Tides

Question 1

Tides are highest when the moon is…

The moon-earth system, revolving around…
with a period of

Answer 1

Tides are highest when the moon is…… new or full.

The moon-earth system, revolving around …a common centre of mass with a period of … 27,3 days

Question 2

1. Discuss how the moon creates two high tides and two low tides a day according to the equilibrium tide theory? Why is the M2 period 12.42 hrs long?

Answer 2

The tide theory is developed from Newton’s theory of gravitation, and consists of 2 symmetric tidal bulges, directly under and directly opposite the moon or sun. In this case(M2) it is the gravitational pull from the moon which makes the two tidal-waves. Since the moon has moved a bit during the cycle, one has to add 0.42 to the period.

Question 3

What is the equilibrium tide theory? Which assumptions does this theory have? And who developed it?

Answer 3

The eq. tidal therory was developed by Newton, and is based upon Newton’s 2. law (gravitation).

F = G•(M₁M₂)/R²

G= g\gravitational constant
M1 = mass 1, M2= mass 2 
R<sup>2</sup>= radius between the two objects

Assumptions: that there is no continents, and no boundaries.

Question 4

2.Discuss how the sun creates two high tides and two low tides s day according to the equilibrium tide theory?
Why is the S2 period is 12.00 hrs long?

Answer 4

The tide theory is developed from Newton’s theory of gravitation, and consists of 2 symmetric tidal bulges, directly under and directly opposite the moon or sun. In this case(S2) it is the gravitational pull from the sun which make the two tidal-waves.
Since the sun does not move during the period, one can divide the period 24hrs/2 cycles = 12 hrs/cycle.

Question 5

3.What is spring tide and why does it occur during new- and full moon?

Answer 5

Spring tide: when the moon, earth and sun is aligned, then the tides is a result of the tidas forces from both the moon and the sun. It does not matter if the moon and sun is aligned at the same side, since you get the same effect, just on the tidal-wave on the opposite side of the earth. That’s why the spring tide occur both during the new- and full moon.

Question 6

4.What is a neap tide? Why does neap tide occur during half-moon?

Answer 6

When the moon is 90 degrees to the sun, the gravitational forces from the moon and the sun starts to interfere and weaken each other. They result in a weaker tide called neap tide. The moon and sun is 90 degrees during half-moon (twice a month).

Question 7

Is it the sun or the moon that has the strongest gravitational pull on the water (and therefor having the strongest impact on the tides)?

Answer 7

Even tho the sun is much bigger then the moon, since the reduction of gravitational force weakens quickly with distance, it is therefore the moon which has the biggest gravitational pull - the tidal forces from the moon are aprox. twice the value of the sun

Question 8

What is the length of the period the moon needs to orbit the earth?

Answer 8

2 * 12,42 = 24,84 hours

Question 9

The moon orbits the earth in an elliptical path. Where is it during apogee?

Question 10

The moon orbits the earth in an elliptical path. Where is it during perigee?

Answer 10

Maximum tidal acceleration will occur when the moon is closest to the earth., AKA perigee

Question 11

What is perigee spring tide?

What is apogee neap tide?

Answer 11

When the moon is closest to the earth during its elliptical orbit(perigee), the spring tide will be bigger than normal.

When the moon is furthest from the earth during its elliptical orbit(apogee), the neap tide is less then usual.

Question 12

What is storm tide?

Answer 12

Spring tide + low pressure system+ wind

Question 13

What is a Kelvin wave?
How does it travel?
Can you draw the form of a Kelvin wave?

Answer 13

A kelvin wave is a wave in the ocean or the atmosphere that balance the Coriolis force up against topographic limits (a coastline ect)

700km per hour, around the adrospheric points along the right coastline.

Long wave, cylonic motion on the NH, can meet at the equator

Question 14

What is tides?

How does the tidal currents look like, and how is it connected to the speed of the tides?

Answer 14

Tides are the periodic rise and fall of the sea caused by the gravitational pull of the moon and the sun on the Earth
Tides are observed as long periodic waves, that is affected by the .and landmasses.

The tidal currents in open water are generally rotating, either cyclonic or anticyclonic. The current vector forms as an ellipse, with major-axis and minor-axis. The major axis represents the maximum current velocity and the minor axis the lower tidal velocity.

Question 15

What is the age of the tide?

Answer 15

There is a delay of the astronomical and the observed tide, meaning that the
The spring and the neap cycle occur normally some days after the full/new moon (or the half moon)
This is caused by friction and batymetry. This delay is called the age of the tide, and is usually around two days.

Question 16

Explain the different tidal components

Answer 16

N2: component that takes into the account that the moons orbit around the earth is elliptical.

K1: takes the declanation of the moon relative to the equiatorial plane into consideration

In addition there is to shallow water components, M6 and 2MN6

M6 is an amplification of M2

2MN6 an amplification of both M2 and N2

Question 17

Where are the tides the Strongest in the world? And why?

Answer 17

The Bay of Fundy in Novia Scotia.

Fundy’s tides are the highest in the world because of an unusual combination of factors: resonance and the shape of the bay.

The water in the Bay of Fundy has a natural resonance or rocking motion called seiche. You could compare this to the movement of water in a bathtub. Although the water in a bathtub sloshes from one end to the other and back again in a few seconds, it takes about 13 hours for the water in the bay to rock from the mouth of the bay to the head of the bay and back again. As the ocean tide rises and floods into the bay every 12 hours and 25 minutes, it reinforces the rocking motion.

The bay’s shape and bottom topography are secondary factors contributing to Fundy’s high tides. The bay becomes narrower and shallower — from 130 m (426′) to 40 m (131′) — toward the upper bay, forcing the water higher up onto the shores.