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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) 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 La Nina The winds blowing across the Pacific are stronger than normal. El Nino Conditions 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. Cli mat e • 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. • A large, swirling, low pressure system that forms over the warm Atlantic ocean. (pg. 474) • Turns heat energy into wind • Most powerful storm Hurricanes Tornado • A violent, whirling wind that moves in a narrow path over land. Fujita Scale (Tornadoes) A large, swirling, low pressure system that forms over the warm Atlantic ocean. Turns heat energy into wind. Most powerful storm.