Air masses and fronts
• 1. An air mass is a widespread section of the
troposphere with
uniform temperature
and humidity (moisture)
Uwsp.edu
• 2. The source region is
the geographic location
the air mass developed
over.
– If air settles over one
location for a long time,
it develops the
characteristic
temperature and
moisture of the area.
• Because temperature
changes so much with
latitude, tropical areas
are warm and polar are
cold.
• Oceans (maritime) carry
a lot of water vapor
• On land, (continental)
there is little water and
the air is dry.
blueollie.wordpress.com
Page 13 ESRT uses symbols for the air masses
• Dry air is small ‘cf’ or
continental
• Moist air is small ‘m’
for maritime
• Cold air is ‘P’ for Polar
and REALLY cold air is
‘A’ for arctic.
• Warm air is ‘T’ for
tropical
Geography.hunter.cuny.edu
And to practice:
• 1. Bringing those two
characteristics together, the air
masses may be described. For
the following, identify the
characteristics:
cT:
mT:
cP:
mP:
cA:
• 2. The characteristics of the air
mass is due to the
__________________ region, or
area where it formed. For each
of the following locations create
our ______ _________ (and
weather), identify the
characteristics of the air, using
the terms continental, maritime,
tropical, arctic and polar.
Gulf of Mexico:
Central Mexico:
Great Plains (winter):
Central Canada:
Northern Atlantic:
Review book Chapter 8 pages 199-200
Air masses and polar fronts:
http://www.classzone.com/books/earth_science/terc/navigation/chapter20.cfm
https://castlelearning.com/review/login/login.aspx for air masses
Fronts: the boundary between two air masses
• A boundary describes
where two different
things meet.
Between countries
Between lawns
Between air and land.
A frontal boundary is where
two different air masses
meet. Energy is exchanged.
• Fronts bring a change in
weather.
• One type of air mass
pushes in and replaces
another one.
• “Bad weather” (storms
and precipitation)
occurs at fronts.
• How severe the storm is depends on:
– how quick the change is
– The differences between the 2 air masses:
• a REALLY warm, moist air mass meeting a REALLY cold, dry air mass
will produce dramatic weather/storm.
– How much moisture is in the warm air mass.
weather.thefuntimesguide.com
The type of front created depends on the direction the
air masses move and the way the air masses meet.
• Page 13 of ESRT lists 4
types of front and
symbols
• In the US, our weather
systems tends to move from
west to east.
• The winds in a storm, tend
to make a counterclockwise
rotation.
scoutweatherbadge.wordpress.com
Cold Fronts
• Side view:
physicalgeography.net
geography.hunter.cuny.edu
Cold front overview
– Cold front, in which
heavy cold air replaces
light, warm air .
– The effect is tall,
dramatic cumulonimbus
clouds, lots of wind, and
brief and intense
precipitation. (hail, tstorms and even
tornadoes)
• Clouds form at fronts
because warm, moist air
is pushed up at the
boundary by the heavier,
colder air mass.
• Clouds form as rising air
cools to the dew point
temperature and water
vapor condenses around
condensation nuclei,
such as soot or ash.
• Precipitation happens at
the front
http://www.nc-climate.ncsu.edu/edu/k12/fronts/body
explore.ecb.org
Warm front: side view
nauticed.org
http://www.ux1.eiu.edu/~cfjps/1400/fronts.html
Warm front: map overview
gcel.com.mx
– Warm front, in which
warmer air replaces
colder air. The effect is
cirrus and stratus clouds,
steady precipitation that
may last for a day or
two.
– Usually, the warm air
has more moisture.
– The warm air is pushed
up at the frontal
boundary, causing clouds
to form.
• The wedge-shape front
is caused by the warm
air slowly pushing up
along the boundary.
• Precipitation happens
ahead of the front.
http://elearning.stkc.go.th/lms/html/earth_science/LOcanada7/706/3_en.ht
m
http://www.nc-climate.ncsu.edu/edu/k12/fronts/body
Occluded front: side view
physicalgeography.net
aos.wisc.edu
allposters.com
– Occluded front, in which a cold air mass wraps
around a warm air mass, actually lifting the air off
the ground.
– This causes a REALLY dramatic change in weather,
intense winds and violent precipitation. (Noreasters, some tornadoes and t-storms)
Overview
muhs.acsu.k12.vt.us
http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1d.html
Stationary front
lewistonpublicschools.org
http://www.nc-climate.ncsu.edu/edu/k12/fronts/body
http://www.windows2universe.org/earth/Atmosphere/html
• Stationary fronts may last
for days because the 2 air
masses just don’t really
move. Usually, the
characteristics are similar to
the warm front, just
prolonged.
• Again, it is the warmer air that is
pushed up because it is less
dense.
• Why clouds???
• Rising air expands and
COOLS.
• Water vapor
CONDENSES.
http://www.geog.ucsb.edu/~joel/g110_w08/lecture_notes/midlat_surface/
midlat_surface.html
Previous page: Polar front development
• Review book
chapter 8 pages
200-203 and
questions 14-21.
•
http://www.classzone.com/books/
earth_science/terc/navigation/cha
pter20.cfm
•
https://castlelearning.com/review/
login/login.aspx
for fronts