4 Basic Forces and Tides

Question 1

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

Answer 1

gravity
pressure gradient forces
friction

Question 2

which way doas pressure gradient force go

Answer 2

from high pressure to low pressure

Question 3

what two ways does friction act on the ocean basically

Answer 3

slows down fast moving fluid
speeds up the slow moving fluid

Question 4

what causes apparent forces?

Answer 4

non-inertial frames of reference

Question 5

what are the units and direction of centrifugal force?

Answer 5

N/m^3, away from axis of rotation

Question 6

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

Answer 6

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

Question 7

do we consider centrifugal force in balance equations?

Answer 7

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

Question 8

what is the coriolis force?

Answer 8

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

Question 9

what axis msut be consider for the coriolis force?

Answer 9

the local axis, not where the axis is

Question 10

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

Answer 10

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

Question 11

what does f* represent?

Answer 11

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

Question 12

what does f represent?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

how does f act on the horizontal plane?

Answer 14

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

Question 15

where is f negative?

Answer 15

the southern hemisphere

Question 16

what name does f have?

Answer 16

coriolis parameter

Question 17

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

Answer 17

circles
inertial oscillations

Question 18

what drives horizontal flow in the ocean surface?

Answer 18

friction
coriolis
net force of acceleration

Question 19

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

Answer 19

mainly:
coriolis
horizontal pressure gradient

Question 20

what is geostrophic balance?

Answer 20

balance between the pressure gradient force and Coriolis force

Question 21

what is geostrophic velocity?

Answer 21

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

Question 22

isobars definition

Answer 22

lines on maps of constant pressure

Question 23

where is the horizontal pressure gradient relative to isobars?

Answer 23

perpendicular from high to low pressure

Question 24

what determines the magnitude of the horizontal pressure gradient?

Answer 24

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

Question 25

what is the geostrophic flow?

Answer 25

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

Question 26

which side is coriolis on in the northern hemisphere?

Answer 26

right

Question 27

which side is coriolis on in the southern hemisphere?

Answer 27

left

Question 28

where is the geostrophic flow relative to isobars?

Answer 28

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

Question 29

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

Answer 29

tide generating force

Question 30

what is TGF

Answer 30

tide generating force

Question 31

what balances tide generating force?

Answer 31

local accelerations coriolis and pressure gradient is too small comparatively

Question 32

what causes the tides?

Answer 32

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

Question 33

how many tidal bulges and dips are there?

Answer 33

two each

Question 34

what is a sidereal month and how long is it?

Answer 34

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

Question 35

what is the residual force?

Answer 35

the tide generating force fgrav - Fcentri = TGF

Question 36

where is the residual force balanced?

Answer 36

at the earth's center of mass

Question 37

what is the zenith?

Answer 37

point on earth directly under the moon

Question 38

what is the nadir?

Answer 38

spot directly across the earth from the zenith

Question 39

how often do the tides repeat? why

Answer 39

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

Question 40

how long is a lunar day

Answer 40

24.9 hours

Question 41

what is diurnal inequality?

Answer 41

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

Question 42

what causes diurnal inequality?

Answer 42

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

Question 43

what is the tropic/equatorial cycle?

Answer 43

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

Question 44

what is the perigean/anomalistic cycle?

Answer 44

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

Question 45

what are spring tides

Answer 45

strong tides from moon and sun TGF adding together

Question 46

what are neap tides

Answer 46

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

Question 47

what moons are seen at spring tides?

Answer 47

full and new

Question 48

what moons are seen at neap tides?

Answer 48

first and second quarter

Question 49

how long is the sydonic month? why?

Answer 49

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

Question 50

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

Answer 50

2 each

Question 51

why do we need a more dynamic theory for tides?

Answer 51

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

Question 52

what is the M2 tide?

Answer 52

semi diurnal consituant with a period of 12.4 hours

Question 53

what is the K1 tide?

Answer 53

diurnal constituent with period of 23.9 hours

Question 54

what causes tides to be elliptical?

Answer 54

coriolis effects

Question 55

what happens to the tide in narrow shallow water?

Answer 55

tide moves quicker because of mass conservation

Question 56

what happens when we have stronger/faster tides?

Answer 56

more mixing occurs

Question 57

what is a tidal mixing front

Answer 57

point where stratification is destroyed by mixing