Transcript Lect17_airmass

Chapter 8
Air Masses
What is air mass?
An immense body of air, usually thousand kilometers or more across
and perhaps several kilometers thick, which is characterized by
relatively homogeneous physical properties (in particular temperature
and moisture conetent) at any given altitude.
Movement
of a
Cold and Dry
Air Mass
Brings
Winter Weather
Air Mass
Source
Regions
Two criteria for an ideal
source region:
1. It must be an extensive
and physically uniform area.
2. The atmospheric
circulation must be relatively
stagnant so that air can stay
over an area long enough
to come to some measure
of equilibrium with the
surface.
Air Mass
Modification
Continental Polar and Continental Arctic Air Mass
1. Bitterly cold and very dry
2. Very stable
3. Sweep rapidly with relative ease far southward and affect
much of the central and eastern US.
Lake-Effect Snow: Cold Air over Warm Water
The Siberian Express
Pacific Maritime Polar Air Mass
Maritime Polar Air Mass from the North Atlantic
Only occasionally affects the weather of North America
Nor’easter
Maritime Tropical (mT) Air Mass
Atlantic mT Air Mass (originated from the Gulf-Caribbean-Atlantic region)
mT Air Moves over Heated Land Resulting
in Cumulus Development and Showers
North Pacific mT Air