Chapter 10 Waves

Wave Formation Generating Force Restoring Force Surface tension Gravity

Wave Formation Gravity waves Generating Force Wind Ripples Capillary waves Cat’s-paws

Anatomy of a Wave Crest Trough Wavelength (L) Wave height (H) Amplitude = 1/2H Period (T) Seconds/cycle Frequency Cycles/second

Wave Motion As waves pass, wave form and wave energy move rapidly forward, not the water! Two basic motions associated with waves: Forward motion Orbital motion

Orbital Motion As wave approaches, a water particle will trace a circular path Diameter of orbit at surface = wave height

Wave Base Wave particle orbits are not detectable below ~1/2 wavelength

Wave Speed Celerity (C) Period remains the same C = wavelength/period C = L/T Period remains the same

Wave Measurement The simplest technique is to examine the oscillation of waves against a pole fixed marked in meters Oceanographers will employ pressure sensors anchored to the sea floor

Wave Measurement Satellite Imagery

Deep-water Waves Waves that propagate in water than is one-half their wavelength Wave base is above the sea floor

Deep-water Waves L = (g/2π)T2 L = (1.56 m/sec2)T2 L/T = (1.56 m/sec2)T C2 = 1.56L

Storm Centers Progressive wind waves (PWW’s) Wind Gravity Propagate in particular direction

Storm Centers Progressive wind waves (PWW’s) Confused seas Forced waves

Dispersion Free waves No longer wind-driven waves Period does not change

Group Speed Wave Train Group Speed (V) One-half the wave velocity for deep-water waves V = C/2

Constructive Wave Interference Crests & troughs coincide Build up of crest & deepening of trough

Destructive Wave Interference Crest of one wave coincides with trough of another wave (and vice versa) Dampening of wave

Wave Height The variety and size of wave generated depends on 3 factors: Speed of the wind How long the wind blows Size of the fetch of the wind

Wave Height 40-50o S Typical maximum fetch Ideal wave production No landmasses to limit fetch Westerlies Typical maximum fetch 920 km (500 miles)

Wave Height Larger waves will be produced on the side of the storm where the winds are blowing in the same direction as the storm is moving 10-15 m (33-49 ft) 100-200 m (330-660 ft) long

Wave Height Episodic waves Produced as a result of constructive interference Occur most often near edge of continental shelf 20-30 m 50 knots