OVERVIEW

This chapter explores climates that are found poleward of the tropics of cancer and capricorn.

• Midlatitude and high-latitude climates as a group:
  • occupy the midlatitude zone, part of the subtropical zone and extend poleward into the subarctic latitude zone.
  • are located mainly in the northern hemisphere.
  • are affected by the poleward portion of the subtropical high-pressure cells, the westerly wind belt and the conflict between warm and cold air masses that occurs along the polar front zone.
• The dry subtropical climate:
  • is a poleward extension of the dry tropical climate, but shows a greater annual temperature range due to its higher latitude.
  • experiences a cool or cold season influenced by invasions of air from higher latitudes.
  • receives occasional precipitation from midlatitude cyclones.
  • is divided into arid and semi-arid subtypes.
  • has more abundant vegetation than the dry tropical climate due to lower temperatures and slightly more precipitation.
  • supports plants and animals that have adapted their life cycles to take advantage of infrequent periods of rain
  • supports agriculture only under irrigation.
• The moist subtropical climate:
  • is created by warm, moist air flowing out of the subtropical high presure cells onto the eastern sides of the continents.
  • has abundant summer rainfall, mainly convectional with an occasional tropical cyclone.
  • in Southeast Asia experiences a strong monsoon effect.
  • receives winter precipitation from wave cyclones while the storm tracks are in their most southerly position.
  • abundant yearly precipitation provides ample water for urban and industrial development but may cause flooding.
  • supports broadleaf deciduous and evergreen forests and some needleleaf and pine forests
  • soils are depleted by high rainfall as nutrients are washed out of the soil.
• The Mediterranean climate:
  • experiences a very dry summer due to migration of the subtropical high-pressure cell into the area.
  • winter is dominated by rainfall provided by cP air masses and cyclonic storms.
  • has a moderate temperature range.
  • is limited to narrow coastal zones.
  • is a pleasant climate for humans although there are problems with water availability in summer and plants must adapt to the dry summer period.
• The marine west coast climate:
  • experiences mild temperatures with a small temperature range for its latitude.
  • is a moist climate with a winter precipitation maximum due to frequent cyclonic storms. In summer the northward movement of the subtropical high pressure cell reduces precipitation.
  • supports needleleaf forests in the wet mountainous areas of Pacific North America and deciduous trees in the relatively drier areas in Europe.
• The dry midlatitude climate:
  • influences the interior regions of North America and Eurasia.
  • in some areas, the rainshadow effect blocks maritime air masses so drier continental air masses dominate.
  • summer rainfall is largely convectional associated with occasional maritime air masses.
  • has a strong annual temperature range with warm to hot summers and cold to very cold winters.
  • includes arid and semi-arid environments ranging from cold desert to steppes.
  • soils have a high natural fertility and support a vegetation of short grass prairie with moisture the limiting factor.
  • experienced serious land degradation during the drought years of the 1930's after vast areas of land in this climate type were broken for agriculture.
• The moist continental climate:
  • is found in central and eastern North America and Eurasia.
  • exhibits large seasonal temperature variation as well as strong day-to-day variation.
  • receives ample precipitation peaking in the summer with mT air masses while the winter is dominated by cP and cA air masses.
  • in East Asia experiences a monsoon effect which increases summer precipitation.
  • supports a native vegetation of deciduous forest which grades into tall grass prairie toward continental interiors.
  • soils show some leaching and acidity due to an abundance of precipitation
  • supports large scale agriculture.
• The high latitude climates:
  • are located in the westerly wind belt.
  • are influenced by mP air masses conflicting with cP and cA air masses and wave cyclones which develop along the arctic-front zone.
  • experience higher summer precipitation brought in by mT air masses.

The boreal forest climate:

• has long, bitterly cold winters and short cool summers.
• experiences a very large annual temperature range as a result of its continental location.
• is a source region for cP air masses and invasions of cA air masses are common.
• has low total annual precipitation with a summer precipitation maximum produced by maritime air masses.
• supports a native vegetation of needleleaf trees which supply the pulpwood and lumber industry. Agriculture is practised along milder coastal areas.

• The tundra climate:
  • is found along arctic coastal areas.
  • experiences long severe winters dominated by cP, mP, and cA air masses.
  • has a smaller temperature range than expected for its latitude due to the moderating effect of the nearby ocean.
  • vegetation consists of grasses, sedges, lichens and some shrubs. Species diversity is low but the number of individuals is high.
  • soils are poorly developed and are underlain with permafrost.
• Permafrost is permanently frozen ground overlain by an active layer that thaws during the summer.
• The tundra climate is cold enough to create continuous permafrost, frozen ground with few gaps or interruptions. Discontinuous permafrost occurs in patches and is found in the boreal forest climate.
• The ice sheet climate:
  • is the source region of arctic and antarctic air masses.
  • occurs on the ice sheets of Greenland and Antarctica and over the Arctic ocean ice.
  • experiences the lowest mean annual temperature, no month has a mean temperature above freezing.
  • has very low precipitation which doesn't completely melt away because the air is too cold.
  • is a very harsh environment, devoid of soils and vegetation and the few species of animals found in this climate are marine oriented.

KEY TERMS

midlatitude        moist continental  alpine tundra      
climates           climate            tree line          
dry subtropical    broadleaf          active layer       
climate            evergreen forest   continuous         
moist subtropical  tall grass         permafrost         
climate            prairie            discontinuous      
Mediterranean      high-latitude      permafrost         
climate            climates           thermal erosion    
sclerophylls       boreal forest      ice sheet climate  
marine west coast  climate                               
climate            tundra climate                        
dry midlatitude                                          
climate                                                  

STUDY QUESTIONS

1. Why are the climates in the midlatitude zone so variable?
2. What climatic factors shape the dry sutropical climate?
3. How have species adapted to the climate of the subtropical desert?
4. What role does the subtropical high-pressure cell play in the moist subtropical climate?
5. Why is the Mediterranean climate stressful for vegetation? How does the vegetation adapt?
6. What climatic factors determine the marine west coast climate?
7. What is the steppe subtype of the dry midlatitude climate so important for agriculture?
8. What air masses influence the moist continental climate?
9. Why does the boreal forest climate have the largest annual temperature range of the climates?
10. How are the boreal forest and tundra climates similar? How are they different?
11. What is permafrost? Where does it occur? Why are permafrost environments fragile?