1. Air masses can be very large in size, covering much of the land surface of a continent or a body of water. They extend high up into the troposphere.

2. Temperature and humidity levels are similar throughout the entire mass. However, an air mass does modify its temperature and its humidity level as it moves away from its point of origin.

3. Continental air masses form over continents. Humidity levels within these air masses are low. Continental air masses can develop in either polar or tropical regions.

4. Maritime air masses form over an ocean. Humidity levels within these air masses are high. Maritime air masses can develop in either polar or tropical regions.

5. Air masses border one another. Their region of separation is marked by contrasting temperature and humidity levels. The boundary separating two air masses of dissimilar temperature and humidity levels is called a front.

6. Because the atmosphere is constantly in motion, the United States can experience a variety of air masses.

Types of Air Masses and their Characteristics

Continental Polar Air (cP) 1. Continental polar air usually brings fair weather to an area. 2. A continental polar air mass can form over the land during the winter months. In the Northern Hemisphere, it originates in northern Canada or Alaska. As it moves southward, it brings dry weather conditions to the United States. Temperature and humidity levels are both low. 3. Continental polar air can also invade the United States during the summer months, bringing mild temperatures and dry air. It often provides a refreshing break from summer heat waves.

Continental Arctic Air (cA) 1. Continental arctic air forms over frozen portions of the Arctic Ocean and its surrounding coastline. Whereas continental polar air can form at any time of the year, continental arctic air is most likely to form from early December to mid-March when the Arctic Ocean is covered with ice. 2. Continental arctic air is much colder and drier than continental polar air. Temperatures associated with continental arctic air are often below zero in northern parts of the United States.

3. In the United States, continental arctic air is usually confined to areas east of the Rocky Mountains. These tall mountains generally block the cold air from moving west.

Continental Tropical Air (cT) 1. Continental tropical air is associated with hot. dry, and sunny weather .

2. Continental tropical air is most commonly found in west Texas and in other parts of the American Southwest. On occasion, this type of air can invade the Great Plains states.

3. Because it contains little moisture, continental tropical air is often responsible for drought conditions.

Maritime Polar Air (mP)

1. Most Maritime polar air masses that affect the United States are formed in the north Pacific Ocean. Occasionally, however, maritime polar air forms in the North Atlantic Ocean, and moves into the New England states.

2. Maritime polar air is not as cold as continental polar air. Temperatures generally remain above freezing within this air mass, except at higher altitudes.

3. Maritime polar air is more humid than continental polar air because it forms over the ocean.

4. Maritime polar air has its most direct effect on the West Coast of the United States during the winter months. As a consequence, West Coast residents experience winter rain showers. The winter months can be chilly in this part of the country, but it is rare for temperatures to be extremely cold .

5. Maritime polar air which invades the United States' West Coast during the summer months often creates foggy conditions.

Maritime Tropical Air ( mT) 1. Maritime tropical air forms in subtropical regions such as the Gulf of Mexico and the Caribbean Sea. It is associated with warm, humid weather and thunderstorms.

2. Maritime tropical air is most commonly found in the United States during the summer months.

3. Maritime tropical air generally affects temperature and humidity levels in the southeastern United States. However. on occasion, it can extend further 'inland, affecting weather in the northeastern, Great Lakes and southwestern regions of the United States.

EARTH SCIENCE Assignment # _____

Name:______Date:______Period:_____

Directions: 1. Fill in the data table with the correct information for each of the air masses shown on the map. 2. Place the correct SYMBOL for each air mass on the map.

Number Name Symbol Warm or Cold? Wet or Dry? 1 2 3 4 5 6 7

7

____ 7 ____

7

____