Introduction to Meteorology UNIT 10 STANDARDS: NCES 2.5.1, 2.5.2, 2.5.3, 2.5.4, 2.5.5, LESSON 1

Lesson Objectives In this lesson, you will learn about: What determines global weather patterns How air masses move and change Effective weather forecasts How to create a weather chart How to read a weather map

Meteorology The study of the atmospheric phenomena. Clouds and precipitation are the main areas of study.

Climate versus Weather (Review) Weather Climate The current state of the weather in a particular area. (It’s rainy in Raleigh) Long term variation in weather for a particular area. Average weather over time. The Bahamas are tropical islands.

The Causes of Weather Heat Moisture Winds Remember the sun’s rays heat the earth. More energy reaches the equator than the poles. The moisture in the air remains relative constant over the globe. The global air masses stay in motion. Weather is a perfect example of the redistribution of solar energy around the globe.

Air Masses Air Mass Large body of air that takes on the characteristics of an area over which it forms. Air masses forming over land have less moisture than those formed over the seas.

Classifying Air Masses (5 types) Classification Air masses are classified based on the location of their formation. Warm & Dry = continental tropical Cold & Dry = continental polar Warm & Humid = maritime tropical Cold & Humid = maritime polar Cold = Arctic

Sources of Air Masses Maritime Polar Continental Polar Maritime Tropical Continental Tropical Polar Form over North Pacific and affect West Coast Generally form in Alaska Form in the Caribbean Sea and Gulf of Mexico Generally form in the Southwest and Mexico Arctic Basin and Siberia

Air Masses Over the United States

Section Review What is the difference between weather and climate? What must happen to keep the poles from steadily cooling and the tropics from overheating? How has a maritime polar air mass modified the climate of Oregon?

Coriolis Effect If the Earth did not rotate and the cold air from the poles only went to the equator. Then the air masses would only circulate in each hemisphere. BUT The Earth rotates and causes a global circulation pattern. Air masses in the Northern Hemisphere circulate clockwise and counterclockwise in the Southern Hemisphere.

Global Wind Systems Doldrums Trade Winds Westerlies Easterlies Poor winds found at the equator because the circulation patterns cancel each other out. Equator to 30 o where winds circulate. Between 30 o and 60 o and circulate opposite to the trade winds.Flow to the east. 60 o to the poles. Similar in direction to the trade winds. Flow to the west.

Jet Streams Locations Definition Speed Importance Jet streams are found where the wind zones overlap. Narrow bands of fast, high-altitude westerly winds. Speeds approach 185 mph. Weather systems follow the path of major winds. The jet stream affect the intensity of weather system,s by moving air of different temperatures to from one region to another.

FRONTS Cause Definition Interactions The collision of different air masses with different temperatures and densities. A front is a narrow region separating two air masses of different densities. Interactions cause changes in weather. Four types: cold, warm, stationary, and occluded

Cold Fronts Cold dense air advances under warm air. Warm air is forced up As the warm air rises, moisture condenses. May produce rain to severe thunderstorms

Warm Fronts Warm air advances and forces cool air down. Moisture condenses at the bottom of the warm air. Precipitation down through the cold air. Precipitation occurs as the warm ground air meets the cool air above.

Stationary Front When two air masses meet and neither advances. Generally do not produce long term precipitation patterns

Occluded Fronts Fast moving cool air forced trapped warm air up as it pushes against another cold front. Clouds form above cold air and may condense and produce some precipitation.

High Pressure Systems Winds move OUT from the center of the high pressure cell. In high pressure systems, air is forced down toward the ground.

Low Pressure Systems Winds move IN to the center of the low pressure cell. In low pressure systems, air is pulled upward. The upward movement causes high speed winds and could become strong storms. Severe Storms !!

Comparison High-Low Systems

Section Review Discuss the global wind patterns How does the jet streams affect the movement of air masses? What is the Coriolis Effect? Compare high and low pressure systems.