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GLOBAL FORCES NOTES
UNIT 9 BACKGROUND INFORMATION
• Global forces are working together to create general patterns of weather
phenomenon. The sun’s energy heats the Earth unevenly. This uneven
heating creates a convection current that generally moves cold air from
the poles to the equator.
• However, the rotation of the Earth causes the wind to move in a curved
path. This phenomenon is called the Coriolis Effect. The convection
cells and the Coriolis effect work together to create global winds that
blow from the east in the tropics, from the west in temperate latitudes,
and from the east in near the poles.
• In the United States this explains why our weather fronts move from the
west coast to the east coast and why hurricanes move toward our
southern shores from the east. These relatively constant winds also
influence the movement of ocean water, creating a weather pattern
called El Niňo. In addition to global weather patterns there are some
localized events such as tornadoes and hurricanes.
3 Ways Heat is Transferred
1. Conduction – transfer of
heat through direct
contact
(ex. the handle of a metal
spoon becomes hot when
placed in a bowl of soup
even though it is not
touching the soup).
2. Convection – the transfer
of heat by the movement
of a liquid or gas
(ex. boiling water in a pot,
magma in the earth’s
mantle, hot air rises cold air
sinks, wind).
3. Radiation – the transfer of
heat through matter or
space (ex. a space heater
warms a room, the sun
warms the earth)
Radiant Energy
• The sun does NOT heat the earth
evenly.
• The poles receive less sunlight.
• The equator receives the most
direct sunlight.
The Coriolis Effect
• Wind and water move in
a curved pattern due to
the rotation of the earth.
• The earth rotates
counterclockwise, that is
why water and winds in
the northern hemisphere
will move clockwise
(west).
• (The windless, rainy
zone near the equator is
called the doldrums)
•
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crl
s.rxml
El Nino
• An abnormal warming of surface ocean waters in the
eastern tropical Pacific ocean, causing trade winds to
weaken or reverse.
• It is first noticed off the coast of Peru, when there is a
build up of warm water off of S. America.
• It prevents the upwelling of cold water. When cold water
upwells, it brings nutrients to the surface, for fish to eat.
Normal
Conditions
El Nino
Conditions
La Nina
• The winds blowing across the Pacific
are stronger than normal.
Ocean Current
• The steady flow of surface water in a
specific direction.
There are a number of ocean currents found
around the Earth. A current is like a vast
river within the ocean, flowing from one
place to another. These currents are caused
by differences in temperature, differences in
salinity, and by wind. Currents are
responsible for a vast amount of movement
of the water found in the Earth’s oceans.
Climate
• The weather pattern in a region, over
a long period of time.
Weather
• The state of the atmosphere
at a specific time and place.
Air Mass
• A large body of air that has properties similar to the part
of Earth’s surface over which it develops.
• (Ex: An air mass that develops over the tropics will be
warmer than one that develops at the poles.)
• Air masses will move from the poles down to the
equator, because cold air is more dense, and sinks.
Warm air is less dense. The warmer it is, the quicker it
will rise.
Fronts
• A boundary between 2 air masses that
have different densities, moisture, or
temperatures.
• Cold front – cold air moves underneath
warm air suddenly. Extreme temp.
differences will cause large thunderstorms
or tornadoes to form.
• Warm front – Warm air skims over colder
air. Leads to wet weather.
• Occluded front – Involves 3 air masses of
different temps. Ex. Cold air moves into
warm air with cold air on the other side of it.
C-W-C
• Stationary front – When a boundary
between air masses stops moving. May
stay in the same place for several days,
bringing wind and rain.
Picture of a Occluded front with
two cold air masses and one
warm air mass.
Tornado
• A violent, whirling wind that moves in a narrow path
over land. (pg. 473)
Fujita Scale (Tornadoes)
F Scale #
Intensity Phase
Wind Speed
Type of Damage Done
F0
Gale Tornado
40-72 mph
Some damage to chimneys; breaks branches off trees; pushes
over shallow-rooted trees; damages sign boards
F1
Moderate Tornado
73-112 mph
The lower limit is the beginning of hurricane wind speed; peels
surface off roofs; mobile homes pushed off foundations or
overturned; moving autos pushed off the roads; attached garages
may be destroyed.
F2
Significant Tornado
113-157 mph
Considerable damage. Roofs torn off frame houses; mobile homes
demolished; boxcars pushed over; large trees snapped or
uprooted; light object missiles generated.
F3
Severe Tornado
158-206 mph
Roof and some walls torn off well constructed houses; trains
overturned; most trees in fores uprooted
F4
Devastating Tornado
207-260 mph
Well-constructed houses leveled; structures with weak
foundations blown off some distance; cars thrown and large
missiles generated.
F5
Incredible Tornado
261-318 mph
Strong frame houses lifted off foundations and carried
considerable distances to disintegrate; automobile sized missiles
fly through the air in excess of 100 meters; trees debarked; steel
re-inforced concrete structures badly damaged.
F6
Inconceivable
Tornado
319-379 mph
These winds are very unlikely. The small area of damage they
might produce would probably not be recognizable along with the
mess produced by F4 and F5 wind that would surround the F6
winds. Missiles, such as cars and refrigerators would do serious
secondary damage that could not be directly identified as F6
damage. If this level is ever achieved, evidence for it might only be
found in some manner of ground swirl pattern, for it may never be
identifiable through engineering studies.
Hurricane
• A large, swirling, low pressure system that
forms over the warm Atlantic ocean. (pg. 474)
• Turns heat energy into wind
• Most powerful storm
•
http://www.usatoday.com/weather/storms/hurricane/ghurricane_scale/flash.htm
CATEGORY ONE
The Saffir-Simpson Hurricane Scale
Winds 74-95 mph (64-82 kt or 119-153 kph). Storm surge generally 4-5 ft above normal. No real damage to building structures. Damage primarily to
unanchored mobile homes, shrubbery, and trees. Some damage to poorly constructed signs. Also, some coastal road flooding and minor pier damage.
Hurricanes Allison of 1995 and Danny of 1997 were Category One hurricanes at peak intensity. .
CATEGORY TWO
Winds 96-110 mph (83-95 kt or 154-177 kph). Storm surge generally 6-8 feet above normal. Some roofing material, door, and window damage of
buildings. Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed
signs, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of the hurricane center. Small craft in unprotected anchorages
break moorings. Hurricane Bonnie of 1998 was a Category Two hurricane when it hit the North Carolina coast, while Hurricane Georges of 1998
was a Category Two Hurricane when it hit the Florida Keys and the Mississippi Gulf Coast.
CATEGORY THREE
Winds 111-130 mph (96-113 kt or 178-209 kph). Storm surge generally 9-12 ft above normal. Some structural damage to small residences and utility
buildings with a minor amount of curtainwall failures. Damage to shrubbery and trees with foliage blown off trees and large tress blown down.
Mobile homes and poorly constructed signs are destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the hurricane
center. Flooding near the coast destroys smaller structures with larger structures damaged by battering of floating debris. Terrain continuously lower
than 5 ft above mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying residences with several blocks of the
shoreline may be required. Hurricanes Roxanne of 1995 and Fran of 1996 were Category Three hurricanes at landfall on the Yucatan Peninsula of
Mexico and in North Carolina, respectively.
CATEGORY FOUR
Winds 131-155 mph (114-135 kt or 210-249 kph). Storm surge generally 13-18 ft above normal. More extensive curtainwall failures with some
complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive
damage to doors and windows. Low-lying escape routes may be cut by rising water 3-5 hours before arrival of the hurricane center. Major damage to
lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as
far inland as 6 miles (10 km). Hurricane Luis of 1995 was a Category Four hurricane while moving over the Leeward Islands. Hurricanes Felix and
Opal of 1995 also reached Catgeory Four status at peak intensity.
CATEGORY FIVE
Winds greater than 155 mph (135 kt or 249 kph). Storm surge generally greater than 18 ft above normal. Complete roof failure on many residences
and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down.
Complete destructon of mobile homes. Severe and extensive window and door damage. Low-lying escape routes are cut by rising water 3-5 hours
before arrival of the hurricane center. Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of
the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the shoreline may be required. Hurricane Mitch
of 1998 was a Category Five hurricane at peak intensity over the western Caribbean. Hurricane Gilbert of 1988 was a Category Five hurricane at
peak intensity and is the strongest Atlantic tropical cyclone of record.
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Continental Deflection
Global Forces Transparency
Equator
Earth’s Rotation
Continental Deflection
Since the Earth’s
surface is not fully
covered by water,
currents cannot
move freely around
the world. So when
surface currents
meet continents,
they deflect, or
change direction.
2
1
3
Predict what will happen with each labeled area.
Continental Deflection
Global Forces Transparency
Coriolis Effect
Equator
Earth’s Rotation
Coriolis Effect
The Earth’s
rotation
causes
surface
currents to
move in
curved paths
rather than in
a straight
line.
North
Pole
Earth’s Rotation
Global Winds
Continental Deflection
Global Forces Transparency
Coriolis Effect
Equator
Earth’s Rotation
Global Winds
Global winds are
affected by their
latitude and the
Coriolis Effect. In the
tropics winds blow
from the east to the
west. In more
temperate areas, the
winds blow from the
west to the east. Near
the poles the winds
blow from the east to
the west.
Polar Easterlies
Westerlies
Tradewinds
Tradewinds
Westerlies
Polar Easterlies
Global Winds
Continental Deflection
Global Forces Transparency
Coriolis Effect
Deep Ocean
Currents
Equator
Earth’s Rotation
Deep Ocean Currents
• Deep cold currents
move water toward
the equator.
• Cold water rises to
replace warm water
leaving.
• Warm water travels
near the surface
toward polar regions.
• Warm water replaces
cold water.
Continental Deflection
Since the Earth’s surface is
not fully covered by water,
currents cannot move freely
around the world. So when
surface currents meet
continents, they deflect, or
change
direction.
Global Forces Transparency
Global Winds
Global winds are affected
by their latitude and the
Coriolis Effect. In the
tropics winds blow from
the east to the west. In
more temperate areas,
the winds blow from the
west to the east. Near
the poles the winds blow
from the east to the west.
Coriolis Effect
The Earth’s
rotation causes
surface currents to
move in curved
paths rather than
in a straight line.
Equator
Earth’s Rotation
Deep Ocean
Currents
Deep cold currents
move water toward the
equator.
Cold water rises to
replace warm water
leaving.
Warm water travels
near the surface
toward polar regions.
Warm water replaces
cold water.