1. Essential Questions
What is the difference between weather and climate?
How do imbalances in the heating of Earth’s surface create weather?
How do air masses form?
What are the five types of air masses?
The Causes of Weather
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2. Vocabulary Review New heat weather climate air mass source region
The Causes of Weather
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3. What is meteorology?
Meteorology is the study of atmospheric phenomena.
The root word of meteorology is the Greek word meteoros, which means high in the air.
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The Causes of Weather

4. What is meteorology? Weather versus climate
Short-term variations in atmospheric phenomena are called weather.
Climate is the long-term average of variations in weather for a particular area.
The Causes of Weather
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5. Heating Earth’s Surface Imbalanced heating
One reason that temperatures may vary from location to location at a certain time of year is that Earth’s axis of rotation is tilted in relation to of Earth’s orbit.
Solar radiation is unequal partly due to the changing angle of incidence of the sunlight.
The Causes of Weather
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6. Heating Earth’s Surface
Thermal energy redistribution
The constant movement of air redistributes thermal energy around the world.
Weather—from thunderstorms to large-scale weather systems—is part of the constant redistribution of Earth’s thermal energy.
The Causes of Weather
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7. Air Masses Types of air masses
An air mass is a large volume of air that has the same characteristics, such as humidity and temperature, as its source region.
A source region is the area over which an air mass forms.
Types of air masses
The origins of maritime tropical air are tropical bodies of water.
The southwestern United States and Mexico are the source regions of continental tropical air, which is hot and dry, especially in summer.
The Causes of Weather
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8. Air Masses Types of air masses
Maritime polar air masses form over the cold waters of the North Atlantic and North Pacific.
Continental polar air masses form over the interior of Canada and Alaska, and carry frigid air southward in the winter.
Earth’s ice- and snow-covered surfaces above 60° N latitude in Siberia and the Arctic Basin are the source regions of arctic air masses.
The Causes of Weather
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9. Air Masses Air mass modification
When an air mass travels over land or water that has characteristics different from those of its source region, the air mass can acquire some of the characteristics of that land or water and undergo modification.
The Causes of Weather
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10. Air Masses Air mass modification
As the cold, continental polar air moves over the warmer Great Lakes, the air gains thermal energy and moisture. This modified air cools as it is uplifted and produces lake-effect snows.
The Causes of Weather
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11. Review Essential Questions Vocabulary
What is the difference between weather and climate?
How do imbalances in the heating of Earth’s surface create weather?
How do air masses form?
What are the five types of air masses?
Vocabulary
weather
climate
air mass
source region
The Causes of Weather
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