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 Transferred1. 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/crls.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.

El Nino Conditions

Normal 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.

• The state of the atmosphere at a specific time and place.

Weather

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

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The Saffir-Simpson Hurricane Scale

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CATEGORY ONE 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.

Equator

Earth’s Rotation

Continental Deflection

Global Forces Transparency

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.

Equator

Earth’s Rotation

Continental Deflection

Coriolis Effect

Global Forces Transparency

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

Equator

Earth’s Rotation

Continental Deflection

Coriolis Effect

Global Forces TransparencyGlobal Winds

Global WindsGlobal 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.

Tradewinds

Tradewinds

Westerlies

Westerlies

Polar Easterlies

Polar Easterlies

Equator

Earth’s Rotation

Continental Deflection

Coriolis Effect

Global Forces TransparencyGlobal Winds

Deep Ocean Currents

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.

Equator

Earth’s Rotation

Continental DeflectionSince 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 changedirection.

Coriolis EffectThe Earth’s rotation causes surface currents to move in curved paths rather than in a straight line.

Global Forces TransparencyGlobal 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.

Deep Ocean CurrentsDeep 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.