Weather Systems Essential Questions What are the similarities and differences between the three major wind systems? What are the four types of fronts? How do high and low pressure systems differ?

Vocabulary Terminology Convection – The transfer of thermal energy by the flow of a heated substance. Coriolis Effect : Polar Easterlies: Prevailing Westerlies: Trade Winds: Jet Stream: Front: Vocabulary Terminology

Global Wind Systems What would happen to the cold polar air if the Earth did not rotate on its axis? What would happen to the warm equatorial air?

Earth does rotate from East to West causing Air Masses to be distributed. Coriolis Effect – Results in fluids and objects moving in a curved path rather than a straight line. Tornado’s, and toilet water rotate clock wise north of the equator and counter clockwise south of the equator.

Three Basic Wind Systems Polar Easterlies Prevailing Westerlies Trade Winds

Polar Easterlies Wind Zone This is the area between 60 N latitude and the North Pole, and 60 S latitude and the south pole. Cold dense winds that sink. Weak winds that are deflected away from the poles.

Prevailing Westerly Winds Located between 30 N to 60 N latitude, and 30 S and 60 S latitudes. These move in a westerly direction toward the poles. Steady winds that move weather across the US and Canada.

Trade Winds Trade Winds are circulation of wind belts located between 30 N and 30 S latitude. Trade Winds sink and rotate toward the equator in and easterly direction. Once it reaches the equator, it warms, rises, moves back to 30 degree latitude, cools, sinks and starts over.

Horse Latitudes Earth’s major deserts such as the Sahara are found near the 30 Nor South latitude. Air pressure is high and surface winds are low.

Tropical Convergence Zone This zone is located at the equator where the winds from the north and south meet. The winds collide and rise causing an area of low pressure. This zone drifts north or south of the equator as the seasons change. It contains bands of clouds and thunderstorms which drops rain in the tropical rain forest.

Intertropical Convergence Zone

Concepts to remember Warmer air has higher pressure than cold air. Cold air has a higher density. Changes in air pressure causes changes in wind velocity. Wind is movement of air from and area of high pressure to and area of low pressure.

Jet Streams Jet Streams result from large temperature changes in upper level air combined with the Coriolois effect causing westerly winds. Winds speeds ( up to 400 km/h) in the jet stream can vary with air temperatures.

Jet Stream Continued Jet streams vary seasonally and are generally in areas with the largest temperature differences on a line from the equator to a pole.

Types of Jet Streams Polar Jet Streams separate the polar easterlies from the prevailing westerlies. Usually found between 40 N to 60 N, and 40 S to 60 S latitudes.

Subtropical Jet Streams Considered “minor jet streams” Subtropical Jet Streams are found where the trade winds meet between the prevailing westerlies between 20 N to 30 N and 20 S to 30 S latitudes.

Jet Streams and Weather Systems Storms form along jet streams and form large scale weather systems. Cold air is pushed toward the tropics. Warm air is pushed toward the poles. Weather systems follow the jet stream and change according to the different temperatures.

Fronts Fronts are narrow regions between two air masses with different densities. These result when Two air masses collide.

Cold Front Cold fronts result from cold dense air pushing warm air up along a steep slope. As the warm air rises, it cools and condenses to produce precipitation.

Cold fronts appear as a blue line with evenly spaced triangles that point in the direction the front is moving.

Warm Front Warm air displaces cold air, forming a gradual boundary slope. Can result in light precipitation.

Stationary Front These take place when two air masses collide but neither advances. They stall. Some precipitation may exist. They can continue to move.

Occluded Front Occluded fronts occur when they collide with a warm air mass that gets pushed up, and then collide again with another cold air mass on the opposite side of the warm air mass. Strong winds and heavy rain

Occluded Front Continued On a weather map, occluded fronts will have evenly spaced alternating purple triangles and semicircles pointing the directional movement of the front.

Occluded Front > < Warm Front Cold Front > Stationary Front

Pressure Systems Low Pressure Systems – Result from air outside the system replacing the rising air of the system. Low pressure system air rises and spins counter clockwise in the northern hemisphere. Usually results in clouds and precipitation.

Pressure Systems

High Pressure Systems Sinking air moves away from the system’s center when reaching Earth’s surface. Coriolois Effect causes the air to irculate to the right in the northern hemisphere. Usually results in fair weather.

1. Describe The Coriolis effect 2. Explain why most tropical rain forest are located near the equator. 3. Why are deserts located where they are? 4. Describe how jet streams affect air mass movements. 5. Make a T chart to compare and contrast low pressure and high pressure systems.