Tides Tides Are the Longest of All Ocean Waves hence they are Long waves Tides Are Forced Waves Formed by Gravity and Inertia They are responsible for the rise and fall in sea level Tides ID: 231050
Download Presentation The PPT/PDF document "Chapter 11 Tides" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Chapter 11 TidesSlide2
Tides
Tides Are the Longest of All Ocean
Waves, hence they are
Long waves
Tides Are Forced Waves Formed by Gravity and InertiaThey are responsible for the rise and fall in sea level.Slide3
Tides
occur as shallow water waves
and depend heavily upon topography.
One low-tide/high-tide cycle takes about 12
hrs and 25 min.Tidal range is the difference in ocean level between high-tide and low-tideSlide4
What is the Tidal Range?
HT = 30 ft, LT = 20 ft
HT = 20 ft, LT = 12 ft
HT = 50 ft, LT = 20 ft
2 high tides = flood tides
2 low tides = ebb tides
each daySlide5
The gravitational attractions of
the Moon and Sun
acting on the rotating Earth.
What Causes TidesSlide6
Tides
Tides result from the gravitational pull of the moon and, to a lesser degree, the sun.Slide7
Gravity and inertia
A planet orbits the sun in balance between gravity and inertia. (a) If the planet is not moving, gravity will pull it into the sun. (
b
) If the planet is moving, the inertia of the planet will keep it moving in a straight line. (
c
) In a stable orbit, gravity and inertia together cause the planet to travel in a fixed path around the sun.Slide8
The moon’s gravity
pulls
the ocean toward it. The motion of Earth around the center of mass of the Earth-moon system
causes
a bulge on the side of Earth opposite the moon. The combination of the two effects creates two tidal bulges.
Tidal bulgesSlide9
Gravitational Effect of the Moon
Two big bulges of water form on the Earth:
one directly under the moon
another on the exact opposite side
As the Earth spins, the bulges follow the moon.Slide10
Tidal bulges
follow the moon. When the moon’s position is north of the equator, the gravitational bulge toward the moon is also located north of the equator and the opposite inertia bulge is below the equator.
Lunar tidal bulgeSlide11
Sun and Moon Influence Tides Together
Relative positions of the sun, moon, and Earth during spring and neap tides. (a) At the new and full moons, the solar and lunar tides reinforce each other, making
spring
tides
. (b) At the first-and third-quarter moons, the sun, Earth, and moon form a right angle, creating neap tides.Slide12
Spring tides
When the sun and the moon are aligned, their gravitational effects combine to increase the planetary water bulge.Slide13
Gravitational Effect of the Sun and Moon
Spring Tides -
every 2 weeks
Earth, Moon, and Sun are lined up
High Tides
~20% higher than normal
Low Tides are lower than normalSlide14
Neap tides
When the moon and sun are at right angles (quarter moon stages), tides are weaker = neap tides.Slide15
Gravitational Effect of the Sun and Moon
Neap
Tides
-
every 2 weeks
Earth, Moon, and Sun
form right angles
High Tides are
~20% lower than normal
and Low Tides are higher than
normal, opposite interval to Spring TideSlide16
Tidal records for a typical month at (a) New York and (b) Port Adelaide, Australia. Note the relationship of spring and neap tides to the phases of the moon.
Sun and Moon Influence Tides TogetherSlide17
The magnitude of tides varies
Spring tide - higher
high and lower low
tides (more extreme)
Neap tide - weaker tideTiming of spring and neap tides are important
for
forecasting
hurricane storm surge – why?Slide18
NOAA tide demonstration
http://www.montereyinstitute.org/noaa/lesson10.html
Ignite learning mediaSlide19
The Dynamic Theory of Tides
The
dynamic theory of tides
explains the characteristics of ocean tides based on celestial mechanics (the gravity of the sun and moon acting on Earth) and the characteristics of fluid motion.
Semidiurnal tides occur twice in a lunar day
Diurnal tides
occur once each lunar day
Mixed tides describe a tidal pattern of significantly different heights through the cycleAmphidromic points are nodes at the center of ocean basins; these are no-tide points.Slide20
Diurnal
One high and one low tide each lunar day
Semidiurnal
Two high and two low tides of about the same height daily
Tidal patternsSlide21
Tidal
Patterns of world coastlines
Common tide types.
A mixed tide pattern at Los Angeles, California.
A diurnal tide pattern at Mobile, Alabama.
A semidiurnal tide pattern at Cape Cod, Massachusetts.
The worldwide geographical distribution of the three tidal patterns. Most of the world’s ocean coasts have semidiurnal tides.Slide22
Co-tidal map shows tides rotate around
amphidromic
points. vertical movement)
There are 140
amphidromic points in the world’s oceans.
More down-to-earth pattern of tides in the ocean
Tides in the Ocean
Amphidromic
PointsSlide23
Tidal Ranges increase with increasing distance from
Amphidromatic
points
.
Coriolis
drives the process counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere.
Red = most extreme Blue = least extreme
White lines indicate tide waves that circulate around these points due to Coriolis.Slide24
Tidal currents occur in some bays and rivers due to a change in tides
Ebb currents
- produced by outgoing tides
Flood currents
- produced by incoming tide
LSW
means Lower Slack Water
HSW
means Higher Slack Water
Tidal Currents