UNIVERSITY OF OSLO
Faculty of Mathematics and Natural Sciences
Exam in
Day of exam:
Exam hours:
GEF 2610 ­ Physical Oceanography Monday 4th June 2012
14:30 ­ 17:30
This examination paper consists of 3 pages.
Appendices: 1 map (2 copies)
Permitted materials: Calculator Make sure that your copy of this examination paper
is complete before answering.
Question 1. (20 p)
a) Set up the Equation of Motion (Newton's Second Law) with the terms that are used in physical oceanography. Define the forces.
b) Explain which forces that are balancing each other when we have a geostrophic current and an Ekman spiral, respectively.
c) Usually there is a net volume transport of water out of the Baltic Sea, while the direction in
the Straits of Gibraltar is into the Mediterranean. Explain the opposite directions in the two cases. Which forces are driving the transports? d) Which wind systems are driving the major gyres of surface currents in the world oceans? Question 2. Pacific Ocean (40 p)
a) A map of the Pacific Ocean is enclosed. Draw the arrows for the surface currents and name
the currents.
b) In the equatorial region there is a very strong sub-surface current. Name and describe
briefly this current.
c) - Where do we find the greatest depth of the Pacific Ocean? How great is this depth?
- What is the mean depth of the World Ocean (all oceans)?
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d) Which geological process is assumed to be the origin of the deep ocean trenches and the
mid-ocean ridges?
e) During the El Niño and La Niña events the hydrographic conditions in the sea outside
Peru-Ecuador will deviate from the average state. Describe these deviations.
f) El Niño and La Niña can lead to disastrous weather conditions in other regions of the
world. What kind of conditions?
g) Why is the coastal area outside Peru and Ecuador usually an upwelling area?
Question 3. Analysis of Field Data (20 p)
a) At the station Geitholmen the following quanta (PAR) and energy irradiances were
recorded on April 20, 2012:
Depth (m)
0
1
2
5
10
15
20
PAR (μmol m-2 s-1)
424
362
242
89.1
23.1
7.0
2.8
Energy irradiance (W m-2)
212
79.6
53.2
19.6
5.08
1.5
0.62
Make a crude estimate without calculations of the depth of the euphotic zone. What is meant
by this zone?
b) We shall assume that the irradiance at two depths z1 and z2 can be related to each other by
E ( z2 )  E ( z1 ) e  K ( z2  z1 )
where K is the average vertical attenuation coefficient of irradiance between z1 and z2. Based
on the energy irradiance in (a), what are the values of K between 0 and 5 m and between 5
and 20 m?
c) The hydrostatic pressure p at the depth z is defined on integral form as
z
p ( z )  g  ( z ' ) dz '
0
where g is 9.82 m s-2 and ρ is the density. Find the hydrostatic pressure difference at 2 m
depth between the stations Malmøykalven and Oksvaldflua, provided the surface is
horizontal, by using the table below (for simplicity units have been omitted). The density is
expressed as ρ-1000 in units of kg m-3.
Malmøykalven
Oksvaldflua
2
Depth
0
1
2
ρ-1000
25.67
25.77
26.34
ρ-1000
25.36
25.46
25.76
d) How much higher than the surface at Malmøykalven must the surface at Oksvaldflua be in
order to compensate for the calculated pressure difference at 2 m depth?
Question 4. Calculations (20 p)
a) What is the general relationship between the phase velocity c, the period T and the wavelength L of a wave? b) A fresh gale has been blowing for a long time and has resulted in a swell leaving the area with wave height H of 5 m and a period of 13 s. What is the wavelength L of this swell if it follows the relationship for deep water waves c  gL /(2 ) , where g is gravity? What is the
ratio H/L? c) Assume that the described swell enters shallow waters and that the period remains the same, while the phase velocity now follows c  gh , where h is the depth of 5 m to the bottom. What is c and L? d) What do we mean by the significant wave height Hs? Which three major factors related to the wind determine the magnitude of Hs?
END
ENCLOSURE Question 2 - GEF2610-2012
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