Chapter 16 Section 2 Waves and Tides The Dynamic Ocean Chapter 16 Section 2 Waves and Tides

Chapter 16-2 Overview From where do ocean waves obtain their energy? What three factors affect the characteristics of a wave? How does energy move through a wave? What causes tides?

So what are waves???? They obtain their energy and motion from wind.

Anatomy of a Wave Crest The tops of the waves Trough The bottom of the waves

Anatomy of a Wave Picture

Wave Characteristics Wave height The vertical distance between the trough and crest Wavelength The horizontal distance between two successive crests OR two successive troughs Wave period The time it takes one full wave (wavelength) to pass a fixed position

Wave characteristics are dependent on three factors: Wind speed Length of time wind has blown Fetch Distance the wind traveled across open water

Wave Motion Waves travel great distances. The water does not travel the entire distance, but the wave does. Consider the following: a floating object on the water such as a rubber duck Disturb the water creating a wave What motion does the duck exhibit? (Forward motion or up and down or both – Explain)

Water particle movement diagram

So what is the true motion of water particles? Circular orbital motion, see pictures on page 456 and 457 It allows energy to travel forward yet the individual water particles only move in a circle

Breaking Waves continued As the original wave advances toward shore: It begins to “feel bottom” at a water depth = ½ of its wavelength

Tides Daily change in the elevation of the ocean surface. Ocean tides result from the change in the gravitational attraction exerted upon Earth by the moon and the sun.

Ocean Tides The moon is the primary body influencing ocean tides It takes the moon 29 ½ days to make one revolution around the Earth The sun is farther away and only has about 46% of the moon’s effect

So how does this gravitational force work? Consider tug of war between two teams – the Earth & the moon The moon is pulling on the Earth’s water bodies that are closest to it --- this creates a bulge on the side closest to the moon Therefore, the side farthest from the moon has less pull

So what does it look like? When the “bulge” is the greatest, we see a high tide When the pull is not great, we see a low tide The moon makes a revolution around the Earth, but the Earth is rotating which changes its position of the pull from the moon Water moves toward the pull giving the high tide where the pull is greatest and low tide where the pull is the least strong Most coastal locations will see 2 high tides and 2 low tides each day

Tidal Cycle The sun has some influence on tidal bulges Its influence is most noticed at full and new moons as they sun and moon are aligned Alignment = combined forces pulling on the Earth’s water Larger tidal bulges (higher hide tides) are created as are larger tidal troughs (lower low tides)

Tidal Cycle

Tidal range Difference in height between successive high and low tides Spring tides Tides having the greatest tidal range due to the alignment of the Earth, moon & sun Experienced during full and new moons 2 per month Neap tides When the daily tidal range is the least Experienced at the first and third quarters of the moon (when the moon and sun act on Earth at right angles) See figure 13, page 459

Tidal Patterns Three main tidal patterns: Diurnal tides Semidiurnal tides Mixed tides

Diurnal tides A single high tide & a single low tide each day Typical near Gulf of Mexico Semidiurnal tides each day Two high and two low tides Highs are similar in height as are the lows Common along the Atlantic coast of U. S. Mixed tides Similar to semidiurnal pattern BUT Large inequality in high water heights and/or low water heights Common along Pacific Coast of U. S. and other parts of world