earth). There
are 4 phases during the monthly cycle, namely:

New Moon – moon is located between the sun and earth.

First and 2nd. Quarters – A line drawn from the moon to the earth, and one from
the
sun to the earth form a right angle.

Full Moon - Earth is located between the sun and the moon.
When gravitational forces are lined up, the forces are added to each other
(Constructive) and
tides are very high. (Spring Tide) The opposite is Neap tide when the forces are
destructive.
Complicating Factors are:

Declination of the Moon and Sun.

Orbits are elliptical. Distance varies by 2.5% The max tide occurs when earth is
closest to the Sun (Perihelion) and closest to the moon. 92.2 Mmiles – 94.5 M
miles.
January each year.

Earth’s tilted axis 23.5 Deg

Moon’s orbit relative to the earth is 28.5 Deg. Its tilt is 5. Deg. Elliptical
orbit.
Variation is 8%. (375,000 km –Perigee, to 405,000 km- Apogee)
Effects of Elliptical Orbits. Earth’s distance from the Sun varies 2.5%. The max
tide occurs when
earth is closest (Perihelion and Perigee resp.) to the Sun and to the Moon.
Predicting Tides. The declination of the Moon determines the position of the
Tidal Bulges,
directly over the 28 Deg N or S Latitudes.
9 – 3. Tides in the Ocean.
Tidal bulges are 20,000 km apart – one half the earth’s circumference. The wave
speed is
affected by depth. Ocean avg. depth is 3.6 km. To be free of interference, depth
must be in xs
of 22 km.
The tide breaks up into units – Cells, the center of each is called the
AMPHIDROMIC point. The
crest and trough of the wave (tide) rotate around the amphidromic point. A line
joining points
where the tides are the same height, is called a COTIDAL LINE. In the Northern
hemisphere,
waves rotate clockwise. A complete rotation occurs once during a tidal period –
12 hrs.
Continental effects. They interrupt free movement of the bulges. Their location
and shape of
coastlines modify the waves. Other factors are sea floor topography, and water
temperature.
In addition, there are more than 400 other factors. A mathematical model is used
to determine
the exact time of the tides.
Types of Tidal Patterns.
Theory: Should be 2 highs and 2 lows (tides) every day. In reality, there are
three patterns,
which depend on location.
Diurnal - GOM ; SE Asia. 1 High and 1 Low tide daily
Semi diurnal – Atlantic US Coast. Two high and two low tides
Mixed Tidal Pattern – Pacific NA Coast. The most common in the world. Successive
high tides
have significantly different heights.
9 – 5. Tidal Phenomena in Coastal Regions.
When tides enter coastal waters, they are subjected to



Reflection
Amplification. – Can produce a standing wave phenomenon
Large lakes and Rivers also experience tidal phenomenon. Tidal bores affect
ecosystems
and their inhabitants. An extreme example is: The Bay of Fundy. It has the
largest tidal
range (17 meters).
Coastal Tidal Currents.
Currents that accompany the slow turning wave crest in the Northern Hemisphere
basins rotate
counter-clockwise and produce a Rotary Current. Friction increases in the
shallow water, and
the rotary current changes to a reversing current. These latter currents are
common at the
mouth of bays.
Whirlpools
A rapidly spinning body of water. A vortex occurs in shallow passages connecting
two large
bodies of water, that have different tidal cycles. Flow rates 10 – 16 km/hr. Ex:
the Maelstrom
on the west coast of the arctic Norway.
9 – 6. Can Tidal Power be Harnessed as a source of Energy?
Boston in the 17th and 18th. Century
To generate Power – initially more expensive than Oil or Gas plants. Drawbacks –
Harm to wild
life
Rance River , one of few operating Tidal Power plants in the world.
Download
1. Science
2. Earth Science
3. Oceanography
Ocean Ch # 9 Tides.doc
Chapter 10: Tides Fig. 10-6 Fig. 10-7
Tides
Powerpoint
Chapter 9: Tides
Tides
chapter 10
R Topic 17 notes - The University of West Georgia
class handout
Tides
lecture notes
Where did the term “lunacy” come from?
Chapter 8 Tides
Tides
studylib © 2017
DMCA Report