Air masses and fronts
• 1. An air mass is a wide-spread section of the troposphere with uniform temperature and humidity (moisture)
• 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.
Uwsp.edu
• 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 199-200Air 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 countriesBetween lawnsBetween 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, t-storms 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
explore.ecb.org
http://www.nc-climate.ncsu.edu/edu/k12/fronts/body
Warm front: side view
nauticed.org
http://www.ux1.eiu.edu/~cfjps/1400/fronts.html
Warm front: map overview
– 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.
gcel.com.mx
• 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.htm http://www.nc-climate.ncsu.edu/edu/k12/fronts/body
Occluded front: side view
physicalgeography.net
aos.wisc.edu
– 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. (Nor-easters, some tornadoes and t-storms)
allposters.com
Overview
http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1d.html
muhs.acsu.k12.vt.us
Stationary front
http://www.nc-climate.ncsu.edu/edu/k12/fronts/body
lewistonpublicschools.org
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/chapter20.cfm
• https://castlelearning.com/review/login/login.aspx
for fronts
