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EOSC 372 > 4 Basic Forces and Tides > Flashcards

4 Basic Forces and Tides Flashcards

1
Q

what ‘real’ forces can be found in the ocean?

A

gravity
pressure gradient forces
friction

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2
Q

which way doas pressure gradient force go

A

from high pressure to low pressure

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3
Q

what two ways does friction act on the ocean basically

A

slows down fast moving fluid
speeds up the slow moving fluid

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4
Q

what causes apparent forces?

A

non-inertial frames of reference

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5
Q

what are the units and direction of centrifugal force?

A

N/m^3, away from axis of rotation

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6
Q

since centrifugal force is dependent on distance from axis of rotation, what effect does this have on magnitude on earth?

A

largest at the equator, smallest at the poles
causes a bulge at the equator

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7
Q

do we consider centrifugal force in balance equations?

A

no, it is too tiny compared to gravity which is in the same direction

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8
Q

what is the coriolis force?

A

apparent force happening because of a rotating reference frame that makes movig in a stright look like we’re turning

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9
Q

what axis msut be consider for the coriolis force?

A

the local axis, not where the axis is

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10
Q

how do we label positive x,y,z as earth centric coordinates?

A

y = North
z = local up against gravity
x = east

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11
Q

what does f* represent?

A

the upwards directed force associated with the northwards vector component of coriolis force

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12
Q

what does f represent?

A

the southwards directed force associated with the upwards vector component of coriolis force

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13
Q

which component (f or f*) is important for ocean motions? why?

A

f, because f* upward force is dwarfed by gravitional force, it has no effect

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14
Q

how does f act on the horizontal plane?

A

acts on the tangent to the earth’s surface and is directed 90 degrees to the right of flow

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15
Q

where is f negative?

A

the southern hemisphere

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16
Q

what name does f have?

A

coriolis parameter

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17
Q

what shape do moving parcels make because of coriolis in the absence of other forces? what are they called?

A

circles
inertial oscillations

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18
Q

what drives horizontal flow in the ocean surface?

A

friction
coriolis
net force of acceleration

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19
Q

what drives horizontal flow in the ocean interior in the long term?

A

mainly:
coriolis
horizontal pressure gradient

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20
Q

what is geostrophic balance?

A

balance between the pressure gradient force and Coriolis force

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21
Q

what is geostrophic velocity?

A

velocity who’s associated coriolus force matches the pressure gradient force exactly

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22
Q

isobars definition

A

lines on maps of constant pressure

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23
Q

where is the horizontal pressure gradient relative to isobars?

A

perpendicular from high to low pressure

24
Q

what determines the magnitude of the horizontal pressure gradient?

A

how fast the pressure is changing
inversely proportional to distance between isobars

25
Q

what is the geostrophic flow?

A

flow occuring proportional to the coriolis force, which is always 90 degrees from it

26
Q

which side is coriolis on in the northern hemisphere?

A

right

27
Q

which side is coriolis on in the southern hemisphere?

A

left

28
Q

where is the geostrophic flow relative to isobars?

A

along the isobars to keep high pressure to the right/left

29
Q

what drives horizontal flow in the ocean interior in the short term?

A

tide generating force

30
Q

what is TGF

A

tide generating force

31
Q

what balances tide generating force?

A

local accelerations
coriolis and pressure gradient is too small comparatively

32
Q

what causes the tides?

A

gravitational attraction to the moon/sun
centripetal force larger than lunar gravity flung away

33
Q

how many tidal bulges and dips are there?

A

two each

34
Q

what is a sidereal month and how long is it?

A

rotation of the earth and moon arounf their joint center of mass
27.3 days

35
Q

what is the residual force?

A

the tide generating force
fgrav - Fcentri = TGF

36
Q

where is the residual force balanced?

A

at the earth’s center of mass

37
Q

what is the zenith?

A

point on earth directly under the moon

38
Q

what is the nadir?

A

spot directly across the earth from the zenith

39
Q

how often do the tides repeat? why

A

every 24.9 hours
moon and earth are rotating at the same time
in one day, the moon rotates 1/27.3 of it’s orbit, so the earth has to catch up

40
Q

how long is a lunar day

A

24.9 hours

41
Q

what is diurnal inequality?

A

presence of one more intense and one less intense low/high tide

42
Q

what causes diurnal inequality?

A

the moon is not directly above the equator because of the earth’s tilt

43
Q

what is the tropic/equatorial cycle?

A

two week long cycle where the moon becomes in line with the equator

44
Q

what is the perigean/anomalistic cycle?

A

27.3 day cycle where the moon is at one end of elliptical orbit in the northern or southern hemisphere

45
Q

what are spring tides

A

strong tides from moon and sun TGF adding together

46
Q

what are neap tides

A

weak tides caused by the moon and sun TGF working against each other

47
Q

what moons are seen at spring tides?

A

full and new

48
Q

what moons are seen at neap tides?

A

first and second quarter

49
Q

how long is the sydonic month? why?

A

29.5 days
because earth is also rotating around the sun, the moon has to move slightly farther to make up for the rotation

50
Q

how many spring/neap cycles occur in a sydonic month?

A

2 each

51
Q

why do we need a more dynamic theory for tides?

A

because technically the speed of the tides can’t keep up with the speed of the TGF

52
Q

what is the M2 tide?

A

semi diurnal consituant with a period of 12.4 hours

53
Q

what is the K1 tide?

A

diurnal constituent with period of 23.9 hours

54
Q

what causes tides to be elliptical?

A

coriolis effects

55
Q

what happens to the tide in narrow shallow water?

A

tide moves quicker because of mass conservation

56
Q

what happens when we have stronger/faster tides?

A

more mixing occurs

57
Q

what is a tidal mixing front

A

point where stratification is destroyed by mixing

EOSC 372 (5 decks)

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