Journal #44 How often do you watch the weather on TV/internet? Why? What kinds of weather or weather conditions are there? Can you name situations in which weather has impacted your life or affected your plans? Explain. What kinds of elements, things, or conditions influence the weather? Why is the study of weather important? Offer examples. Why do people in general pay little attention to the weather? Do you think this is a good idea? Why or why not?

Today, we will explain how an air mass forms.

Air Masses Differences in air pressure Wind patterns Video What causes these differences? Wind patterns Caused by differences in air pressure. Video Characteristics of Air Masses

How Air Moves Air moves from high pressure to areas of low pressure. Surface air from the poles moves toward the equator. At high altitudes, warm air from the equator moves toward the poles. Temperature and pressure differences create 3 wind belts in the Northern hemisphere and 3 in the southern.

The Coriolis Effect The Coriolis effect occurs when winds are deflected by Earth’s rotation. The Coriolis effect also influences wind patterns. The processes that affect air movement also influence storms.

Formation of Air Masses When air pressure differences are small, air remains stationary (in place) or moves slowly. If the air remains stationary, the air takes on characteristic temperatures and humidity of that region. A large body of air throughout which temperature and moisture are similar is called an air mass. What are air masses like over polar regions? What about air masses over tropical regions

Types of Air masses Air masses are classified according to their source regions. Temperature Humidy The source regions for warm air masses are tropical areas The source regions for cool air masses are polar areas. Air masses that form over oceans are called maritime. Air masses that form over land are called continental.

Types of Air Masses (cont) Maritime air masses are moist and continental air masses are dry. Air masses symbols: Continental- c Maritime- m Tropical- T Polar-P Combinations of air results in air masses with distinct characteristics.

Continental Air Masses These air masses form over large landmasses (northern Canada, northern Asia, southwestern US) Form over land so the humidity is low. The air mass will eventually move into other regions because of global wind patterns. They bring dry weather conditions

Types of Continental Air Masses There are 2 types of continental air masses: Continental polar (cP)- cold and dry Continental tropical (cT)- warm and dry

Maritime Air Masses Maritime air masses form over oceans or other large bodies of water. Humidity of these air masses tends to be higher than continental air masses When theses humid air masses travel they bring more precipitation and fog

Types of Maritime Air Masses There are 2 types of maritime air masses Maritime polar (mP)- moist and cold Maritime tropical (mT)- moist and warm

Source- Region of Air Mass Air Masses Source- Region of Air Mass Type of Air (Weather) Symbol Colored Picture: (blue=cold) (red=warm) Continental Polar Continental Tropical Maritime Tropical Maritime Polar

North American Air Masses The four types of air masses that affect the weather of North America come from 6 regions. An air mass usually brings the weather of its source region, but may change as it moves away. Example: What will happen if cold dry air moves towards warm ocean? What weather would you expect?

Your assignment: Air Masses Activity

Air Mass #1

Air Mass #1 Those who live in northern portions of the United States expect cold weather during the winter months. These conditions usually result from the invasion of cold arctic air masses that originate from the snow covered regions of northern Canada. Because of the long winter nights and strong radiational cooling found in these regions, the overlying air becomes very cold and very stable. The longer this process continues, the colder the developing air mass becomes, until changing weather patterns transport the arctic air mass southward.

Air Mass #2

Air Mass #2 Maritime Tropical Air Masses- Warm temperatures and rich in moisture Maritime tropical air masses originate over the warm waters of the tropics and Gulf of Mexico, where heat and moisture are transferred to the overlying air from the waters below. The northward movement of tropical air masses transports warm moist air into the United States, increasing the potential for precipitation.

Review: What are the characteristics of maritime tropical air masses? Where do they originate? How do they affect weather?  (The characteristics are warm temperatures, rich in moisture. They originate over the warm waters of the tropics and Gulf of Mexico. The northward movement of tropical air masses transports warm moist air into the United States, increasing the chances of precipitation.)

Review: What is a continental polar air mass? Where does it originate? How does it affect weather?  It is an air mass with cold temperatures and little moisture. It originates in snow-covered regions of northern Canada. It affects weather by turning it colder. In your own words, describe the role that air masses play in weather. 

Review: What was the most challenging part of mapping out air masses? How, if any, has this lesson affected your view of weather?