Download Ch 9 Homework Answers

PSc 201
Chapter 9 Homework Answers
Critical Thinking Questions
1.
counterclockwise
2.
current d
3
At the surface in the northern hemisphere the flow is to the right of the direction of the wind across
the water. This flow of water at the surface exerts a friction force on the next lower layer of water,
which then actually flows at an angle to the right of the surface flow, and so on for deeper layers, all
flowing somewhat to the right of the layer above.
4.
North Equatorial (warm), Kuroshio (warm), North Pacific (warm), California (cold)
5.
North Equatorial (warm), Gulf Stream (warm), North Atlantic (warm), Canary (cold)
6.
a) eastern boundary currents
b) the east to west transverse currents
c) western boundary currents
7.
a) because the coriolis effect is much stronger at higher latitudes farther from the equator than it is
near the equator
b) Since the east to west transverse currents just north of the meteorological equator flow until they
hit a continent, and then turn north with help from the weak coriolis effect, the flow north along the
continent is jammed against the continent and is narrow and deep as a result. The west to east
transverse current at higher latitude experiences a much stronger coriolis effect and much of this flow
turns south before it encounters a continent, causing the south flowing eastern boundary current to be
broad and shallow.
8.
The typical summer winds near the US west coast blow from the northwest and pass over the cold
California Current before reaching land, which cools the air. The typical summer winds near the US
east coast blow from the southeast and pass over the warm Gulf Stream current before reaching land,
which warms the air.
9.
The difference in climate is because the air over London in the winter has passed over relatively warm
ocean water delivered by the Gulf Stream but the air over Ontario, Canada in the winter has passed
over thousands of miles of very cold land and over very cold ocean before reaching land.
10. Because the typical wind blows from the northwest almost parallel to the coast, and this sets coastal
surface water into motion, but not parallel to the wind. The surface water makes its northern
hemisphere right turn and moves away from the shore, allowing deeper colder more nutrient rich
water to come to the surface. That is why our coast is so rich in sea life. A similar situation exists
along the west coast of Chile and Peru in South America where the winds tend to blow from the
southeast along the coast and surface water again moves away from the shore allowing strong
upwelling.
11. Since the meteorological equator is usually 5 to 8º north of the geographic equator, the South
Equatorial Current often flows along the geographic equator. The coriolis effect is zero exactly at the
geographic equator, but begins to be felt by the current even a short distance from the geographic
equator. Since the coriolis effect causes right turns in the northern hemisphere and left turns in the
southern hemisphere, the water in the current tends to flow somewhat away from the geographic
equator on both sides. This allows colder deeper nutrient rich water to come to the surface right
along the geographic equator. See Fig 9.15 a for its useful diagram.
12. failure of the trade winds causes an El Nino event
13. The westward flowing transverse currents (the North Equatorial Current and the South Equatorial
Current) driven by the trade winds pile up water at the west side of the Pacific, which causes sea level
to usually be about 1 m higher on the west side than on the east side. When the trade winds weaken
or fail completely, which happens on average about every four years, warm surface water which has
piled up on the west end of the equator can flow back across the Pacific all the way to the coast of
South America and Central America. This warm water shuts down the usual upwelling along the
coast and causes downwelling instead, so there are fewer nutrients in the water and the fish and
marine mammals tend to go elsewhere to find food. Fishing fleets find few fish. A typical El Nino
event lasts about one year, but a severe El Nino can last several years and the effects can reach as far
north as California. We also tend to have more rain than usual along the coast in California during
an El Nino winter. Eventually the trade winds start up again and the situation can become normal
quickly.
14. geostrophic (geo means earth and strophic means turning)
15. cold water is denser, and surface water near the poles becomes cold
Saltier water is denser, and as sea ice forms at least 2/3 of the salt is expelled from the ice as it forms
leaving the remaining surface water much saltier (more saline) than average, and thus denser. This
cold salty water may sink to the bottom and then travel toward the equator as part of the deep
circulation (thermohaline circulation).
16. When cargo containers containing Nike shoes and rubber ducks fell off of cargo ships during severe
storms the shoes and ducks were released at a known location and a known time. Be finding out
where a lot of these shoes and ducks ended up on beaches, some information about surface currents
was learned.
17. There are now over 3,000 Argo Floats in operaton and these floats have accurately measured the
surface ocean currents.
18. Global warming causes polar ice to melt and flow into the ocean and also causes more precipitation at
high latitudes, both of which cause the surface water to become less saline (fresher). This may
already have decreased the flow of the northern Gulf Stream and may also make it difficult for polar
water to become dense enough to sink and become part of the deep water currents. If currents like
the North Atlantic Current (a northern branch of the Gulf Stream) become weakened or disrupted,
very unpleasant climate changes will occur for England, Europe, and the Scandanavian countries.
Analytical Thinking Questions (none for this chapter)