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Surface Processes and the Hydrosphere Unit
Atmosphere Movement
Chapter 13
Workbook Activity 14
13.1: Air Pressure
Does air have weight?
______________________________________________________
Air pressure is not constant everywhere on Earth: there are areas
of high and low pressure. Why?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Air pressure can also be affected by:
a) ______________________________________________
-When air is warm, molecules are ________________________ apart. As a result, a given volume of air
will have ________________________ air molecules and a lower air pressure. The opposite is true of
cold air.
b) ______________________________________
-Water molecules push out
an equal volume of oxygen
and nitrogen (heavier than
water) in humid air
conditions, creating less
dense air and a lower air
pressure.
The differences in air pressure can be plotted on a weather map.
Isobar: Line joining points with the same atmospheric pressure.
High-Pressure Area (Anticyclones): Associated with fair weather as compression of air results in higher
temperatures and evaporation of water droplets (no cooling/condensation)
Low-Pressure Area (Cyclones): Associated with high winds and warm air rising to produce clouds,
precipitation, storms, etc.
Pressure Gradient: Pressure change ÷ Distance Covered
13.2: Factors Affecting Wind Movement
All of these processes described above contribute to the movement of air from ______________ to
_______________ pressure areas.
Ultimately, the differences in pressure are caused by the unequal heating of Earth’s surface by solar
radiation.
Earth’s winds do not travel in a straight line
because the planet’s rotation and the force
of friction allow a combination of three
forces to act on its direction:
a) __________________________________
-An inbalance in pressure acting on an air
mass produces a force driving the air from
high to low pressure areas.
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-The greater the pressure difference, the greater the wind
speed.
*Complete Activity 14.10
b) _____________________________________________
-Earth turns under moving objects, making them appear to
deflect away from their target.
-Moving object deflect to the right in the Northern
Hemisphere and the left in the Southern hemisphere.
Four basic rules of the Coriolis Effect are:
1. Deflection is always at 90 degree angles to the direction
of airflow.
2. Deflection affects only wind direction, not speed.
3. Deflection is affected by wind speed (stronger winds
produce greater deflection).
4. Deflection is strongest at the poles and non-existant at the
equator.
c) __________________________________________
-Friction slows wind speeds at Earth’s surface, but plays little
role in the upper atmosphere.
-Will friction have a greater effect on land or over the ocean?
__________________________________________________
__________________________________________________
-Upper atmosphere winds unaffected by friction flow parallel
to the isobars due to the competing effects of the pressure
gradient force and the coriolis effect. This produces
geostrophic winds and the jet stream.
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13.3: Highs and Lows
There are two types of pressure centres and
both provide important information about
future weather conditions:
a) ____________________________________
Wind flows into (convergence) a low pressure
centre (following the pressure gradient) and
deflects counter-clockwise due to the Coriolis
Effect.
Is air rising or falling in a cyclone? What does this mean for weather patterns in areas affected by the
low pressure centre?
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
If air is stacking up on itself above a low
pressure centre is the air pressure increasing or
decreasing?
_______________________________________
_______________________________________
_______________________________________
_______________________________________
b) _____________________________________
Wind flows out of (divergence) a high pressure
centre (following the pressure gradient) and
deflects clockwise due to the Coriolis Effect.
Is air rising or falling in an anticyclone? What does this mean for weather patterns in areas affected by
the high pressure centre?
_____________________________________________________
_____________________________________________________
_____________________________________________________
The weather map to the right was for January 2nd, 2014. What
weather conditions was Vancouver experiencing then?
____________________________________________________
____________________________________________________
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13.4 : Global Atmosphere Circulation
Remember, the primary cause of wind is the unequal heating of Earth’s surface! The atmosphere
attempts to balance these differences through transferring heat by the movement of air.
*Watch the video on Idealized Global Atmosphere Circulation.
Take your own notes on the
following terms from text
431-432:
ITCZ: ______________________________
__________________________________
__________________________________
__________________________________
Subtropical High: ____________________
__________________________________
__________________________________
__________________________________
Polar Front: ________________________
__________________________________
_____________________________________________________________________________________
Polar High: ____________________________________________________________________________
The above pattern is a generalization and there are exceptions to it. Below is one example:
1. _________________________________________
Large seasonal fluctuations in temperatures on continents generate
monsoons:
a) High pressure systems are created in the winter as the air above
continents is cool, causing air to flow out to sea.
b) Low pressure systems are created in summer as the air above
continents warm, causing air to flow inland.
Why do these seasonal fluctuations exist at the subpolar low (Northern
Hemisphere)?
__________________________________________________________
__________________________________________________________
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Interestingly, fluctuations in air temperatures over the course of a day can also create wind movements
similar to monsoons:
a) Land and Sea Breezes
*Watch the video on Land and Sea Breezes and Mountain and Valley Breezes.
b) Mountain and Valley Breezes
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Surface Processes and Hydrosphere Unit
Air Masses
Chapter 14
Workbook Activity 15
14.1: Air Masses
Weather patterns are caused by the movement of air masses:
___________________________________________________
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The characteristics of an air mass is determined by its source
region:
c: Continental Air Masses (dry air)
m: Maritime Air Masses (humid air)
P: Polar Air Masses (cold air)
A: Arctic Air Masses (cold air)
T: Tropical Air Masses (warm air)
These basic air mass types can be combined to describe the source region and characteristics of air
masses.
The characteristics of the air mass above a particular region determines the weather it experiences.
*Complete Activity 15.1
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14.2: Weather Fronts
Fronts are boundaries separating
different air masses.
What are the characteristics of the
air mass forced upwards?
____________________________
____________________________
____________________________
What are the properties of the air
mass that remains near Earth’s
surface?
____________________________
____________________________
_____________________________________________________________________________________
There are four different types of fronts:
*Watch the video on fronts while answering the questions below.
1. Warm Front
Warm air moves into an area
occupied by cold air.
What type of weather change
would you expect to see at warm
fronts?
____________________________
_____________________________
_____________________________
_____________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
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2. Cold Front
Cold moves into an area occupied by
warm air.
What type of weather change would
you expect to see at warm fronts?
_____________________________
______________________________
______________________________
______________________________
______________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
3. Stationary Front
Wind is parallel to the fronts, so they do not advance.
Some clouds and precipitation if overrunning (warm air moving
over cold air) occurs.
4. Occluded Front
A cold front overtakes a warm front.
Warm air is forced up = adiabatic cooling, clouds and
precipitation.
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The weather map to the right
was for January 12, 2014.
What front was Vancouver
experiencing then?
_______________________
What type of weather did
Vancouver have?
_______________________
_______________________
_______________________
______________________
______________________
*Complete Activity 15.2
14.3 : Midlatitude Cyclones
Using all of the information discussed in the Atmosphere
Unit, we can now better understand the weather
patterns in the middle latitudes (Florida to Alaska).
Weather here is primarily produced by midlatitude
cyclones, which are labelled L (low pressure centres) on
weather maps and form when cold polar air (cP) meets
warm tropical air (mT).
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1. _______________________________________________________________________
a) A stationary front between cP and mT air masses exists in the
midlatitudes (see map above).
b) Counter-clockwise circulation of air can occur, with warm air rising to the
north and cold air descending to the south (cyclogenesis)
c) Air is pulled to the centre of circulation (convergence) and forced
upwards. If divergence occurs at an equal level higher in the atmosphere a
cyclone will develop.
d) The movement of warm air and cold air around the low pushes the
cyclone west to east.
e) Eventually, the cold front will catch up with the warm front and an
occluded front will occur (cold air below warm air).
f) Once an occluded front occurs convergence fills the low pressure area and
the cyclone decays.
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2. __________________________________________________________________________________
*View the video on
Midlatitude Cyclones.
*Use text pages 452 to 453 to
explore this topic and complete
Activity 15.3 in lab book, pages
215 to 217.
3. ____________________________________________________________________________
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4.
______________________________
The life span and intensity of a
cyclone and anticyclone is controlled
by airflow in the middle to upper
troposphere (jet stream)
The jet stream moves west to east
between 120-210 km/hr and
separates the cP and mT air masses.
The amount of air that sinks into
anticyclones and rises out of cyclones
depends on how sharp the jet
stream’s trough is and how fast it is moving.
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