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

Oceans (maritime) carry a lot of water vapor 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: 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: 1. Bringing those two characteristics together, the air masses may be described. For the following, identify the characteristics: cT: mT: cP: mP: cA:   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

Page 13 of ESRT lists 4 types of front and symbols The type of front created depends on the direction the air masses move and the way the air masses meet. In the US, our weather systems tends to move from west to east. The winds in a storm, tend to make a counterclockwise rotation. Page 13 of ESRT lists 4 types of front and symbols 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)

Precipitation happens at the front 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

Precipitation happens ahead of the front. 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

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. (Nor-easters, 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

Rising air expands and COOLS. Water vapor CONDENSES. 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