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