Download Air Masses: cP

Air Masses
Classified by temperature and humidity
P = polar
T = tropical
A = Arctic
m = maritime
c = continental
Air masses: cA
Continental Arctic (cA) Air Masses
• Alaska, Canada and Asia origin
– Air cools with little sunlight, lots of reflection
• Cold and dry
– -30 C, <0.24 g/kg)
• Inherently stable, dense
Fig. 3, p. 294
Air Masses: cP
Continental polar (cP)
Source region: N. Canada, Alaska, Asia
Dry, cold, stable
• Less extreme than cA
• More snow than cA
– Higher frost point
Stepped Art
Fig. 11-4, p. 292
cP
cP Air Migration and
Modification
cP and lake effect snow
Topic: Lake Effect Snow
cP air passes over unfrozen lake,
absorbs moisture and drops snow on
leeward side of lake
cP and lake effect snow
Recipe: cold, dry air +
warm water
Impact
cP: winds from W, NW
Need large body of
water to retain warmth
Water must have been
warm recently, while air
is below freezing
• November: yes
• February: no
• July: no
Fig. 2, p. 291
Air masses: mP
Maritime Polar (mP) Air Masses
Upper latitude ocean origin
•
•
•
•
Source region: North Pacific, North Atlantic
Air cools due to little insolation
Warmed by ocean currents
Water supplied by evaporation of warmer ocean
water
Cool, moist, unstable
Affect Pacific Northwest
Affect Northeast US as nor'easters
Air masses are modified as they move
mP: dry in Nevada, Utah, Colorado
Stepped Art
Fig. 11-8, p. 295
Nor’easter, March 1994
Nor’easter, March 1994
Nor’easter, March 1994
Nor’easter, January 1986
Pattern
Low P in SE US
Low moves up
coast
Cyclonic
circulation moves
mP airmass on
shore
Convergence
leads to uplift
leads to snow
Air Masses: mT
Martime tropical (mT)
Source region: low latitude ocean
• Gulf of Mexico, Caribbean, SE Pacific
Wet, warm, unstable
Spring: mT vs. mP
Air Masses: cT
North American cT
Source Region: SW US, Mexican Plateau
Hot, dry, stable
• Mountains trigger uplift, clouds
Fig. 11-12, p. 297
Air masses
Air mass boundaries
Fronts
Boundaries between air masses with different
temperatures
• Usually also different water content
Warm front = warm air advancing
Cold front = cold air advancing
Stationary: not moving
Occluded: cold-cold at surface, warm upper level
Dry lines
Boundary between similar temperatures but unlike
humidity
Dry air advancing to E
Air mass boundaries
The four fronts
Air mass boundaries
Air mass boundaries
Fronts
Transition zone between two air
masses of different densities
Identification on Charts
1.
2.
3.
4.
5.
Sharp temperature change
Sharp change in dew point
Shift in wind direction
Sharp pressure change
Clouds and precipitation
Fig. 11-13, p. 298
Frontal systems
Form around surface
low, upper level
divergence
Study materials
Friday: finish chapter 11
Questions for review: 1-11, 13-16, 18
Questions for thought: 1, 6, 8