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 CIV300 Terrestrial Energy Systems, 2013F Test 2 Question Sheet 1 Test 2 Aid Sheet Exam: A single 8.5 by 11 inch aid sheet (both sides) and Type 2 non-­‐
programmable calculators are permitted. The time allowed for this Test (Part A plus Part B combined) is 90 minutes. Answers are to be written on the answer sheets given (one sheet for Part A and another for Part B). PART A 1. Geostrophic wind describes a wind that:
(a) Flows from an area of high pressure to an area of low pressure (b) Flows from a cold air
mass to a warmer air mass (c) Flows parallel to isobars (d) Flows in a clockwise circular path
with low pressure at the centre in the northern hemisphere
ANS C 2. The primary driver of the Hadley cell is:
(a) Solar energy heating the atmosphere at latitudes close to the equator (b) The Coriolis
force (c) The rotating Earth (d) The large amount of land vs. sea at latitudes close to the
equator
ANS A o
3. A saturated air mass at 30 C is forced to rise vertically by 1 km and then falls vertically by 1
km. A good estimate of its resulting relative humidity would be:
(a) Less than 20%
(b) 20-30%
(c) 30-40%
(d) 40-50%
No correct answer provided – was 50-­‐60%. All awarded 1 mark. o
4. What is the density of air at a temperature of 35 C and a pressure of 101 kPa? Rsp for air =
287
(a) 1.14 gm
-3
(b) 10.05 kgm
-3
(c) 0.1 kgm
-3
(d) 1.14 kgm
ANS D -1
-3
5. A mass of air is moving due east on the equator at 20 kmh . It rises up into the air as a result
of the Hadley cell system before descending to the Earth’s surface at 30° north of the
equator. The Earth has a radius of 6,370km and can be assumed to be a sphere. What
speed will this air move at relative to the ground at its new location? Assume a 24-hour day.
-1
-1
(a) 20 kmh (b) 223 kmh (c) 243 kmh
ANS C -1
(d) 0 kmh
-1
CIV300 Terrestrial Energy Systems, 2013F Test 2 Question Sheet 2 6. Earth is slightly wider at the equator than at the poles. One reason is because of:
(a) The centrifugal force (b) The Coriolis force
force (d) None of the above
(c) The centrifugal force and the Coriolis
ANS A o
7. What is the dew point of an air mass at a temperature of 25 C and a relative humidity of 30%.
o
o
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(a) 6 C (b) 14.5 C (c) 25 C (d) -10 C
ANS A
8. A descending air mass under adiabatic conditions will:
(a) Increase its temperature and relative humidity (b) Become unstable (c) Increase
temperature and decrease in total energy (d) Increase temperature with no change in
energy
ANS D 9. Air that has reached its saturation vapour pressure can:
(a) Result in dew forming (b) Result in rain (c) Not absorb any more moisture (d) All of these
three
ANS D o
o
10. During a thunderstorm, air at 90% relative humidity (RH) and 30 C cools to 15 C and 100%
RH. How much energy is released per kg of air?
(a) 42 kJ (b) 51 kJ
(c) 35 kJ (d) None
ANS B
11. Which of the following contributes to the clockwise flow of the north Atlantic gyre?
(a) Low water salinity (b) The trade winds (c) Temperature differences between deep and
shallow water in the north Atlantic (d) location close to the horse latitudes
ANS B 12. Which two forces are required to be in balance in order for geostrophic winds to occur?
(a) Gravity and pressure gradient (b) Pressure gradient and friction (c) Coriolis and friction
force (d) Coriolis and pressure gradient
ANS D 13. A downdraft wind is a phenomenon related to a thunderstorm. The downdraft is caused by:
CIV300 Terrestrial Energy Systems, 2013F Test 2 Question Sheet 3 (a) High pressure air forming high up in the cloud resulting in a pressure gradient (b) Heavy
rain entraining a flow of air (c) Air compressing and warming as it falls (d) Centrifugal
forces
ANS B 14. What is the air pressure caused by a column of air 20km in height with an average density =
-3
0
0.6 kgm and an average temperature of 0 C?
(a) 117.6 kPa (b) 101 kPa (c) 47kPa (d) 101 Pa
ANS A PART B 1. a) Explain how an approaching cold front can result in the formation of cumulonimbus clouds
when a mass of warm, high humidity air is present. You may also use a diagram. (2 marks)
ANS 1. Cold air is denser so will move to displace (go under) the warmer air forcing it
upwards. That air then hits the dew point resulting in in cloud formation.
b) Describe the conditions in the atmosphere that will result in the ‘runaway’ vertical growth of the
resulting cloud (1 mark)
ANS. Atmosphere must be unstable (environmental lapse rate > saturated lapse rate).
2. (a) What is an atmospheric temperature inversion? Give one example of how it forms. (2
marks).
ANS An atmospheric temperature inversion is a situation where the air temperature
steadily increases from ground level as you increase in height, the opposite of what
typically occurs.
An example of its formation would be cold winds (katabatic) spilling off a cold mountain
top and becoming trapped in the bottom of a valley, displacing warmer air that then rises
above it. Another example would be when warm air moves over an area of existing cold
air and then stays there, or vice versa. Others possible.
(b) Explain how such an inversion results in the formation of a blanket layer of pollution above a
city like Los Angeles or Tehran. (2 marks)
ANS Local warming at ground level can result in a parcel of air detaching itself from the
ground. It rises as its resulting density is lower than that of the surrounding air. As it rises
it cools adiabatically. At a certain point its temperature (and density) will meet that of the
surrounding air, as it is warmer the higher you go within an inversion, and so the
temperatures and densities and pressures eventually match. At that point it has no
remaining buoyancy. The now risen air is then trapped and other air rising will join it,
levelling out at the same altitude and resulting in the blanket layer.
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An unsaturated warm air mass of temperature = 40 C detaches from the Earth’s surface and
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begins to rise. If the environmental lapse rate is 8 C per 1,000m, and the environmental air
CIV300 Terrestrial Energy Systems, 2013F Test 2 Question Sheet 4 o
temperature at ground level is 30 C, at what altitude will the air mass cease to rise? Assume the
air mass remains unsaturated as it rises.(2 marks)
ANS 5,000m. – detached mass loses approx.. 10C with every 1,000m in altitude (adiabatic
lapse rate). The environmental lapse rate is 8C so the temperatures meet at 5,000m in
altitude.
b) If the relative humidity of the detached air mass at ground level is 40%, will we see clouds
forming? Explain your answer. (1 mark)
ANS Relative humidity increases as air moves towards the dew point line on the
psychometric chart. It hits it at 18C / at an altitude of 2,200m. At RH of 100% the moisture
condenses out and we see cloud.
4. A hurricane and a tornado are both examples of massively powerful weather systems that rely
on turning forces.
a) Explain why of the two, only a tornado is able to exist on the equator (1 mark)
ANS a hurricane needs the Coriolis force to form, which is zero at the equator.
b) Name two essential requirements for the growth of a hurricane (2 marks)
ANS Two from…… 1. The continued presence of a warm source of moisture i.e. the sea 2.
Flow imbalance such that the central pressure drops, resulting in continued transportation
of warm moist air into the storm system 3. No disturbing high level wind systems to break
up its formation 4. Stays away from the equator >5 deg. Any other reasonable answer
given due consideration.