Download Chapter 12 METEOROLOGY

METEOROLOGY
Ch. 12
Standards
• SES5. Students will investigate the
interaction of insolation and Earth systems
to produce weather and climate.
– b. Explain the relationship between air
masses and the surfaces over which they
form.
– c. Relate weather patterns to interactions
among ocean currents, air masses, and
topography.
12. 1 The Cause of Weather
Weather vs. Climate
Meteorology is the study of atmospheric phenomenon.
Short term variations in the
current state of the atmosphere
that affect the environment and
life on Earth are called weather
Climate is the long-term
average variations in
weather for a particular
area.
Heating Earth’s Surface
• The sun is always heating a portion of Earth’s
surface.
Why is a January day warmer in
Miami than in Detroit?
Why, when it is summer in
America is it winter in Australia?
Why do the North & South
poles get 6 months of daylight
and 6 months of darkness?
ANSWER: Because the Earth TILTS
In this illustration the same amount of solar radiation heats
Miami more than Detroit because Miami is closer to the
equator, which gets the majority of solar radiation.
Air Masses
• Air over a warm surface is heated by conduction.
• This heated air rises because it is less dense than the
air surrounding it.
• This can take place over thousands of square kms
over days or weeks.
• An air mass is a large volume of air that has the same
characteristics (such as humidity and temperature) as
its source region (the area over which it forms).
• Air masses are classified according to where they
form.
5 Types of Air Masses
• Tropical Air Masses
1. Maritime tropical (mT): tropical bodies of water like Gulf of
Mexico or Caribbean
2. Continental tropical (cT): Southwestern US
• Polar Air Masses 3. Maritime polar (mP): North Atlantic or North Pacific oceans
• Bring heavy rains to west coast of US in winter
4. Continental polar (cP): interior of Canada or Alaska
• Winter: carries frigid air south
• Summer: provides relief from from hot, humid weather
5. Arctic (A) Air Masses • Source: above 60o N latitude
• Receive virtually no solar radiation in winter
• Bring coldest winter temperatures
12.2 Weather Systems: Fronts
• When different air masses collide, they DO NOT MIX.
• A collision of two air masses
forms a dramatic weather change
called a front.
• There are four types of fronts.
Cold Front
• When cold, dense air displaces warm air, it
forces the warm air, which is less dense, up
along a steep slope.
• Brings intense
precipitation and
sometimes
thunderstorms.
Warm Front
• Advancing warm air displaces cold air.
• Causes widespread light precipitation.
Stationary Front
•When two air masses meet but neither
advances, the boundary between them stalls.
•Light winds and precipitation
Occluded Front
• Sometimes a cold air mass moves so fast it
overtakes a warm front and forces warm air
up.
• Advancing cold air mass collides with cold air
mass in front of the warm front.
• Strong winds & heavy precipitation.
Pressure Systems
•
•
•
•
Sinking air = high pressure
Rising air = low pressure
Air flows from high to low pressure
Low Pressure System
H
L
– Air rises, spirals toward the center and up
– As it rises, it cools & condenses into clouds = cloudy
weather & precipitation
• High Pressure System
– Sinking air moves away from
the system’s center when it
reaches Earth’s surface
– Fair weather (like in
subtropical ocean climates)
Global Wind Systems
• The direction of Earth’s winds are influenced
by Earth’s rotation.
• The Coriolis Effect results in a curved flow of
wind & water.
• The Coriolis Effect + the unbalanced heating
of Earth = distinct global wind systems that
move warm air from the tropics & cold air
from the poles
• There are three basic wind systems in each
hemisphere, the polar easterlies, prevailing
westerlies, and trade winds.
Polar Easterlies
• 60oN latitude and the North Pole and 60oS
latitude and the South Pole are the polar
easterlies.
• Weak, sporadic, cold
wind that moves in an
easterly direction away
from each pole.
Prevailing Westerlies
• Located between 30oN and 60oN, and between
30oS and 60oS
• Steady winds that originate from the west and
blow toward each pole
• Move much of the
weather across the
United States
Trade Winds
• Between 30oN and 30oS (including the
equator) are two circulation belts of wind
known as trade winds.
• Air moves toward the equator
(intertropical convergence
zone ITCZ) in an easterly
direction, rises, and moves
back towards 30o latitudes.
(horse winds)
Air Pressure
• Air pressure is due to the weight of the
atmosphere and is equal to the force/area or
N/m2. The usual unit is 100 N/m2 or 1 millibar
(mb).
•At sea level air pressure is
1000 mb. Increases in
elevation mean decreases in air
pressure, as there is less air
above you.
•There are less oxygen
molecules when there is less
density. That is why we say the
air on mountaintops is ‘thinner’
and makes it harder to breathe.
Jet Stream
• The difference in air pressure causes wind.
• A jet stream is a narrow band of fast wind that
results from temperature differences of air
masses at wind zone boundaries.