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ATS 351, Spring 2009
Week 12, Lab #9 – due April 15/16th
Ocean & Atmosphere General Circulation;
Fronts & Cyclones – 58 points
Question #1: Single-Cell Model & General Circulation (8 points)
To compensate for the surplus and deficit of radiation in different regions of the
globe, the atmospheric winds and ocean currents redistribute the energy equally around
the earth. If we make the following assumptions about Earth: (1) The earth’s surface is
uniformly covered in water, (2) The sun is always directly over the equator, and (3) the
earth does not rotate, we can construct a simple model (Single Cell Model) of the
atmosphere’s general circulation. For the following questions, the answer is either at
the poles or at the equator.
(a) Where is the warmest air found? At the equator
(b) Where is the highest surface pressure found? At the poles
(c) Where would you expect rising air? At the equator
(d) Where would you expect sinking air?
At the poles
Question #2: Three-Cell Model & General Circulation (14 points)
Below is the three-cell model of the Earth’s general circulation.
Polar Cell
Ferrel Cell
Hadley Cell
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a) (6 points) Identify each of the meteorological features by correctly associating
the letter with the features listed below.
Equatorial low: B
Northeast trade winds: F
Westerlies: D
Polar front: E
Southeast trade winds: A
Polar easterlies: C
b) (3 points) Referring to the figure above, how many cells (in the Northern
Hemisphere) do you see? Please label (by correct name) the cells on the diagram
above.
3 cells – Hadley, Ferrel, and Polar cells
c) (5 points) Using the global precipitation distribution map below, explain why
there is a large amount of annual precipitation over the equator but low amounts
in the subtropics.
This is due to the combination of the Hadley and Ferrel cell circulations. Air
generally rises at the equator, leading to significant condensation and
precipitation. Air actually sinks in the sub-tropics, thus hindering convection and
precipitation.
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Question #3: El Nino/La Nina (12 points)
a) Describe the conditions in the Pacific Ocean during an El Nino event. How do
these differ during a La Nino event?
In the Pacific Ocean during an El Nino event, the trade winds reverse and
create warmer than average temperatures in the eastern Pacific. Warmer
temperatures create more convection in the eastern Pacific. During normal
conditions, the western Pacific receives a lot of convection and precipitation but
during an El Nino, it is rather dry.
In the Pacific Ocean during a La Nina event, the trade winds are stronger
than normal and unusually cold surface water reaches the Central and Eastern
Pacific – extreme cold event.
b) What type of weather (cold/warm, wet/dry) would you expect over North
America during a strong El Nino? During a strong La Nina?
El Nino: wet/cool in California and throughout the South; warm and drier weather
throughout a lot of North America
La Nina: wet/cool winter for Pacific NW; in winter, southern months tend to be
warmer and drier than normal
Question #4: Air Masses (8 points)
What type of air mass (cP/cA, mP, mT, or cT) would be responsible for the
weather conditions listed as follows?
a) Hot and dry weather - cT
b) Heavy snow showers and low temperatures at Buffalo, NY - mP
c) Hot, muggy summer weather in the Midwest and the East - mT
d) Record low winter temperatures in South Dakota - cP
e) Daily afternoon thunderstorms along the Gulf Coast - mT
f) Heavy snow showers along the western slope of the Rockies - mP
g) Refreshing, dry breezes after a long summer hot spell on the Central Plains - cP
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h) Warm and moist weather - mT
i) Persistent cold, damp weather with drizzle along the East Coast - mP
Question #5: Mid-latitude Cyclones (10 points)
Describe the process of how a mid-latitude cyclone develops, becomes mature,
and then becomes occluded (drawing pictures will help explain). Which stage the storm
system is most intense? What makes the storm system die? How long do these systems
usually last?
(This is very detailed, do no expect as much from the students – pictures with some
explanation is good)
It begins as a stationary front that is part of the polar front. This sets up cyclonic
wind shear and a wavelike kink forms on the front (2nd figure). This figure shows a
newly formed wave with a cold front pushing southward and a warm front moving
northward. Steered by the winds aloft, the system typically moves east or northeastward
and gradually becomes a fully developed open wave in 12 to 24 hours (3rd figure). As the
open wave moves eastward, its central pressure continues to decrease and winds blow
more vigorously (4th figure). The faster-moving cold front eventually overtakes the
slower moving warm front and the system becomes occluded (5th figure). When an
occlusion forms, the storm is usually most intense (with clouds and precipitation covering
a large area). The center of the intense storm system gradually dissipates, because cold
air now lies on both sides of the occluded front. Without the supply of energy provided
by the rising warm, moist air, the old storm system dies out and gradually disappears (6th
figure). The entire life cycle of a wave cyclone can last from a few days to over a week.
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Question #6: Fronts (6 points)
Use the SLP map shown below to answer the following questions about the
pictured mid-latitude cyclone.
a) Using the isobar analysis (red lines, mb), does the center of the above cyclone
have a relatively high or low-pressure center compared to the surrounding
environment?
Relatively low pressure
b) A cold front is the boundary between the cold, dry cP air and warm, moist mT air.
There is also usually a clear wind shift (change in wind direction) and a
significant (~ 10°F) temperature change at this boundary. If there is a cold front
associated with the mid-latitude cyclone, label this cold front on the above map
using the appropriate symbol.
Above – cold front line is blue with triangles pointed towards warmer air
c) A warm front is the boundary between the warm, moist mT air and the cooler,
moist mP air. There is usually a slight wind shift at this boundary as well. If there
is a warm front associated with the mid-latitude cyclone, label this warm front on
the above map using the appropriate symbol.
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Above – warm front line is red with half circles pointed away from warmer air.
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