Chapter 12 Section 7 What are air masses? Objective: Describe different kinds of air masses.

Key Terms air mass: large volume of air with about the same temperature and amount of moisture throughout polar air mass: air mass that forms over cold regions tropical air mass: air mass that forms over warm regions

Air Masses Air masses form when air stays over an area for a while or moves slowly over an area more than 1,000 km across. It is affected by the region it covers Air masses that form over land are dry. Air masses that form over water are moist. Air masses that form over warm regions are warm. Air masses that form over cold regions are cold.

INFER: What is an air mass formed over the ocean in a cold region like?

Polar air masses Two kinds of polar air masses: Continental polar air masses Forms over land The United States is affected by continental polar air masses that form over Canada. Maritime polar air masses Form over oceans in cold regions, moist The United States is affected by maritime polar air masses that form over the northern Pacific and Atlantic oceans.

2. NAME: What is a cold, dry air mass called?

Tropical Air Masses Two kinds of tropical air masses: Maritime tropical air masses Form over water, moist and warm The United States is affected by maritime tropical air masses that form over the oceans, the Caribbean Sea, and the Gulf of Mexico. Continental tropical air masses Form over tropical land areas such as northern Mexico Warm and dry

3. NAME: Where do warm, moist air masses in the United States form?

12-7 Classwork What is an air mass? What is a warm, dry air mass called? Does a continental polar air mass form over land or water? What are the four kinds of air masses? What is a cold, moist air mass called?