- Slides: 24
Chapter 11 Tides
Tides • Tides Are the _________________, hence they are ____ waves • Tides Are Forced Waves Formed by _____ and ______. • They are responsible for the ______ and _______ in sea level.
• Tides occur as ______ waves and depend heavily upon __________. • _______ low-tide/high-tide cycle takes about _________. • ________ is the difference in ocean level between _____ and ______
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 = _______ 2 low tides = ________ each day
What Causes Tides The gravitational attractions of ____________ acting on the rotating Earth.
Tides • Tides result from the ________ of the _______ and, to a lesser degree, the _______.
Gravity and inertia A planet orbits the sun in _____ between _____ and ______. (a) If the planet is not moving, gravity will pull it into the sun. (b) If the planet is moving, the _____ of the planet will __________ in a straight line. (c) In a stable orbit, gravity and inertia ______ cause the planet to travel in a _______ around the _____.
Tidal bulges The moon’s gravity _______ the ________ it. The motion of Earth around the center of mass of the Earth-moon system causes a ______ on the side of Earth ______ the moon. The combination of the two effects creates ____________.
Gravitational Effect of the Moon • _______ big _____ of water form on the Earth: – one _______ under the _____ – another on the ____________side • As the Earth spins, the bulges _____ the moon.
Lunar tidal bulge Tidal bulges follow the moon. When the moon’s position is _____ of the equator, the gravitational bulge _______ the moon is also located ________ of the equator and the _________ is ______ the equator.
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 ____________, making ________. (b) At the first-and third-quarter moons, the sun, Earth, and moon form a ______ angle, creating _________.
Spring tides • When the sun and the moon are ______, their gravitational _____combine to _______ the planetary water bulge.
Gravitational Effect of the Sun and Moon • Spring Tides -___________ – Earth, Moon, and Sun are _____ – _______~20% higher than normal – ______ are lower than normal
Neap tides • When the moon and sun are at _______ (quarter moon stages), tides are _____ = ____ tides.
Gravitational Effect of the Sun and Moon • Neap Tides- __________ – Earth, Moon, and Sun form _____ – High Tides are ~20% _______ than normal and – Low Tides are ____ than normal, opposite interval to Spring Tide
Sun and Moon Influence Tides Together 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.
The magnitude of tides varies • Spring tide - _______ high and _______ low tides (more extreme) • Neap tide - ______ tide • Timing of spring and neap tides are important forecasting hurricane storm surge – why?
NOAA tide demonstration • http: //www. montereyinstitute. org/noaa/lesson 10. html Ignite learning media
The Dynamic Theory of Tides • The _______________ 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 ______ in a lunar day • Diurnal tides occur _____ each lunar day • Mixed tides describe a tidal pattern of significantly _______ heights through the cycle • Amphidromic points are _____ at the _____ of ocean ______; these are no-tide points.
Tidal patterns • _________ high and one low tide each lunar day • _________ high and two low tides of about the same height daily •
Tidal Patterns of world coastlines Common tide types. (a) A mixed tide pattern at Los Angeles, California. (b) A diurnal tide pattern at Mobile, Alabama. (c) A semidiurnal tide pattern at Cape Cod, Massachusetts. (d) The worldwide geographical distribution of the three tidal patterns. Most of the world’s ocean coasts have semidiurnal tides.
Tides in the Ocean • 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 Amphidromic Points
Tidal ________ increase with increasing _______ from Amphidromatic points. _______ drives the process _________ in the northern hemisphere and ________ in the southern hemisphere. White lines indicate tide waves that circulate Red = most extreme around these points due to Coriolis. Blue = least extreme
Tidal Currents Tidal currents occur in some bays and rivers due to a change in tides – Ebb currents - produced by ______ tides – Flood currents - produced by ________ tide – LSW means _________ – HSW means _________