Exam questions Flashcards
What is potential temperature?
Potential temperature is the temperature a water parcel would have if it were moved adiabatically (without exchange of heat) to a reference level, usually the surface. It removes the pressure effect that heats a water parcel when it is compressed by high pressure (weight of water column).
What are hydrogen bonds?
A hydrogen bond is the electrostatic attraction between two polar groups that occurs when a hydrogen (H) atom covalently bound to a highly electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F) experiences the electrostatic field of another highly electronegative atom nearby.
List three unique properties of water that can be attributed to hydrogen bonds.
In the solid state, the particles of matter are usually much closer together than they are in the liquid state. So if you put a solid into its corresponding liquid, it sinks. But this is not true of water. Its solid state is less dense than its liquid state, so it floats.
Water’s boiling point is unusually high. Other compounds similar in weight to water have a much lower boiling point.
Another unique property of water is its ability to dissolve a large variety of chemical substances. It dissolves salts and other ionic compounds, as well as polar covalent compounds such as alcohols and organic acids.
Water is sometimes called the universal solvent because it can dissolve so many things. It can also absorb a large amount of heat, which allows large bodies of water to help moderate the temperature on earth.
Water has many unusual properties because of its polar covalent bonds. Oxygen has a larger electronegativity than hydrogen, so the electron pairs are pulled in closer to the oxygen atom, giving it a partial negative charge. Subsequently, both of the hydrogen atoms take on a partial positive charge. The partial charges on the atoms created by the polar covalent bonds in water are shown in the following figure.
What does salinity do to the freezing point of seawater?
Saltwater has a much lower freezing point (the freezing point is the temperature where something freezes) than freshwater does. And the more salt there is in it, the lower the freezing point gets. So in order to know the exact temperature that it’s going to freeze, you have to know just how salty it is. For saltwater that’s as saturated as it can possibly get (i.e. there’s no way to dissolve any more salt in it no matter how hard you tried), the freezing point is -21.1 degrees Celsius. This is when the saltwater is 23.3% salt (by weight).
How does density of seawater depend on temperature, salinity and pressure?
Density increases with decreasing temperature, increasing salinity and increasing pressure.
What is compressibility?
It is a measure of how much volume a parcel of water/air decreases when pressure increases.
Increasing pressure decreases the volume of a water parcel (about 0.5% each thousand meters).
Which processes can increase temperature, and which can decrease temperature in the ocean?
Increase:
- incoming shortwave radiation from the Sun
- incoming longwave radiation from the atmosphere
- conduction of sensible heat from warmer air toward cooler water
- gain of latent heat through condensation
- movement (advection) of warmer water into a region
Decrease:
6. emitted longwave radiation from the surface to the atmosphere
7. conduction of sensible heat from warmer water toward cooler air
8. loss of latent heat through evaporation
9. movement (advection) of cooler water into a region (not shown).
(+ ice melting)
Which processes can increase salinity, and which can decrease salinity in the ocean?
Increase: latent heat flux (evaporation), water freezing
Decrease: precipitation, ice melting
Give two possible explanations for why the Pacific Ocean is less saline than the Atlantic Ocean.
Evaporated water from Atlantic Ocean is transported in clouds by Trade winds and is added to Pacific Ocean as precipitation.
Which process can change temperature and salinity in the interior of the ocean?
Instability of the water masses. Mixing of the water masses
Explain a seasonal thermocline, as displayed in the figure from Ocean Weather Station Papa in the North Pacific Ocean
A thermocline which develops in the oceans in summer at relatively shallow depths due to surface heating and downward transport of heat caused by mixing of water generated by summer winds.
Spring —> creation of thermocline
Summer —> Bigger thermocline
Autumn —> Smaller thermocline than summer
Winter —> No thermocline or very liitle depending on latitudes
Define the following terms, and their relationship: thermocline, halocline, pycnocline and stratification.
A cline is a sharp increase or decrease in the vertical of a property; thermocline for temperature, halocline for salinity and pycnocline for density. Stratification refer to the vertical distribution of density. And is usually connected to stability of water column. A water column is stratified if density increases more with depth than the pure pressure effect on the density would cause.
The figure shows typical TS-profiles of upper water masses in the four subtropical gyres. Draw the profiles as T and S and density against depth. What do we call such a shape in the stratification? Discuss what decides that the four profiles displayed in the figure become different from each other.
Differences in surface heating and evaporation/precipitation. Southern gyres are heated more than northern gyres. Atlantic gyres evaporate more than Pacific gyres.
Why is the Pacific Ocean less saline than the Atlantic Ocean?
Evaporated water from Atlantic Ocean is transported in clouds by Trade winds and is added to Pacific Ocean as precipitation.
What do we mean by the concept ‘surface mixed layer’?
Surface mixed layer is the surface layer with homogeneous properties due to wind mixing.
Surface heat flux which has four terms; shortwave radiation, longwave radiation, latent heat flux and sensible heat flux. Describe in short the four terms and what influence them.
Shortwave radiation is radiation from the sun and increases with solar altitude angle (distance from horizon) and decreases with cloud cover.
Longwave radiation is net radiation from the surface (surface radiation minus back radiation from clouds and atmosphere). Decreases with cloud cover.
Latent heat flux is mainly evaporation, which generally cools the ocean. It increases with increasing wind (turbulence) and try air, and also if the air is unstable (colder than the ocean). Sensible heat flus is conduction of heat between ocean surface and atmosphere. It increases with increasing temperature difference and wind speed (turbulent flux).
Explain in short the Coriolis effect.
The Coriolis effect is an effect of an object moving in a straight direction relative to space, but the earth surface rotates below the moving object. (a straight line in a rotating axis system). Locally the effect looks like an object moving over a merry-go-round. The Coriolis effect can be formulated as a force acting 90° to the right/left of the velocity direction in NH/SH.
Describe how you would deduce direction and strength of Ekman transport.
Ekman transport is the total transport in the Ekman layer, and is balanced by the wind stress and the Coriolis force equal to the formula wind stress/Coriolis parameter. Ekman transport has direction 90° to the right/left of the wind direction in NH/SH.
What is an Ekman layer and what determines the Ekman depth?
The Ekman layer is the depth where the Ekman spiral reaches. At each water level in the Ekman layer the Ekman velocity is balance by three forces: The shear stress from above, the friction from the layer below acting in opposite direction of the Ekman velocity, and the Coriolis force acting 90° to the right/left of the Ekman velocity direction in NH/SH. The Ekman depth is determined by the strength of the eddy viscosity; shallow if the eddy viscosity is weak and deeper if the eddy viscosity is strong.
What is Ekman pumping?
Ekman pumping is downwelling in a region where the Ekman transport converge. It happens because volume is conserved in a box bounded by the Ekman depth and a horizontal square. If the Ekman transport converge it transport more water into the box than out of the box, so water has to exit the box vertically.
The figure (b) describes the upwelling process along the equator. Describe this process in words.
Right at the equator there is no Coriolis effect, and thus no Ekman transport, and the Trade winds blowing towards the west will drag a surface current in the same direction. However, only a 1/4° away from equator the Coriolis effect starts working and the Trade winds will cause an Ekman transport away from the equator 90° to the right/left of the wind direction in NH/SH. Ekman transport remove water from the equatorial region and is replaced by water from the deep; upwelling.
Describe the upwelling process in a typical Eastern Upwelling Region.
An Eastern Upwelling region is located on the eastern side of an ocean basin. Equatorward winds will there lead to Ekman transport away from the coast. Water is then removed from the area closest to the coast and that water is replaced by water from below; upwelling.
What are the characteristics of western boundary currents? Name the western boundary currents in the subtropical gyres of the North Pacific and North Atlantic ocean.
A western boundary current is characterized by flowing on the western side of a basin, and it is narrow and swift (strong current) such that friction against the coast is an influence. It can move both northwards and southwards. The western boundary current in North Pacific subtropical gyre is called the Curoshio Current and in the North Atlantic subtropical gyre the Gulf Stream.
