Chapter Eight - Test Three Flashcards
What is an Air Mass?
An immense “body” of air (thousands of km2 across, and several km thick) dominated by High Pressure whose: Thermal and moisture properties remain homogenous in any direction within the air mass.
When the air mass moves out of its region of origin, it will carry these T and Td characteristics with it
Thermals property: Temperature (T)
Moisture property: Dewpoint (Td)
Source Regions
Air masses develop over regions of uniform geography, usually flat
regions of similar composition (i.e. sand, water, ice) that are:
Conducive to the formation of high pressure
Examples: Gulf of Mexico
Deserts of Mexico
Tundra of northern Canada
Atlantic and Pacific Ocean
The longer an Air Mass remains stationary over its Source Region, the more likely it will…
acquire the thermal and moisture properties of the surface
Classifying Air Masses
Depends on the latitude and nature of the underlying surface.
Classifying Air Masses
For latitude, we designate:
arctic, polar or tropical, which determines thermal properties
Classifying Air Masses
For surface, we designate:
continental or maritime, which determines moisture properties
Air Mass
cA
cP
cT
mT
mP
What about Basic Thermal or Moisture properties?Basic Thermal, Moisture Properties cA Very cold Dry (winter only) cP Cold Dry cT Hot Dry (summer only) mT Warm Moist mP Cool Moist
Remember that all four air mass types are characterized by ____
high pressure
The typical movement of the four major air
masses is controlled by the:
Jet Stream
Continental Polar (cP) and Continental Arctic (cA) Air Masses
Characterized by very cold (cA) or cold (cP) and dry air
North American Air Masses are characterized by very cold (cA) or cold (cP) and dry air
Cold : because of the long nights in the high latitudes (i.e. little solar radiation)
lack of water vapor in the air results in maximum, almost continuous radiational cooling
Dry : because the air originates over land and/or frozen ArcticOcean and because cold air holds very little water vapor
cA (form over Arctic Basin) and cP (form over northern Canada) air masses originate over flat snow/ice covered areas and generally move south-southeast into the US, responsible:
- coldest air in the winter: “Siberian Express” (Box 8.1)
- Lake Effect snow storms (Box 8.2)
Maritime Polar (mP) Air Masses
Originate over the northern Pacific and Atlantic Oceans
North American Air Masses are characterized by cool and moist air (mP)
Cool : because it originates over the northern oceans, which are always cool (but never frozen)
Moist: because the air originates over open oceans where water vapor is plentiful
Pacific mP Air Masses
Generally move east into the western and central US
- Generally keeps the Pacific Coast states cool (even in summer) - The moisture gets “squeezed” out by the various mountain ranges in the western states (Fig 15.12)
so that the air mass becomes drier by the time it reaches the central states
Atlantic mP Air Masses
Move southwesterly into the US, generally east of the Appalachian Mountains from North Carolina to Maine
- Influence is less frequent, generally in winter and spring - associated with Nor’easters
Maritime Tropical (mT) Air Masses
mT air masses originate over the Atlantic, Gulf of Mexico and Pacific
North American Air Masses are characterized by warm and moist air (mT)
Warm: because it originates over the southern oceans (Gulf), which are always warm
Moist: because the air originates over open oceans where water vapor is plentiful
Half days in NC are dominated by
Gulf of Mexico (Atlantic) mT Air
Gulf of Mexico (Atlantic) mT Air:
during the winter, the mT air mass usually confined to the deep south, however, during the summer it will dominate the weather east of Rocky Mountains.
Gulf of Mexico (Atlantic) mT Air is responsible for:
- Oppressively high temperatures and humidity (i.e. High Apparent Temperatures)
- The majority of Precipitation that falls on the eastern half of the U S originates from mT air from the Gulf (Fig 8.9)
It is the air mass found most frequently over North Carolina.
Pacific mT Air
Influence is usually confined to the southwest U.S.
- Associated with “Monsoonal” thunderstorms in Arizona and New Mexico
Continental Tropical (cT) Air Masses
cT Air masses generally originate in Mexico and move north into the southwest and south central US
- Occurs only during the summer months - Responsible for devastating droughts
It is the air mass found LEAST frequently over North Carolina.
North American Air Masses are characterized by hot and dry air (cT)
Hot and dry: because it originates over the desert region of northern Mexico which receives strong radiation and contains little water
