tides & currents

Question 1

why does the moon and sun look the same size to us

Answer 1

Moon = small, Sun = further away

Question 2

how does the moon move in a circular orbit around the earth

Answer 2

Earth has gravitational pull on moon, moon has gravitational pull on earth - but moon is trying to move in a straight line

Question 3

how many days does it take for moon to go around the earth + earth to spin around sun

Answer 3

27 days for moon to go around the earth
365 days for earth to spin around sun

Question 4

why isn’t the centre of gravity centered on the planet

Answer 4

The gravitational pull of the earth on the moon and moon on the earth mean its slightly off to one side towards where the moon is

Question 5

what causes high tides

Answer 5

the fact the centre of gravity is slightly to one side where the moon is also affects the oceans – water gets sucked to the same side as the moon (gravitational bulge)

Question 6

what’s the Gravitational force equation (F)

Answer 6

G m1 x m2
————–
r2
- m1, m2 = Mas of earth and moon
- r2 = distance between the two

Question 7

explain why distance (r2) affects gravitational pull (F)

Answer 7

• The further away you are from something that has a gravitational pull, the quicker the gravitational pull is going to drop off from it
• Means there will be a strong gravitational pull on the right side of the planet (smaller distance) - water being pulled towards the moon
• pull on the other side of the planet is smaller - water is dropping away from the moon
• This is what gives us a bulge on either side of the planet

Question 8

how do tides change

Answer 8

go up and down sinusoidally – they change more slowly at high or low water + change more rapid in the middle of the tide e.g. 3hrs after high water

Question 9

how can we predict tides

Answer 9

• earth rotates once every 24 hours, which should give a tidal cycle every 12 hours
• BUT the moon orbits once every 27 days, which moves to tide forward ~1 hour a day - So the tide cycles approximately every 12 hours and 25 minutes

Question 10

why does the moon have more than twice the influence the sun has on tides

Answer 10

its closer to earth

Question 11

2 components of tidal force

Answer 11

• the pull of the moon sucking the water
• the earth sucking it back

Question 12

what are spring tides and why does it happen

Answer 12

• Tidal range is at its biggest – biggest high waters + lowest low waters
• Happens because sun + moon are in line – pulling in the same direction

Question 13

what are neap tides and why does it happen

Answer 13

• Smallest change in tidal heights
• 90 degrees – moon is in opposite direction to the sun - Sun is pulling to one side, moon pulling to the other

Question 14

over how many days do we get 2 sets of both tide types

Answer 14

Over 27 days

Question 15

what kind of tide does full moon an half moon tie in with

Answer 15

Full moon = spring tides
Half moon = neap tides

Question 16

what would happen to tides If there was no land masses or seabeds

Answer 16

a tidal bulge with a frequency of 2 cycles per day would continue around the earth

Question 17

how does land affect tidal ranges

Answer 17

• there is an interaction between land and the energy of the tidal bulge – waves reflect and refract as they hit land
• This in combination with coriolis results in interference patterns – can both increase + ameliorate tidal range

Question 18

what are Amphidromic points

Answer 18

Where interference completely cancels tidal movement out - no tidal variation

Question 19

how can Coastal morphology affect tidal range

Answer 19

e.g. esturines, can affect tidal range by increasing or decreasing it - compresses energy and results in water pushing up

Question 20

what are Coriolis forces and what does it result in

Answer 20

• to do with Earth’s rotation
• When an object travels across latitudes, the inertia causes deflection to the trajectory
• So…..because planet rotates west to east:
  In N. Hemisphere: object deflects to right
  In S. Hemisphere: object deflects to left

Question 21

what’s the Major driving force of SURFACE ocean circulation

Answer 21

wind

Question 22

what’s the Major driving force of ATMOSPHERIC circulation

Answer 22

solar energy

Question 23

why is Heat distribution uneven across Earth’s surface

Answer 23

Warm air rises (less dense); cold air sinks

Question 24

what does Hadley’s model of atmospheric circulation show

Answer 24

• Planet is warm in the equator (tropics)
• The hot air in these areas will rise (less dense) - to replace this air it is taken from the sides (from north to south)
• But air movement is modified by Coriolis effect – means there are 3 cells in each hemisphere instead of one just going from north to south

Question 25

what effects the air movement

Answer 25

• Coriolis effect
• means there are 3 cells in each hemisphere instead of one just going from north to south
• as air flows from high pressure zone to low pressure zone, its trajectory is modified by Earth’s rotation

Question 26

apart from wind, what are the ocean circulation patterns further modified by

Answer 26

 Coriolis effect
 Pressure gradient
 Presence of landmass

Question 27

what keeps surface water moving for a period of time even after the winds have stopped

Answer 27

Inertia - Surface ocean circulation thus responds more to average atmospheric circulation than to short term weather changes

Question 28

how is the ocean circulation patterns deflected by Coriolis effect

Answer 28

Because of small frictional coupling between air and water

Question 29

what is ekman motion

Answer 29

Interaction of wind + coriolis effect
- Deflects the movement of water to the right – net movement = 90degrees to the direction or the wind

Question 30

what is the product of Coriolis force combined with Ekman transport

Answer 30

large, cyclical currents in the north and south hemispheres (subtropicl gyres)
- Warm, nutrient poor water is piled up into the centre of these gyre systems - marine deserts

Question 31

what are the largest surface water currents on the planet

Answer 31

subtropical gyres in the north and south hemispheres

Question 32

what areas do Tropical organisms and cold loving organisms extend into

Answer 32

• Tropical organisms e.g. corals extend into higher latitudes on the western side of the oceans
• Cold loving organisms e.g. kelp extend into lower latitudes on the eastern side of the oceans

Question 33

what are Coastal upwellings

Answer 33

• Southern hemisphere
• Wind comes down the coast from north -> south – pushes the surface waters this way
• Ekman transfer pushes this water 90degrees on average to the right of the wind direction (offshore)
• The cold nutrient-rich water underneath rises up to replace the water that has moved – results in coastal upwellings