What is an air mass
7.E.1.5 (Wind & Climate) & 7.E.1.3 (Severe storms) C. Notes
large section of the lower troposphere that has the same weather throughout
Where do air masses form
over continents, icecaps or the ocean
How are air masses controlled
by patterns of heating and cooling over large areas of the Earth’s surface
Air masses
Maritime air mass – air mass over ocean
Continental air mass – air mass over land
Tropical air mass – warm & hot
Polar air mass - cold air near the surface
Arctic air mass – extremely cold
Types of air masses that affect US
Maritime tropical (mT) – air masses are warm, moist & usually unstable
 They can be associated with fog and low clouds as they moves northward
 Some originate in the subtropical Pacific Ocean
 Some originate over the Gulf of Mexico and Caribbean Sea
Maritime polar (mP) – air masses are cool, moist & unstable
 Some originate as continental polar air masses over Asia and move westward over
the Pacific
 Some originate from the North Atlantic and move southwestward toward the
Northeast States
Continental tropical (cT) – air masses are hot, dry & unstable at low levels and generally
stable aloft (upper-level ridge)
 originate in northern Mexico
 characterized by clear skies and negligible rainfall
Continental polar (cP) – air masses are cold, dry & stable
 marked by surface high pressure, cold temperatures, and low dew points
 originate over northern Canada and Alaska
What is the difference between
conduction, convection and
radiation
conduction – transfer of heat by touching
 only occurs in solids
 Example: pot cooking on a stove’s burner
Convection – transfer of heat through particles  warm particles rise, cool particles sink
 Circular motion
7.E.1.5 (Wind & Climate) & 7.E.1.3 (Severe storms) C. Notes
 Only occurs in liquids & gases
 Example: pot of boiling water
Radiation – transfer of energy as waves
 Example: sun warming Earth
How do the 3 types of heat
transfer affect Earth’s
atmosphere
The atmosphere is warmed by radiation and conduction and then is transferred
throughout the atmosphere by convection
What causes wind
Air flowing from high pressure to low pressure
Uneven heating and cooling of Earth’s surface
Types of wind
Local wind examples
 Sea breeze  air moving from ocean to land
o Occurs during day when land is warmer than water
 Land breeze  air moving from land to ocean
o Occurs during the night when water is warmer than land
Global wind examples
 Polar easterlies  cold, fairly weak winds blowing from east to west
 Doldrums  very calm air in a band over the equator
 Trade winds  warm, steady winds that blow back toward the equator in usually
clear skies
 Prevailing westerlies cool air, usually moving quickly toward the poles from west
to east in both hemispheres
What causes a pressure gradient
Island heats faster than water (land heats faster, water stays warmer longer) so the air
above the island becomes warmer
Molecules in air become further apart
 Air expands upward & outward
Expansion lowers the air pressure over the island
Cooler ocean air moves in toward low-pressure area over the island
 Called pressure gradient between ocean and island
 Speed of wind depends on pressure gradient
o The lower the pressure (hotter the island), the steeper the pressure
gradient  stronger wind
What is pressure-gradient force
Where are wind speeds very high
What is the jet stream
What direction does jet streams
flow
Coriolis effect affects wind
Force that makes the wind blow
Upper troposphere
 Jet stream located there
fairly narrow zone of very strong winds in the upper troposphere
 Separates warm from cold air
east to west
Rather than flowing directly from areas of high pressure to low pressure, as they would
on a non-rotating planet, winds and currents tend to flow to the right of this direction
north of the equator, and to the left of this direction south of the equator
7.E.1.5 (Wind & Climate) & 7.E.1.3 (Severe storms) C. Notes
This deflection is responsible for the rotation of large cyclones
What is a warm surface current
As ocean currents move westward along the equator, they absorb lots of solar energy,
heat up, and become warm currents
How do currants affect weather
Because ocean currents circulate water worldwide, they have a significant impact on the
movement of energy and moisture between the oceans and the atmosphere
Example of warm surface current
Gulf Stream
 One of the strongest known currents
 As the Gulf Stream approaches Cape Hatteras, North Caroling the cold current
that flows from the north separates it from the coast as warm Gulf Stream
waters from the south (Florida) combine with the cold winds a dense
concentration of fog forms along with an immense heat transfer causing
atmospheric storms to intensify in this region
What is a storm
natural disturbances in the atmosphere that involve air pressure, clouds, precipitation,
and strong winds
7.E.1.5 (Wind & Climate) & 7.E.1.3 (Severe storms) C. Notes
Major types of storms
Thunderstorms
 known as electrical storms
 brief, intense storms that affect a small area
 characterized by the presence of lightning and thunder
 produced rapidly when rising air causes cumulus clouds to build upward into a
thunderhead
 are usually accompanied by strong winds, heavy rain and sometimes snow, hail
or no precipitation at all
 cloud type associated with thunderstorms are cumulonimbus
Hurricanes
 huge, rotating storms that form over the ocean near the equator
 produce very strong winds, heavy rains, and large, powerful waves and can
cause severe flooding and damage from strong winds
Tornadoes
 violently whirling winds sometimes visible as a funnel-shaped cloud
 produced by severe thunderstorms
 Spiraling high winds and extremely low pressure are the unique features
Winter storms
 are associated with quickly moving cold fronts and they can produce high
winds, very low temperatures
 possible blizzards
 ice storms and large accumulations of snow
Floods
 occur when an area is inundated with water
 most often associated with hurricanes and thunderstorms