Download Midterm 2 solutions

ATMS 211 SQ2008
Midterm 2
12 May 2008
90 pts total
Name SOLNS
Quiz section: A (10:30) / B(11:30)
SECTION 1: Multiple Choice (14 questions; 28 pts – 2 pts each)
Multiple Choice: Circle the letter(s) of the correct answer(s). Three questions have more than one correct
answer. Circle them all.
1. Surface currents in the ocean are primarily driven by
a) surface winds
b) upwelling along the coasts
c) the southward migration of the ITCZ
d) formation of sea ice causes formation of dense,
salty water masses.
2. The Coriolis effect pushes a moving object toward the ___ in the Northern hemisphere and the ____ in the
Southern Hemispheres.
a) Left;left
b) Right; right
c) Right; left
d)Left; right
3. At the northern hemisphere summer solstice (June 21), what section of the globe receives the largest solar
radiation energy flux?
a) the equator
b) the Tropic of Cancer (23.5oN) c) the Tropic of Capricorn (23.5oS)
d) the north pole
4. An air parcel moves upward because
a) its density is greater than the air density surrounding it
b) its density is less than the air density surrounding it
c) its density is the same as the air density surrounding it
d) its pressure is less than the air pressure surrounding it
5. Each of the following causes uplift in the atmosphere except:
a) buoyant air rising
c) release of latent heat
b) subsidence
d) air motion moving over a mountain range
6. The ITCZ migrates northward and southward because
a) the latitude of direct solar radiation shifts seasonally.
b) Subsidence in the subtropics shifts northward and southward
c) the easterly trade winds change direction.
d) the ITCZ doesn’t shift northward and southward.
7. The Coriolis force is caused by _______;
a) upper level westerly winds in the mid latitudes
b) circulation of ocean gyres
c) rotation of the earth
d) tilt of the earth with respect to the plane of the ecliptic.
8. Ice particles fall from the upper troposphere and melt turning to rain as they fall. There are 3 g of ice particles in
each kg of air. How much energy is absorbed by the ice particles in each kg of air as they melt? The latent heat of
vaporization is about 2500 J/g, and the latent heat of fusion is about 330 J/g.
a) 990 J
b) 7500 J
c) 8490 J
d) 990,000 J
9. What happens to the temperature of the surrounding air as a result of the absorption of latent heat in the
previous question? The specific heat of air is roughly 1 J/g/K.
a) it increases.
b) It decreases.
c) It stays the same.
10. Atmospheric carbon, as CO2 in the preindustrial atmosphere, was slightly more than 600 Gt. If the amount
leaving the atmosphere going into the oceans was 60 Gt/yr, and the amount leaving the atmosphere going into the
terrestrial biosphere is 60 Gt/yr, what is the residence time of carbon in the atmosphere? A Gt (gigaton) is 109 tons.
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a) 5 yrs
b) 10 yrs
c) 20 yrs
d) 600 yrs
11. The atmosphere is a reservoir of carbon dioxide. If the amount of CO2 in the atmosphere is ____, it means
that rate of addition of CO2 is _____ the rate of depletion of CO2.
a) Increasing; faster than
d) decreasing; faster than
b) Increasing; slower than
e) decreasing; slower than
c) constant: the same as
12. A multi-year mean SLP (sea level pressure) in July measured at Darwin is 1012.8mb. The July 2007 SLP at
Darwin is 1014.2 mb. What is the July 2007 SLP anomaly for Darwin?
a) 1.4 mb
b) 1012.8 mb
c) 1014.8 mb
d) 9.9 %
13. Ocean gyres
a) transport heat poleward
b) circulate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere
c) have upwelling in the center
d) are caused primarily by surface winds
14. Land surfaces heat up and cool down much more quickly than ocean surfaces because:
a) Land surfaces have a lower heat capacity
b) Absorption of solar radiation over land surfaces occurs in a much thinner layer
c) The ocean surface can mix heat downward in turbulent layers, providing more heat storage.
d) Land has higher surface albedo than the ocean
SECTION 2: True / False (5 questions; 10 pts – 2 pts each) Circle the correct answer.
True False
15. Horizontal convergence of air at the surface results in some air moving downward.
True False
16. The polar front zone shows a strong meridional temperature gradient.
True False
17. Buoyant forces affect both atmospheric and oceanic vertical motions.
True False
18. Salty water is less dense than fresh water.
True False
19. The specific heat of water is much lower than the specific heat of air.
SECTION 3: Short Answers – answer in one or two sentences. Choose 4 out of 5. (12 pts - 3 pts each).
1. Does convection in the atmosphere lead to convergence or divergence of surface winds? Why?
Convection leads to convergence of surface winds as air moves into low pressure area created by rising air.
2. Do surface winds from the Arctic rise above or sink under the northern hemisphere midlatitude southerly
winds. Why?
Surface winds from the Arctic sink under NH midlatitude southerly winds because the air is colder and denser.
2. Draw a side view diagram and/or describe the sea surface height anomaly through the center of an ocean
gyre. Does this lead to downwelling or upwelling? Describe why in terms of convergence/divergence and
Ekman transport.
Sea surface height is raised in the center of the gyre due to the
convergence of water caused by Ekman transport. (Ekman
transport is 90 deg to the right of the currents.) This convergence
leads to downwelling of water mass in the center of the gyre.
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3. Label the three latitude belts in each
hemisphere on the following diagram.
See diagram.
4. Explain why westerlies prevail in the upper troposphere in both hemispheres.
Westerlies prevail in the upper troposphere because upper level meridional flow is generally poleward in both
hemispheres. The Coriolis force acts in such a way to turn the flow toward the east, resulting in westerly flow in
each hemisphere. (Arguments for geostrophic flow in the midlatitudes resulting in westerly upper tropospheric
flow are also acceptable.)
SECTION 4: Problems Do 4 of 5 questions (if you finish all 5 questions, the one with the lowest points will
not be considered). Show your work in the space provided. Use additional paper if necessary. Draw a
box around your answer for each section. Show your work. 10 Pts each.
1. Feedbacks
Complete the following two feedback loops. Use an arrow
to indicate positive coupling, and an open
circle to indicate negative coupling. Indicate whether each is a positive or negative feedback,
and
whether each is stable or unstable.
Surface
Temperature
Outgoing IR
radiation
Surface
Temperature
Atmospheric
H2O
Feedback: ___Negative______
Feedback: ____Positive_____
Stability: ____Stable _____
Stability: ___Unstable_____
2. Heat transport
Given the following diagram of absorbed solar radiation and outgoing infrared radiation averaged across latitudes.
a) Label the areas of energy surplus and energy deficit
in the diagram. Draw arrows for the direction of energy
transport. (4pts)
b) In terms of energy balance, describe how we know
energy must be transported. (3pts)
Energy in must balance energy out. In the tropics more
solar is incoming than outgoing longwave, and more
longwave is outgoing in the extratropics than incoming
solar, therefore we know there must be a net transport
of energy toward the poles from the tropics.
c) What systems are responsible for this transport?
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(3pts) atmosphere and ocean
3. Gyre Transport
Given the following diagram of ocean surface currents. Type I roughly shows present configurations. Type II
shows a modeled result. You can use the letters to refer to the current branches in your short answers below.
Answers are acceptable as long as
they make plausible references to
heat transport by currents. The
following are examples.
a) In which case would we expect the GIN seas
(Greenland, Iceland, and Norwegian Seas) to be
warmer? Why? (4 pts)
Case I currents C and B flow from southern
latitudes, carrying more heat to the GIN seas than
I, J K in case II.
b) In which case would Arctic sea ice extend
further south? Why? (3 pts)
Case II currents H and I are relatively cooler in the subarctic region than the currents in B, and so more sea ice
could form further south along the coast of Greenland.
c) Would temperatures in western Europe be warmer in case I or case II? Why? (3 pts)
Case I would bring warmer currents (C and B) closer to Europe, and influence land temperatures accordingly.
4. SVP question and latent heat
Using the following diagram of saturation vapor pressure. (2 pts
each)
a) What is the relative humidity of a parcel of air that has a
water vapor pressure of 15 mb, and a saturation vapor
pressure of 30mb.
RH = VP/SVP = 15/30 x 100 = 50%.
b) What is the temperature of this parcel of air?
Temperature is 24 deg C
c) Assume the parcel is lifted by convection to a height where
the temperature is 18º C. Will the air condense at this level?
Why or why not?
Parcel moves to “C” on the diagram – straight to left following
decrease in T. The air will not condense because the vapor pressure
of the air (15 mb) is still lower than the SVP for that temperature
which is 18-20 mb.
d) Assume this parcel of air is raised further, lowering the temperature to 5º C. Will a cloud form in this
parcel? What will be the relative humidity?
The parcel moves still further left toward lower temperature, at 15 mb, then follows blue line down to 'D'. The air
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can not hold 15mb of water vapor pressure at 5 deg C, so some must have condensed. A cloud will have formed,
and the relative humidity will be 100%.
e) Is heat released or absorbed in this process, and how does it affect the convection of this parcel of air?
Heat is released in the process of condensation, which is added to the air contained in the parcel, adding to the
ability of the parcel to rise through convection.
5. Monsoons
a) Label either a high or low pressure over the Tibetan plateau, northeast of India, on each maps below
corresponding to summer and winter seasons. What causes the high/low pressure in each case?
Summer radiative heating over the Tibetan Plateau causes convection and a low pressure region. Winter radiation
on the Plateau is reflected by snow (high albedo) and very cold, contributing to a high pressure region. It is also
the area of subsidence of the ITCZ.
b) Draw arrows indicating the general direction of the surface winds for each season in relation to the high/low
pressure. How do the high/low pressures drive surface winds?
Summer low pressure draws warm, moist air across the Indian subcontinent from the Indian ocean. Winter high
pressure drives dry, cold winds down from the Plateau.
c) How do the winds affect precipitation over India in each case?
Summer winds are uplifted over India and the Himalayas, causing intense rainfall in the region. Winter winds are
dry, and so little precipitation is associated with them.
NH Summer (JJA)
NH Winter (DJF)
SECTION 5: Extra Credit (4 pts)
1. We've learned that pressure gradients in the atmosphere drive winds from areas of high pressure to areas of
low pressure (as in a). Using the pressure gradient force, and Coriolis force, describe how geostrophic winds (as
in b) arise perpendicular to the pressure gradient. Geostropic balance describes the dominant winds in the
atmosphere. What is the resulting circulation around a low in each hemisphere, assuming the high is equatorward
of the low.
The pressure gradient force causes winds as in (a), but in the NH these are turned to the right by the Coriolis force.
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The resulting geostrophic wind is a balance between the PGF and Coriolis forces. If the wind turned further south
in (b), the PGF would restore it northward, and if the PGF pushed it northward, the Coriolis force would turn it
southward again.
Circulations around a Low are counterclockwise in the NH and clockwise in the Southern hemisphere. You can
think of (b) as a Low with a series of high pressure areas around it, each resulting in the flow such that the low is
on the left.
(a) for NH
L
(b) resulting geostrophic winds
L
H
H
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