GEOG220 Chapter Notes - Chapter 8: Air Mass (Solar Energy), Stratus Cloud, Atmospheric Circulation
18 May 2018
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8.3 Air Mass Modification
Describe the process by which traveling air masses are modified and discuss two examples
● After an air mass forms, changes in atmospheric circulation eventually cause it to
migrate for the area where it acquired its distinctive properties to a region with different
surface characteristics
● Changes can be made to air mass that completely change original identity of air mass
● cA or cP air mass moves over ocean in winter, it undergoes considerable change
○ Evaporation from water surface rapidly transfers large amount of moisture to
once dry continental air
○ Since the underlying water is warmer than the air above, air is heated from below
which can lead to instability and vertically ascending currents that rapidly
transport heat and moisture to higher levels - can form unstable mP air mass
● When an air mass is colder than the surface over which it is passing, as in the preceding
exame, the lowercase letter k may be added after air mass symbol
● If air mass is warmer than lowercase w is added
○ These k or w suffixes does not mean that the air mass itself is cold or hot, instead
means that the air relatively is cold or warm in comparison to underlying surface
its traveling over
● The k or w gives an indication of the stability of an airmass - the weather that might be
expected weather
● An air mass that's cooler than the earth’s surface is going to be warmed in its lower
layers -> causes greater instability that may see the ascent of heated lower air and
creates the possibility of cloud formation and precipitation
○ A k air mass characterized by cumulus clouds, and if precipitation occurs
normally shower or thunderstorm
● The opposite would give stratus clouds if any, and if any precipitation it would be light
○ Since lack of vertical movements, smoke and dust often become concentrated in
lower layers and cause poor visibility
● Cyclones, anticyclones or topography can also affect stability of an air mass
○ Called mechanical or dynamic modifications
● Air mass going over highlands, or descends the leeward side of a mt barrier, also
anticyclones makes air more stable
8.4 Properties of North American Masses
Summarize the weather conditions associated with each of the air masses that influence North
America during the summer and winter
Air
Mass
es
Source
Region
Temp and
Moisture
Characteristics in
SOurce Region
Stability in
source
region
Associated Weather
cA
Arctic
Bitterly cold and
stable
Cold spells in winter
