OVERVIEW

This chapter brings together many of the ideas of the previous chapters and introduces you to the processes and factors that produce different climates on the earth. Individual climates are further discussed in chapters 8 and 9.

• The climate of an area refers to the average weather conditions over a long period of time based on measurements of temperature and precipitation.
• Important principles to help you understand climate are:
  • Low-latitude locations have warmer temperatures and smaller annual temperature ranges than high-latitude locations.
  • Continental locations tend to have much larger annual temperature ranges than coastal locations at the same latitude.
  • Colder locations tend to have less precipitation than warm locations because warm air can hold more moisture than cold air.
  • The basic control on temperature is latitude, while the effect of a continental or maritime location is an important secondary control.
• Some generalizations about precipitation are:
  • Pressure systems and the global circulation are the major determinants of precipitation patterns.
  • The equatorial region experiences high convectional precipitation because of heating. These areas of high precipitation extend north and south along the east sides of the continents because the trade winds bring moisture onto the land.
  • The subtropical high pressure cells, characterized by dry, subsiding air, produce arid and semiarid regions.
  • Mountain ranges produce wet areas where air masses are forced to rise over the mountains creating an orographic effect.
  • Coastal mountains also act as barriers to moisture producing a rainshadow effect on the left side of the mountains.
  • Continental interiors tend to be dry because they are far away from the source areas of moist air masses.
• Three types of yearly precipitation patterns are:
  • Uniformly distributed precipitation.
  • Precipitation maximum during the warmest period of the year.
  • Precipitation maximum during the coolest period of the year.
• Seven global precipitation regions can be identified on the basis of these principles:
  • Wet equatorial
  • Trade wind coasts
  • Tropical Deserts
  • Midlatitude deserts and steppes
  • Moist subtropical
  • Midlatitude west coasts
  • Arctic and Polar Deserts
• Low-latitude climates are dominated by cT, mT and mE air masses. The position of the ITC and the subtropical high-pressure cells affect these climates throughout the year. Weather disturbances include the easterly wave and tropical cyclones. This group of climates includes:
  • Wet equatorial
  • Monsoon and trade-wind coast
  • Wet-dry tropical
  • Dry tropical
• Midlatitude climates occupy the polar front zone where warm and cold air masses conflict producing wave cyclones. This groups of climates includes:
  • Dry subtropical
  • Moist subtropical
  • Mediterranean
  • Marine west-coast
  • Dry midlatitude
  • Moist continental
• High latitude climates are dominated by polar and arctic air masses. They are sources areas of cP, mP cA and cAA air masses. Continental polar air meets cA air along the arctic front zone. This group of climates includes:
  • Boreal forest
  • Tundra
  • Ice Sheet

KEY TERMS

time cycles        dry subtropical    intertropical      
isohyets           moist subtropical  convergence zone   
climate            mediterranean      subtropical        
climograph         marine west-coast  high-pressure      
wet equatorial     dry midlatitude    cell               
monsoon and        moist continental  fronts             
trade-wind coast   boreal forest      air masses         
wet-dry tropical   tundra             rainshadow         
dry tropical       ice Sheet          adiabatic          
                                      cyclonic activity  
                                      steppes            

STUDY QUESTIONS

1. How does climate differ from weather?
2. How do latitude and location affect temperature regimes?
3. What factors influence precipitation patterns?
4. List the 7 precipitation regions. What are the major factors influencing precipitation patterns in each of these regions.
5. List the 3 seasonal precipitation patterns and explain why they occur.
6. What variables are the climate classifications in the text based on?
7. List the 13 climates discussed in your text. Group them into Low- latitude, Midlatitude and High-latitude climates. Summarize the main points of each climate in a sentence or two.