Physical Oceanography Flashcards
What is the average depth of the ocean?
3.8km
Whats the ~ width of the continental shelf?
~65km
What is the aspect ratio of the ocean (width: depth)?
2500:1
What is the temperature range of the ocean?
-2°C at the poles to 28°C at the equator
What is the primary influence of the ocean temperature?
air-sea interface
inertia
Trägheit
Compare the thermal inertia of the ocean compared to the atmosphere
- energy required to heat the atmoshpere by 1°C would only heat up the first 2m of the ocean
- from the greenhouse effect, ocean has taken 20x as much heat, but warmed up less then the atmosphere.
How deep is the mixed surface layer of the ocean?
ca. 100m
What is the weight percentage of the salt in the ocean?
3.5 %
also called 35 psu (practical salinity units).
Is the salinity equally distributed?
Nope:
- varying geographically: according to evaporation, precipitation, rivers, ice formation and ice melt
- salinity changes with depth: halocline!
* in cold water the halocline helps stabilizing the water column, lower salt above allowing the formation of ice, increasing. where heavy evaporation more salt above, which is heavier, resulting in mixing.*
How much does the pressure increases with depth in the ocean?
1 bar per 10 meters
(or 1 atmosphere per 10 meter)
Pressure is one of the major driver for ….. in the ocean.
circulation
On which three factors does the density in the ocean depens on?
- salinity
- pressure
- temperature
give a range for seawater density
1020 – 1030 kg/m
the average density is 1025 kg/m!
Connection between pressure and density
?
water becomes denser with increasing density
what are the properties of
lighter water vs. heavier water?
lighter water: warmer, fresher
heavier water: colder, more saline
whats a pycnocline?
sharp density cline
name for sharp density cline
pycnocline
Dissolved oxygen is an indicator for what?
when the water was last in contact with the athmosphere
Name conservative and unconservative tracers
- *unconservative**:
- dissolved oxygen
- phosphate, nitrite, silicate (usually found away from surface the socalled euphotic zone)
- *conservative**:
- radioactive elements (tell something about turnover rates)
Ocean currents – wind driven circulation
How does the angle of the sun influence the heating?
lower angle, more is reflected…
The proportion of reflected
energy is called…
albedo
Differential heating is caused by:
- day/night
- seasonal changes
- over the years
Averaged over the whole planet, energy in and out is balanced!
BUT there is a net energy GAIN at low-latitudes (the tropics) and a net energy LOSS at
high-latitudes (the poles).
So why doesn’t the tropics keep getting warmer and the poles keep getting colder?
There has to be a transfer of heat from the equator to the poles
By ocean and by atmoshpere
Atmosphere: name the different cells
- polar cell
- ferrel cell
- hadley cell
overturning circulation
Ocean Measuring Instruments:
- *CTD**
- Conductivity, Temperature, Depth*
Niskin bottles on a metal frame, used to collecvt water samples.
From these samples also phosphate, nitrate, dissolved oxygen, siicate and CFC can be determined.
Niskin Bottle: can be opened at both ends. The open bottle is lowered into the ocean until it reaches a certain depth and then the bottle is closed by a weighted trigger. Niskin bottles are often either set up in a series of individual bottles that trigger each other in turn as they close, or they are set up in a circular rosette of as many as 24 bottles attached around a CTD instrument. Either arrangement allows samples to be taken at different water depths. The water collected by Niskin Bottles is used for studying plankton or measuring many physical characteristics such as salinity, dissolved oxygen, nutrient concentrations (such as phosphate, nitrate and nitrite), and dissolved organic and inorganic carbon.
Ocean Measuring Instruments:
Current Meters
can be in oceans for years.
Record: current speed & direction
+
temperature, conductivity
Ocean Measuring Instruments:
Thermistor strings
measure and record the temperature profile throughout the water column
Ocean Measuring Instruments:
Expendable bathythermograph (XBT)
deployed from ships to measure temperature in the surface layers of the ocean (1km)
Ocean Measuring Instruments:
- *ADCP**
- Acoustic Doppler Current Profiler *
measures a profile of the current acoustically, throughout the water column
Ocean Measuring Instruments:
**Tidal gauges **
measure tidal height
Ocean Measuring Instruments:
Satellites
enables us to remotely sense large areas of data, they can measure quantities such as:
- sea surface temperature (SST)
- sea surface height
- Ocean Color
- (biological productivity)
- surface winds
- sea ice cover
- bottom bathymetry (Meerestiefenmessung)
Which forces drive the ocean?
- gravity (sun, moon)
- pressure force
- friction (predominantely at boundaries)*
- wind (only at surface boundary)
- seismis forces
- coriolis*
* = secondary forcers, only affect water, once it is already in motion
Name the three defining characteristics of GFD
GFD = geophysical fluid dynamic
- aspect ratio
- stratification
- rotation
Coriolis Effect
The Coriolis force :
• acts at right-angles to the actual direction
of water motion.
• causes water to move to the right in the
northern hemisphere
• causes water to move to the left in the
southern hemisphere.
Wind forcing:
What is the extent to which the wind drags the surface water dependent on?
Wind forcing
• Surface winds effectively drag (via friction) the
ocean surface along in the direction of the wind.
• Surface winds are an energy source for the
ocean.
• The extent to which the wind drags the surface
water depends on:
- wind strength
- wave conditions
- density stratification
Formel of pressure
P = height x density x g
What is the geostrophic balance?
• Suppose we have a difference in sea-level height. Water
will be accelerated from the region of high pressure
towards the region of low pressure.
• As the water starts to move, the Coriolis effect (rotation)
deflects the water to the right (NH) or left (SH).
• The water keeps getting deflected until the force due to
the pressure difference balances the Coriolis force.
• This balance is called a geostrophic balance and the
resulting current is referred to as a geostrophic current.
gyre
Due to wind-generated pressure differences and the
Coriolis effect water typically moves in a circular
pattern called a gyre.
direction of the ekman transport on the northern and southern hemisphere
• In the southern hemisphere the Ekman transport is to
the left of the wind.
• In the northern hemisphere the Ekman transport is to
the right of the wind
A definition of surface waves
waves which occur at an interface
(wind generated waves, raindrops, earthquakes, etc.)
** = Generating Force - Restoring Force**
How does the wind speed influence:
- duration in hours of a wave
- average height
- average wavelenght
- average period in seconds
How does the wind speed influence:
- duration in hours of a wave: increase
- average height: increase
- average wavelenght: increase
- average period in seconds: increase
Please, define
Capillary Waves
Waves with a wavelengths less than ~
1.7 cm
in these kinds of wave the principal restoring force is surface
tension
Gravity Waves
Gravity Waves Travel On Density Surfaces
Math. Definition of Wave Speed
Speed = (length of wave) / (wave period) C = L / T
The period of a wave remains the same
(determined by generating force)
Name three different kinds of waves
- shallow waves: depth klein gleich Length / 20
- deep waves: depth grösser gleich Length/2
- transitional waves: alles dazwischen
Definition Wave Train
packets of similar waves with approximately the same
period and speed
Dispersion from a storm: which types of waves come first?
- long waves
- combined long and intermediate period waves
- long, intermediate and short waves combined near the storm
- > waves sort themselves out with distance
