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Midterm 1

Terms in this set (93)

Where is the warmest surface water found in the global ocean?
D: Both A and B.

A) in the Warm Pool
B) Equatorial Western Pacific
Where in the water column are potential and in-situ temperature the same?
D: at the surface
Of the three factors that influence water density, which one can oceanographers measure with the least accuracy?
Pressure
If the density of seawater is 1024.035 kg m^-3, what is sigma?
σ(s,t,p) = (ρ(s,t,p)) - 1000, 1024.035 - 1000 = 24.35 /m^3
What is the temperature range (deg. C.) of most (75%) seawater?
0 - 5 deg. C
What is the salinity range (ppt) of most (75%) seawater?
34 - 35 p.p.t
Is surface salinity higher in the equator or mid-latitudes (30 deg. N or S) ?
B: Mid-latitude
Which variable causes the largest water density changes in the ocean:
C: Pressure
What concentration defines oxygen deficient water (report the units)?
Oxygen Concentration < 0.2 ml O2 / Liter
Rank the following surfaces in order of decreasing albedo, by labelling them from 1 (highest albedo) to 4 (lowest albedo).
sea ice: 1
ocean: 4
forest: 3
desert: 2
Define salinity and chlorinity.
Salinity: Total dissolved g of salts in a kg solution. Major seawater chemistry dominated by Na+ and Cl- . Yet, other cations and anions are also important. The grams divided by kilogram, leads to units of parts per thousand (‰).
Chlorinity: Grams of Cl- (chloride) per kilogram of seawater. Assuming ratio of Cl- to salinity is constant, salinity can be estimated from chlorinity, as follows:
Salinity (‰) = 1.80655 * Clorinity (‰)
Write the Stephan-Boltzmann equation, explaining all the terms.
Stephan-Boltzman (S-B) relationship:
Watts / m^2 = E = σ e * k^4
σ = S-B constant 5.67 10^-8 W m^-2 k^-4
e = emissivity = 1 in ideal case
k^4 = Kelvin temperature to 4th power
Explain what are Oxygen Minimum Zones. For full credit, mention one place where they occur in the Pacific Ocean and the Indian Ocean, describe the depth range where they occur, and describe how they are linked to the processes at the sea surface.
The oxygen minimum zone (OMZ) is the zone in which oxygen saturation in seawater in the ocean is at its lowest, due to the high overlaying ocean productivity, the sinking of organic matter, and its oxidation at depth. This leads to the consumption of oxygen by respiration at depth, with the minimum occurring at depths of about 200 to 1,500 m (660-4,920 ft), depending on local circumstances.
The Eastern Tropical Pacific (equatorial Pacific Ocean) and the Bay of Bengal (tropical North Indian Ocean) are two areas with large OMZ.
NOTE: Traditionally, oxygen-deficient water is defined as having an oxygen ceoncentration < 0.2 ml O2 / Liter.
Explain the greenhouse effect. For full credit, describe how it affects the long-wave and the short-wave radiation flux through the atmosphere, (briefly) describe how it impacts the heat balance of the Earth, and mention the two main greenhouse gasses.
The process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without its atmosphere. Trapping of the sun's warmth in a planet's lower atmosphere, due to the greater transparency of the atmosphere to visible (short wave) radiation from the sun than to infrared (long wave) radiation emitted from the planet's surface. The trapping of the emitted longwave radiation alters the Earth's heat balance, by warming the ocean and the lower troposphere way above the equilibrium temperature - given the incoming short-wave radiation from the Sun.
The four most important greenhouse gasses are: water vapor and clouds, carbon dioxide, methane, and ozone.
Briefly describe what happened between March and Aug.
o Warming of water column
o Development of a seasonal thermocline (in May)
o Mixed layer develops in July
o Mixed layer warms (July - Aug.)
Briefly describe what happened between Aug. and March.
o First storms. Wind mixing deepens mixed layer (Aug. - Sept.)
o Heat moves deeper into water column (Aug. - Sept.)
o Mixed layer merges with seasonal thermocline (Sept. - Nov.)
o Mixed layer cools and deepens (Nov. - March)
What time of the year (months) does heat from the mixed layer move deeper into the water column?
From September to January. The mixed layer moves deeper, and the water below the mixed layer in one month is warmer in the following month.
What time of the year (months) does the deeper mixed layer occur? How deep is it?
The mixed layer is deepest in January - March, when it reaches below 100 m. In March the temperature profile is vertical from 100 m depth to the surface.
What time of the year (months) does a seasonal thermocline form? How deep is it?
Seasonal thermocline develops in May and a mixed layer develops in July. The seasonal thermocline disappears in Sept., when it merges with the mixed layer.
Overall, throughout the annual cycle, would you expect the net energy flux positive or negative at this site.
While the annual cycle (March to March) suggests there is no warming or cooling, because we return to the same cool mixed upper -water column (0 - 100 m deep), it is very likely that heat is moving into deeper water and contributing to the maintenance of the permanent thermocline (deeper than 100 m depth).
Globally, which latitudinal areas of the world have the largest seasonal variability in the temperature profile? Why?
Mid latitude (subpolar) regions (~ 50 deg. latitude) have the highest seasonal variability due to the strong seasonality in solar radiation (warming of the upper water column) and storminess (mixing the water column). Moreover, in areas with sea ice formation, this adds more variability with very cool winter conditions.
Globally, which latitudinal areas of the world have the smallest seasonal variability in the temperature profile? Why?
The tropics (latitude < 23 deg) in both hemispheres. These areas have little annual variability in solar radiation, and little seasonality in storms / wind patterns.
Globally, which latitudinal areas of the world have the largest seasonal variability in the mixed layer depth? Why?
Mid latitude (subpolar) regions (~ 50 deg. latitude), around the southern ocean and in the North Atlantic have the highest seasonal variability in mixed layer depth. In particular, areas where deep-water formation occurs can be mixed all the way to the bottom, down to 2000 m depth, in winter. In summer, these areas have high solar energy inputs and precipitation, which can lead to a very shallow (~ 10 m) mixed layer.
Globally, which latitudinal areas of the world have the smallest seasonal variability in the mixed layer depth? Why?
The tropics (latitude < 23 deg) in both hemispheres, have little annual variability in solar radiation, and little seasonality in storms / wind patterns. These are as have very smallow miwed layer depth (< 40 m).
Total Incoming Solar Radiation:
+342
Total Outgoing Radiation:
(-107) + (-235) = -342
Absorbed by Atmosphere:
+67
Absorbed by the Earth's surface:
+168 (SW) OR +324 (LW - Back Radiation)
Reflected Solar Radiation:
-107
Reflected by clouds, aerosols and atmospheric gasses:
-77
Reflected by the Earth's surface:
-30
Outgoing Longwave Radiation:
-235
Atmospheric Window:
-40
(Longwave) Surface radiation emitted by the Earth's surface:
-390
(Longwave) Radiation emitted by clouds:
-30
(Longwave) Radiation emitted by atmosphere:
-165
Latent heat from Earth's surface:
-78
Thermals:
-24
On average, how thick is the troposphere:
10 km
Where on Earth's surface is there a net surplus of heat from the Sun:
A: Tropics
Where on Earth's surface is there a net deficit of heat from the Sun:
B: Poles
As water pressure increases, sound travels:
A: faster in water
The latent heat of ice melting is ___ the latent heat of water evaporating:
B: Smaller than
If 1 degree of longitude covers 110 km at the equator, how much distance does it cover at 60 degrees N:
A: 55 km
How many subtropical Gyres are these in the world:
5

North and South Pacific, North and South Atlantic, and South Indian Oceans
How many subpolar Gyres are there in the world:
2

North Pacific and North Atlantic
How many deep-water formation locations are there in the world:
2

The North Atlantic and the Weddell Sea, in the Southern Ocean. However, there are two north Atlantic Sites: Labrador and Greenland Sea.
How many circumpolar currents are there in the world:
1

The circumpolar current flows eastward around Antarctica, at 60 deg. South.
Wind stress
o T (Tau) = Horizontal force of the wind on the sea surface, expressed as Newtons / m^2
o Work done by the wind on the ocean surface, defined as vertical transfer of horizontal momentum (mass * velocity) from the atmosphere to the ocean
o T = (Air Density) (Drag Coefficient) (Wind speed)^2
Coriolis Force
o Technically an apparent force - observed on objects moving on the surface of the rotating Earth. Yet, it is quantified and treated as a real force.
o Coriolis Force = CF = m u f
o Units of Force = Newtons (kg m s^-2 )
o m --- mass - units (kg)
o u --- velocity - units (m / sec)
o f --- Coriolis parameter = 2Ω*sin(latitude) Units of f = 1 / sec
o NOTE: Ω = Earth's angular momentum = (7.29 * 10^-5 radians/sec)
o Radians have no units
The Earth has a radius of 24,000 miles. What is its rotational speed at the equator?
o Radius = 24,000 miles
o Circumference = 2 pi 24,000 = 150,796 miles
o One Earth Rotation in 1 Day = Speed (miles / hour) = 150,796 / 24 = 6,283 miles / hour (mph)
What is the angular momentum of a 1-kg parcel of water at the equator?
o Radius = 24,000 miles
o Rotational Speed = 6,283 miles/hour
o Linear Momentum = 6,283 kg * miles/hour
o Angular Momentum = 150,792,000 kg miles miles/hour
The wind starts blowing over the ocean at rest. What is the magnitude of the force exerted by the wind when it accelerates a 2-kg parcel by 2 m/s^2 ?
o Force (units of Newtons) = Mass (kg) * Acceleration (m/s^2)
o Force = 2 kg * 2 m s^-2
o Force = 4 kg * m s^-2 = 4 Newtons
How much work is exerted when this force is applied on the water parcel for a distance of 1 km?
o Work (units of joules) = Force (Newtons) * meters (meters)
o Work = 4 Newtons * 1000 meters = 4000 joules
During a 2-hour rain storm, 10 liters of water were collected in a 0.5 m 2 tub. What was the water flux?
o Flux = the transfer of anything (in this case liters of water) per unit time (hours) and per unit area (meters squared).
o In this case, the rain flux = Flux of Rain = liters / (hours * meters^2 )
o Flux = 10 / (2 0.5) = 10 / 1 = 10 liters hours^-1 * meters^-2
Is water a "polar" or "nonpolar" molecule? Explain the reason and provide an example of how this property affects the physical properties of water.
The covalent bond makes water a polar molecule, because the electric charge is unevenly distributed between the two H atoms (positively charged) and the O atom (negatively charged). This asymmetry makes the water molecule a very good solvent. When water interacts with other polar molecules (like NaCl) it interferes with the forces bonding their atoms and dissolves them.
What molecular bonds allow water molecules to interact with each other? Explain what these bonds entail: what specific atoms are involved, and how many water molecules can one molecule interact with at once. Finally, provide an example of how this property affects the physical properties of water.
The hydrogen bonds (between H and O atoms in different water molecules), can link up to four adjacent water molecules. These intermolecular forces lead to high latent heat, high heat capacity, and high stickiness (viscosity). It also leads to high surface tension.
Define Heat capacity and report the values for air and water (for full credit show the units). Which one is higher? Briefly explain why?
Heat Capacity: The amount of heat energy that a substance can absorb, given a standardized mass and resulting increase in temperature (heating).
Water has the highest heat capacity on Earth.
Water: ~ 4200 J kg^-1 K^-1
Air: ~ 993 J kg^-1 K^-1
Note: The units of temperature can be degrees C or degrees K.
the light extinction coefficient, with units
I (z) = I (0) e^(-k z)
k = 0.196 (units: 1 / m)
the 1% light level in meters
I (z) = I (0) e^(-k z)
z = 23.49 m
Adding water vapor to air _______ its density.
B: Decreases
At what depth in the water column is the SOFAR channel?
1 km
What is the approximate declination of the earth? (i.e., the angle of the poles relative to the plane of orbit around the sun):
23.4 degress
At a fixed pressure does sound move faster in colder or warmer water?
faster in warmer water
Wind stress is proportional to wind speed to the power a: Stress ~ (WindSpeed)^a So, the value of a is:
2
At 4000 m depth in the ocean, which one is higher: in-situ water temperature or potential temperature?
As we go deeper into the water column, the local (in-situ) water temperature (t) becomes larger than the potential temperature (Θ)
What three factors determine the density of seawater? Which of these can be measured with the least accuracy?
o Density is a function of:
o Pressure, temperature and salinity
o Pressure is the factor measured with the least accuracy (based on the precision of the measurements)
How is sigma theta different from sigma t?
sigma(t) (σt) = σ(s,t,0) = ρ(s,t,0) - 1000
Where t stands for in-situ temperature.
The effect of pressure is removed.
Does not consider adiabatic temperature changes.

sigma(theta) or sigma(ϴ) or (σ ϴ)
σϴ is σ(s,ϴ,0) = ρ(s,ϴ,0,) - 1000
Where ϴ stands for potential temperature.
The effect of pressure is removed.
Considers adiabatic temperature changes.
Is surface salinity higher in the equator or mid-latitudes (30 deg)?
Higher at 30 deg (N and S). This is the high pressure latitudinal belt, where evaporation > precipitation.
What two parameters are used to measure sea water salinity?
Conductivity or chlorinity (measured directly or via silver)
Subtropical gyres all have _________ rotation.
b. negative relative vorticity
Subpolar gyres all have _________ rotation.
a. positive relative vorticity
Mixed layer depths show the greatest seasonal variability at:
b. temperature latitudes
In the Northern Hemisphere inertial currents rotate in a
b. clockwise direction
At higher latitude, inertial periods
b. decrease
Under the influence of a constant zonal wind, the depth of the Ekman layer will __________ with increasing latitude.
b. decrease
Ekman spirals do not exist
c. at the equator
Which of quantity is used to estimate vertical flow in the ocean?
c. curl (tau/f)
The magnitude of the Coriolis force:
c. is modelled as the sine(latitude)
The rate of change in the Coriolis force with latitude (i.e., df/dy)
b. decreases with increasing latitude
List the 5 assumptions underlying the calculation of the Ekman equation:
1. No Acceleration (i.e., steady consistent wind)
2. Constant Az (eddy viscosity in vertical)
3. No boundary friction (i.e., no horizontal boundaries)
4. No bottom friction (i.e., infinite depth)
5. f (coriolis parameter) varies very little with latitude. Basically, constant Coriolis force acts on the water
Explain westward intensification in the subtropical gyres using your understanding of relative vorticity supplied by the wind and changes in relative vorticity due to meridional transport of rotating parcels of water and friction with coastlines.
Stommel's contribution entails working out vorticity for the subtropical gyres, by balancing the components relating to the wind forcing, the change in latitude of water parcels, and the friction along the coast. Western intensification of the gyres, whereby flow is strongly concentrated along the western coast of the basin leading to large positive vorticity from friction, is needed to balance the other vorticity components. This leads to an asymmetrical gyre that is in equilibrium, and does not speed up or slow down.
Show a generic equation for how we calculate gradients in temperature and salinity in the ocean, making sure you explain each term of the equation and indicating the units:
Gradient = (Value 1 - Value 2) / Distance
Units = degree C / m and PPSU / m
Answer these questions based on the CTD data you analyzed:
were temperature gradients larger in the vertical or in the horizontal
vertical
Answer these questions based on the CTD data you analyzed:
what was the largest temperature gradient you observed
0.12 deg. C/m
Answer these questions based on the CTD data you analyzed:
were salinity gradients larger in the vertical or in the horizontal
vertical
Answer these questions based on the CTD data you analyzed:
what was the largest salinity gradient you observed
0.013 PSU/m
You deployed surface drifter drogued at 2.5 m depth in a shallow bay (< 15 m depth) and the wind during the deployment was 20 m / s from the north-east (compass heading of 45 degrees).
If latitude = 30 deg N, what is the Ekman layer depth (Ed)
Ed = (4.3 * 20) / sqrt (sin(30)) = 86 / sqrt(0.5) = 122 m
You deployed surface drifter drogued at 2.5 m depth in a shallow bay (< 15 m depth) and the wind during the deployment was 20 m / s from the north-east (compass heading of 45 degrees).
What direction do you expect the surface water to flow. For full credit explain your rationale?
Because the depth of the bottom is much shallower than the Ed, the surface layer (going 45 degrees to the right of the wind) may be influenced by friction from the bottom and the shore. Therefore, the direction will be close to (but less than) 45 degrees to the right of the wind,
You deployed surface drifter drogued at 2.5 m depth in a shallow bay (< 15 m depth) and the wind during the deployment was 20 m / s from the north-east (compass heading of 45 degrees).
What direction do you expect the Ekman layer to flow. For full credit explain your rationale?
Because the depth of the bottom is much shallower than the Ed, the Ekman spiral will not be fully developed. Thus, only the surface layer (going 45 degrees to the right of the wind) and maybe the layer below (going at 45 degrees to the right of the surface) will occur. Moreover, these layers will be exposed to friction from the bottom and the shore. Therefore, the direction will be close to (but less than) 90 degrees to the right of the wind, and likely close to the direction of the surface flow (about 45 degrees to the right of the wind).
This is the actual track of the drifter, showing equally spaced time points. Briefly describe its behavior. (see Midterm 1 Key)
Flowing to the SW (heading of about 200 degrees), and speeding up over time.
List two assumptions that could be responsible for the mismatch between the expected drifter track, given Ekman theory, and the observed track.
o Friction with the bottom, the sides of the channel and the shore
o Pressure gradients may be at play, due to influx of freshwater from rivers and oceanic water from offshore
o Water seems to be accelerating (see track in previous question)
o Wind speed (and direction) may not be constant over time
Finally, list two other factors that could be responsible for the observed drifter track.
o The wind may affect the surface floats attached to the drifters
o Other currents, due to pressure gradients and tides, may be at play
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