FAQ-Dynamics

1. Why are there usually two tides a day?

Imagine a girl swinging a five gallon bucket of water around her in a circle. Is she able to stand perfectly upright as she swings it around? No, she has to lean back to avoid falling over. She is pulling the bucket towards her and the bucket is pulling her forward, toward the bucket. What does this have to do with anything? Although the moon circles the earth approximately ONCE a day (Actually, the moon orbits the earth about every 27 days, but the earth revolves every day), at any given time there are TWO bulges of water (high tides) on the earth. Imagine this: the bucket is the moon, the girl is the earth, the energy she exerts to hang onto the bucket as she spins is gravity, her arms represent one high tide, and her long hair-flying out behind her as she spins-represents another high tide on the other side of the earth. Do you see it? The bucket is pulling her arms away from her towards the bucket, and because she's leaning back and spinning around, her hair is flying out behind her. So for every one time the bucket goes around her, we see two tides cycles. From http://wiki.answers.com/Q/Why_are_there_two_high_tides_and_two_low_tides_in_a_day

2. What are some of the differences between viscous and turbulent stresses?
3. Distinguish between hydrostatic (quasi-hydrostatic) and dynamic pressure.
4. Consider a meddy at mid depth in the water column. Outside of the meddy, the ocean is composed to two layers with densities , with the boundary between the layers at the midline of the meddy. The meddy has a density of . Assuming hydrostatic balance, sketch the hydrostatic pressures of the water column as a function of depth inside and outside the meddy.
5. In words or equations state the balancing terms in the equations of motion for:
a. Geostrophic flow
b. Quasi-geostrophic flow
c. Inertial motion
d. Ekman flow
6. Distinguish between barotropic and baroclinic motion.
7. Explain the differences between hindcast, nowcast, and forecast models.

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