110TH AVIATION BRIGADE
UNITED STATES ARMY AVIATION WARFIGHTING CENTER
Fort Rucker, Alabama
November 2007
File No. 2/5/9/9E-0217-3
STUDENT OUTLINE
ATMOSPHERE AND AIR MASSES
AVIATION WEATHER
TERMINAL LEARNING OBJECTIVE: Acting as an aviator and when given an IFR or VFR flight mission and
available weather information, the student will plan the flight for weather considerations in accordance with (IAW)
AR 95-1 and FM 1-230.
ENABLING LEARNING OBJECTIVE: Given pertinent information about the atmosphere, the student will identify
the composition and its effects on weather IAW FM 1-230.
1. Atmosphere.
a. Definition: a great envelope of air (gases) that surrounds the earth and rotates with it. Approximately
one-half the air by weight is within the first 18,000 feet.
b. Composition: dry air--nitrogen 78%, oxygen 21%, other gases 1%.
c.
Natural air: dry air plus various amounts of water vapor and condensation nuclei.
(1) Water vapor is an invisible gas and is found mostly below 30,000 feet.
(2) Condensation nuclei consist of dust, smoke, and salt (hygroscopic). Salt particles attract water vapor.
EXAMPLE: Salt shaker on a humid day.
ENABLING LEARNING OBJECTIVE: Given pertinent information about the atmosphere, the student will identify
its layers, height, and in which layer weather occurs IAW FM 1-230.
2. Layers of the atmosphere.
a. Troposphere--closest to the earth.
(1) Height at equator approximately
60,000 feet, hot air is less dense and rises.
(2) Height at poles approximately 25,000
feet, cold air is more dense and descends.
b. Stratosphere--above the troposphere.
c.
Weather only occurs in the troposphere.
(1) Water vapor.
(2) Condensation nuclei.
d. Tropopause--the boundary zone between the troposphere and the stratosphere.
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ENABLING LEARNING OBJECTIVE: Given pertinent information about the atmosphere, the student will identify
atmospheric circulation, Coriolis force, and the three-cell theory IAW FM 1-230.
3. Atmospheric circulation.
a. Circulation.
(1) The movement of air over the surface of the earth is caused by uneven heating.
(2) Changes in temperature and density causes air to be warmed at equator and rises, flows towards
poles, air is cooled at poles and descends, flows toward equator.
b. Conditions affecting atmospheric circulation (three-cell theory).
(1) Uneven heating of earth's surface, land heats and cools rapidly, water retains temperature.
(2) Rotating earth--Coriolis force.
(a) Definition--force developed by the
unequal speed of rotation of the
earth’s surface. Speed is greater at
the equator than at the poles causes
a deflection of the wind. Force is
greater at the poles, zero at the
equator.
(2) Northern hemisphere--to the right.
(3) Southern hemisphere--to the left
(3) Earth tilted on its axis—causes
seasonal changes.
c.
The United States is situated between the 30 latitude and 60 north latitude. High- and low-pressure
systems in the United States generally move in conjunction with the prevailing winds.
ENABLING LEARNING OBJECTIVE: Given pertinent information about heat energy, the student will identify the
four types of heat transfer IAW FM 1-230.
4. Heat energy.
a. Definition--an expression of molecular activity within a substance.
b. Methods of heat transfer.
(1) Radiation--transfer of heat by electromagnetic waves.
(a) Insolation--incoming from the sun (short wave).
(b) Terrestrial--outgoing from the earth (long wave).
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(2) Conduction--transfer of heat by physical contact. Heat always travels from warm to cold.
(3) Convection--transfer of heat by way of a gas in a vertical movement.
(4) Advection--horizontal movement and is somewhat greater than vertical movement.
ENABLING LEARNING OBJECTIVE: Given pertinent information about the temperature, the student will identify
its relationship with altitude change, to include temperature inversions, IAW FM 1-230.
5. Temperature.
a. Definition--a measurement of the level of intensity of heat energy (the degree of "hotness" or "coldness")
measured in degrees Celsius.
(1) Warmest temperatures found near the earth's surface.
(2) Decreases with altitude.
(3) Change in temperature with altitude is called lapse rate, standard for temperature 2C/1,000 feet.
(4) Observed Lapse Rate (OLR) is the actual change in temperature with altitude.
b. Temperature inversions—when temperature increases with altitude rather than decreases.
(1) Nocturnal--cool clear night.
NOTE: Overcast skies (greenhouse effect) would prevent nocturnal inversions.
(2) Frontal--cold air lifts warmer air.
ENABLING LEARNING OBJECTIVE: Given pertinent information about air masses, the student will identify its
characteristics, classification, stability, and movement IAW FM 1-230.
6. Air masses.
a. Definition--a large body of air whose physical properties (temperature and moisture) are horizontally uniform.
b. Size--many hundreds of miles.
c.
Formation--source region and takes on characteristics of region.
(1) Land areas--air becomes dry.
(2) Water areas--air becomes moist.
(3) Physical characteristics--of moisture and temperature acquired in source region.
d. Semi-permanent pressure areas.
(1) Caused by variations in the earth's physical characteristics.
(a) High pressure tends to form over cooler areas, land in winter and oceans in summer.
(b) Winter and summer months will cause pressure systems to vary slightly in latitude.
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(2) Pressure systems (air masses) that control weather over the United States.
(a) North American High (Canada). Cold, dry air from Canada moving south, usually originates
within the Arctic Circle.
(b) Siberian High (Siberia). Cold dry air from Siberia, changes to moist air over the North Pacific
Ocean and enters the northwestern US as cold, moist air.
(c) Bermuda High (Bermuda Islands) brings warm, moist air from the Gulf of Mexico and causes
precipitation in the summer months and fog in the winter.
e. Most air masses are designated as high pressure systems and follow a path called air mass trajectory.
(1) Cold air masses move south out of their source regions.
(2) Warm air masses move north out of their source regions.
(3) Air mass characteristics change as they move along their trajectory.
f.
Classification code.
(1) Continental--formed over land--lower cased “c,” moisture content low.
(2) Maritime--formed over water--lower cased “m,” moisture content high.
(3) Temperature--upper cased letter.
(a) A--source region, arctic, temperature is coldest. (70 to 90 N)
(b) P--source region, polar, temperature is cold. (40 to 60 N)
c) T--source region, tropical, temperature is warm. (10 to 30 N)
(d) E--source region, equatorial, temperature is warmest. (0 to 10 N)
(4) These symbols are combined in the following manner to describe air masses:
SYMBOL
(a) cA
SOURCE &
SURFACE
Continental Arctic
TEMPERATURE &
MOISTURE
Coldest, dry
(b) cP
Continental Polar
Cold, dry
(c) mP
Maritime Polar
Cold, moist
(d) mT
Maritime Tropical
Warm, moist
(e) cT
Continental Tropical
Warm, dry
(f) E
Equatorial
Warmest, moist
(5) Stability--lower cased letter (thermodynamic classification).
(a) w--stable, warmer than the surface. WARM (w type) MARITIME AIR MASSES will normally
have--
1.
Horizontal development type clouds and possible fog.
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2.
Low ceilings.
3.
Poor visibility.
4.
Smooth, stable air with little or no turbulence.
5.
Occasional light continuous drizzle or rain.
(b) k--unstable, colder than the surface. COLD (k type) MARITIME AIR MASSES will normally have1.
Vertical development type clouds.
2.
Generally good ceilings (except within precipitation areas).
3.
Excellent visibility (except within precipitation areas).
4.
Pronounced air instability (turbulence) in lower levels due to convective currents.
5.
Occasional local thunderstorms, heavy showers, hail, or snow flurries.
(c) Continental air masses are associated with good flying conditions, to include clear skies, good
visibility, and little or no precipitation. Two exceptions are as follows:
1.
Intense surface heating may produce strong turbulence with associated gusts and
blowing dust or sand (cTk).
2.
with drizzle or snow.
Movement of cold, dry air over warm water may produce dense fog or low overcast skies
(6) Examples of combined air mass designations.
SYMBOL
SOURCE & SURFACE
THERMODYNAMIC
CLASSIFICATION
(a)
cPk
Continental Polar Cold
Colder than surface
(b)
mPk
Maritime Polar Cold
Colder than surface
(c)
mTw
Maritime Tropical Warm
Warmer than surface
(d)
cTk
Continental Tropical Cold
Colder than surface
g. Air mass movement.
(1) cP.
(2) mP.
(3) mT.
(4) cT.
ENABLING LEARNING OBJECTIVE: Given pertinent information about a type of air mass, the student will
identify the typical weather associated with it IAW FM 1-230.
7. Typical air mass weather for summer and winter.
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a. Continental polar--cP.
(1) Summer.
(a) Scattered vertical developed clouds (daytime) (cPk).
(b) Clear stable air at night (cPw).
(2) Winter.
(a) Clear skies (cPk or cPw).
(b) Air unstable at surface (cPk).
b. Maritime polar--mP.
(1) Summer.
(a) Pacific coast.
1. Vertical developed clouds and scattered showers (daytime) (mPk).
2. Fog and low horizontal developed clouds (night time) (mPw).
(b) Northeast coast is not affected by mP air mass in summer.
(2) Winter.
(a) Pacific coast.
1. Horizontal developed clouds (mPw).
2. Vertical developed clouds and extensive showers along mountain slopes because of
orographic/mechanical lifting over coastal mountains.
(b) Northeast coast.
1. Low horizontal developed clouds (mPw).
2. Light continuous precipitation (mPw).
3. Strong winds.
c.
Maritime tropical--mT.
(1) Summer.
(a) Horizontal developed clouds early morning (mTw).
(b) Vertical developed clouds (mTk).
(c) Widely scattered thunderstorms (mTk).
(2) Winter.
(a) Fog and horizontal developed clouds (mTw).
(b) Extent of fog and clouds depends on surface versus air temperature
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d. Continental tropical--cT. (Low)
(1) Primarily in Mexico, Arizona, and Southeast California area.
(2) High temperature--low humidity.
(3) Flying bad due to turbulence.
(4) Occasional dust storms to 10,000 feet or higher.
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North American
High
Icelandic
Siberian
High
Bermuda
High
Pineapple
Express
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