OVERVIEW

This chapter examines the way in which atmospheric circulation processes generate the phenomenon we know as weather.

• An air mass is a large body of air with a similar temperature, moisture and lapse rate characteristics over thousands of kilometers.
• The air mass characteristics are acquired in source areas where the air remains for some time allowing it to acquire the characteristics of the surface over which it rests.
• Air masses are classified on the basis of the latitude and the surface type of the source area. The main air mass classes are:
  • mT maritime tropical
  • mE maritime equatorial
  • cT continental tropical
  • mP maritime polar
  • cP continental polar
  • cA continental arctic
  • cAA continental antarctic
• A front is a boundary between one air mass and another. The leading edge of cold air advancing into an area is called a cold front. Warm air moving into an area of cold air is called a warm front.
• When a cold front overtakes a warm front and forces the warm air aloft, it is called an occluded front.
• An important weather system affecting middle and high latitudes is a traveling low pressure system called a wave cyclone. Wave cyclones move from west to east and involve interaction of warm and cold fronts that often produces cyclonic precipitation.
• A tornado is an intense low pressure system with very high wind speeds. Tornadoes develop with thunderstorms and hurricanes.
• A weather system associated with tropical areas is the easterly wave, a low pressure trough into which air converges and is lifted producing precipitation.
• A polar outbreak occurs when cold polar air forces its way into very low latitudes, bringing storms followed by cold, clear weather.
• Tropical cyclones, hurricanes and typhoons are all names for powerful storms which develop over warm ocean surfaces between 8° and 15° latitude, migrate westward and curve toward the poles.
• Tropical cyclones often create tremendous damage due to high winds, high waves, flooding and heavy rains.
• The atmospheric circulation transfers heat from equatorial regions toward the polar regions by the Hadley cell circulation, air mass movement, Rossby waves and tropical cyclones.

KEY TERMS

cyclonic          occluded front      storm surge           
precipitation     tornado             poleward heat         
wave cyclone      easterly wave       transfer              
air mass          polar outbreaks     global warming        
cold front        polar front         greenhouse gases      
warm front        tropical cyclone    storm surge           
cyclone tracks                                              

STUDY QUESTIONS

1. What two variables provide the basis for air mass classification?

2. List six kinds of typical air masses and their source regions.

3. How do cold fronts differ from warm fronts?

4. Describe the formation of a wave cyclone.

5. List the important features of a tornado.

6. How do the easterly wave and the weak equatorial low produce precipitation?

7. What is a polar outbreak?

8. Describe a tropical cyclone.

9. What type of damage is often associated with a tropical cyclone?

10. What oceanic and atmospheric processes cause heat to be transferred to the poles?

11. What questions are scientists trying to answer regarding the effect of global warming on the earth's climate?