Transcript 20.1 Air Masses

 An immense body of air that is characterized by
similar temperatures & amts. of moisture at any
altitude
 As air masses move the characteristics of an air mass
change and so does the weather in the area over which
the air mass is moving.
 Source region – the area over which an air mass gets its
characteristics of temperature & moisture
 Named according to their source region
 In addition to their overall temperature, air masses are
classified according to the surface over which they
form
 Continental Polar (cP) – dry cool
 Continental Tropical (cT) – dry warm or hot
 Maritime Polar (mP) – form over water, cold
 Maritime Tropical (mT) – form over water, warm or
hot
 Much of the weather in N. America, esp. weather E of
the Rockies, is influenced by continental polar (cP) &
maritime tropical (mT) air masses
AIR MASS FOLDABLE
 When 2 air masses meet, a front is formed.
 Front is a boundary that separates 2 air masses
 Fronts can form btw any 2 different air masses
 Fronts are often associated with precipitation
 Classified according to the temperature of the
advancing front
 4 types: Warm, Cold, Stationary, Occluded
 Warm Front
 Forms when warm air moves into an area formerly
covered by cooler air
 Red line with red semicircles that point toward the
cooler air
 Cold Front
 Forms when cold, dense air moves into a region
occupied by warmer air
 Shown by blue line edged with blue triangles that point
toward the warmer air
 Advance quicker than warm fronts do
 Stationary Front
 The flow of air on either side of a front is neither toward
the cold air mass nor toward the warm air mass. It is
about parallel to the line of the front
 In that case the front does not move
 Occluded Front
 When an active cold front overtakes a warm front
 Develops as the advancing cold air wedges the warm
front upward
 Weather associated is typically complex
 Low pressures are shown by the letter L
 Middle-latitude cyclones are big centers of LP that
generally travel W to E and cause stormy weather
 Air moves in a counter-clockwise direction & in
towards the center
 Pg. 567-68 How does a Cyclone form?
 Bring on stormy weather
 Plays an important role in maintaining cyclonic &
anticyclonic circulation.
 More often than not, air high up in the atmosphere
fuels a middle latitude cyclone
 A storm that generates lighting & thunder
 Produce gusty winds, heavy rain, & hail
 Forms from a single cumulonimbus cloud and only
affects a small area OR by a cluster of cumulonimbus
clouds and impact a larger area
 US experiences about 100,000 a year
 Form when warm, humid air rises in an UNSTABLE
environment
 Violent windstorms that take the form of a rotating
column of air called a vortex. The vortex extends
downward from a cumulonimbus cloud
 Form in association w/ severe thunderstorms
(developing a mesocyclone)
 Mesocyclone – a vertical cylinder of rotating air that
develops in the updraft of a thunderstorm
 SPC (Storm Predication Center) monitors different
kinds of severe weather
 Whirling tropical cyclones that produce winds of at
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least 119 km per hr.
Most form btw 5 – 20 degrees N & S latitude
Develop most often in the late summer when water
temp. are warm enough to provide the necessary heat
& moisture to the air
The center is known as the eye
Can cause storm surges
Weakens when it moves over cool oceans AND even
greater when it moves over land
Category 1-5