1. Objectives Compare and contrast weather and climate.
Section 12.1
The Causes of Weather
Objectives
Compare and contrast weather and climate.
Analyze how imbalances in the heating of Earth’s surface create weather.
Describe how air masses form.
Identify five types of air masses.

2. Section 12.1
The Causes of Weather
Air masses have different temperatures and amounts of moisture because of the uneven heating of Earth’s surface.
Review Vocabulary
heat: transfer of thermal energy from a warmer material to a cooler material

3. New Vocabulary The Causes of Weather weather air mass climate
Section 12.1
The Causes of Weather
New Vocabulary
weather
climate
air mass
source region

4. Section 12.1
The Causes of Weather
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.

5. What is meteorology? Weather versus climate
Section 12.1
The Causes of Weather
What is meteorology?
Weather versus climate
Short-term variations in atmospheric phenomena that interact and affect the environment and life on Earth are called weather.
Climate is the long-term average of variations in weather for a particular area.

6. Heating Earth’s Surface
Section 12.1
The Causes of Weather
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 relative to the plane of Earth’s orbit.

7. Heating Earth’s Surface
Section 12.1
The Causes of Weather
Heating Earth’s Surface
Imbalanced heating-due to Earth’s tilt.
Solar radiation is unequal partly due to the changing angle of incidence of the sunlight. The greater the area covered by solar radiation, the smaller the amount of heat per unit of area.

8. Heating Earth’s Surface
Section 12.1
The Causes of Weather
Heating Earth’s Surface
Thermal energy redistribution
The constant movement of air and water 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.

9. Section 12.1
The Causes of Weather
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.

10. Air Masses Types of air masses
Section 12.1
The Causes of Weather
Air Masses
Types of air masses
1.The origins of maritime tropical air are tropical bodies of water. mT
2.The southwestern United States and Mexico are the source regions of continental tropical air, which is hot and dry, especially in summer. cT

11. Air Masses Types of air masses
Section 12.1
The Causes of Weather
Air Masses
Types of air masses
3.Maritime polar air masses form over the cold waters of the North Atlantic and North Pacific. mP
4.Continental polar air masses form over the interior of Canada and Alaska, and carry frigid air southward in the winter. cP

12. Air Masses Types of air masses
Section 12.1
The Causes of Weather
Air Masses
Types of air masses
5.Earth’s ice- and snow-covered surfaces above 60 N latitude in Siberia and the Arctic Basin are the source regions of Continental arctic air masses. cA

13. Air Masses Air mass modification
Section 12.1
The Causes of Weather
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.

14. Air Masses Air mass modification
Section 12.1
The Causes of Weather
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.

15. 12 Meteorology Climate is the long-term average of weather. a. true
12.1 Section Questions
Climate is the long-term average of weather.
a. true
b. false

16. 12
Meteorology
12.1 Section Questions
Which type of air mass forms over the North Pacific Ocean?
a. arctic
b. continental polar
c. maritime polar
d. maritime tropical

17. 12
Meteorology
12.1 Section Questions
Why does Earth’s equator receive more solar energy than Earth’s poles?

18. 12
Meteorology
12.1 Section Questions
Answer: Sunlight strikes Earth’s equator at a high angle throughout the entire year. Sunlight strikes Earth’s poles at a low angle throughout the entire year. The high-angle rays that strike the equator provide more energy per unit of surface area than the low-angle rays that strike the poles.