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) give
Air 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 ‘c’ for
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 source region,
or area where it formed. For
each of the following locations
create our air mass (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:
1. how quick the change is and 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. This is what caused
last week’s tornadoes!!!
2. 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