Chapter%20Thirteen

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Chapter Thirteen

• Global Climate

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What we are going to learn?

• We are going to learn the answers to the
  following questions
• What are the factors that regulate global
  climate?
• How are climates are classified?
• What are the different types of climate?
• What are micro-, macro- and meso-climates?

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Climate

• Climate Average of the day-to-day weather over a
  long duration
• Microclimate Small climatic region near or on
  the ground
• Mesoclimate Climate of a small area of the
  earths surface
• Macroclimate Climate of a much larger area
  (state or a country)
• Global Climate Climate extending over the entire
  earth
• Two important weather elements temperature
  precipitation
• Climate Controls are
• Intensity of sunshine and its latitudinal
  variations
• Ocean currents and thermohaline circulation
  systems
• Relative distribution of land and water
• Wind intensity and direction
• Position of high- and low-pressure areas
• Mountain barriers
• Altitude

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Global Temperatures
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Global temperatures (cont.)

• Isotherms are oriented East-West (same latitude
  locations receive same amount of solar energy)
• Bending of isotherms along the coastal margins is
  partly due to the unequal heating cooling of
  land water
• Variation in temperature between summer and
  winter will be far greater over continental
  interiors than along the west coastal margins of
  continents climates of interior continental
  regions will be more extreme (higher summer temp
  and lower winter temp) than their counterparts in
  the west coast west coast climates are typically
  quite mild for their latitude
• Highest mean temperatures do not occur in the
  tropics, but rather, in the subtropical deserts
  of the Northern Hemisphere

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Global Temperatures (cont.)

• Lowest mean temperatures occur over large land
  masses at high latitudes coldest area of the
  world is the Antarctic
• Snow and ice reflect 80 of the sunlight that
  reaches the surface much of the absorbed solar
  energy is used to transform the ice and snow into
  water vapor
• Southern Hemisphere is cooler than Northern
  Hemisphere because
• Cold Antarctic
• Polar regions of the Southern Hemisphere reflect
  more incoming sunlight
• Less land area found in the tropical and
  subtropical areas

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Global Precipitation

• Global distribution of precipitation is closely
  tied to the general circulation of the atmosphere
  and to the distribution of mountain ranges high
  plateaus
• Equatorial regions are typically wet, while the
  subtropics and the polar regions are relatively
  dry
• Precipitation is most abundant where the air
  rises least abundant where it sinks
• In tropical regions, the trade winds converge
  along the ITCZ producing rising air --- heavy
  precipitation all year long near 30 deg, the
  sinking air of the subtropical highs produces a
  dry belt around the globe presence of Sahara
  Desert of North Africa in this region

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Annual global pattern of precipitation
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Global Precipitation (cont.)

• In the cold air of the polar regions there is
  little moisture --- winter storms drop light,
  powdery snow that remains on the ground for a
  long time because of the low evaporation rates
  in summer a ridge of high pressure tends to block
  storm systems that would otherwise travel into
  the area --- precipitation is low in the arctic
• Heaviest precipitation is concentrated in the
  eastern states, as moisture from the Gulf of
  Mexico moves northward cities on the plains
  receive more rainfall in summer those on the
  west coast have maximum precipitation in winter
• Cities in the midwest and East usually have
  abundant rainfall all year long

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Vertical cross section along a line running N-S
illustrating main global regions of rising and
sinking air
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Global climate (cont.)

• Hottest places on earth generally occur in the
  subtropical deserts of the Northern Hemisphere,
  where clear skies and sinking air produce clear
  skies and scorching heat
• Coldest places on earth tend to occur in the
  interior of high-latitude land masses The
  coldest areas of the Northern Hemisphere are
  found in the interior of Siberia and Greenland
  coldest area of the world is Antarctic
• Wettest places in the world are located on the
  windward side of mountains where warm, humid air
  rises upslope
• Driest places in the world are located on the
  leeward (downwind) side of mountains where air
  parcels undergo drying and compressional heating
  rain shadow

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Variations in annual precipitation for three
Northern Hemisphere cities
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Pacific Northwest, U.S.
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Effect of topography on average annual
precipitation along a line from the Pacific Ocean
through CA and western Nevada
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Key to map of precipitation records thoughout the
world

• Key

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Some precipitation records

• .

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Climatic Classification The Köppen System

• Similarity in climate (temperature and
  precipitation) in an area forms the basis for
  classification
• Köppen related distribution types of vegetation
  to climate five major climatic types designated
  by A (tropical moist Climate), B (dry climate), C
  (moist mid-latitude climates with mild winters),
  D (moist mid-latitude climates with severe
  winters) E (polar climates)
• Tropical Moist Climate (A) Monthly average temp
  above 18C no real winter season and year around
  warm temp. abundant rainfall (gt150 cm) extends
  from equator to 15-25 N or S
• Examples Amazon lowland of South America, the
  Congo River Basin of Africa, and the East Indies
  from Sumatra to New Guinea

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Major Climate Regions of the WorldKöppen System
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Type A Climatic zone (cont.)

• High temperature and abundant rainfall --- dense,
  broadleaf, evergreen forest tropical rain
  forest with vegetation abundant sunlight allows
  for the growth of tangled shrubs forming
  impenetrable jungle
• Major types are tropical wet (Af) and tropical
  monsoon (Am) and tropical wet and dry (Aw)
• Tropical wet climate seasonal temperature
  variations are lt 3 C greater variation in
  temperature between day night (diurnal, average
  high 32C average low 22C) than annual
  temperature variation
• towering cumulus clouds form every day to produce
  heavy, localized showers in the afternoon annual
  rainfall gt 150 cm (windward side can exceed 400
  cm/yr)
• high humidity cloud cover tend to keep maximum
  temp from reaching very high values

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Temperature and Precipitation data for Peru
(latitude 4S tropical wet climate, Af)
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Climate A Type (cont.)

• In Peru, monthly rainfall variations are more
  than the temperatures --- due to migrating
  position of the intertropical convergence zone
  (ITCZ) associated wind patterns
• Laterite A soil formed under tropical conditions
  where heavy rainfall leaches soluble minerals
  from the soils leaving soil hard and poor for
  growing crops
• Tropical Monsoon Climate When precipitation
  totals drop below 6 cm for perhaps one or two
  months a tropical climate with a brief dry
  period of perhaps one or two months examples
  coasts of southeast Asia, India, and in
  northeastern South America

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Climate A Type (cont.)

• Tropical wet and dry climate (Aw) Distinct dry
  season prevails annual rainfall gt100 cm, but
  monthly rainfall for more than 2 months is lt6 cm
  --- rainforests cannot survive to this drought
  giving rise to coarse savanna grass, scattered
  with low, drought-resistant deciduous trees
• Examples of Aw climate are western Central
  America, north and south of the Amazon Basin
  (South America), southcentral Asia and northern
  Australia

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Climate data for Timbo, Guinea (11N) tropical
wet-and-dry climate (Aw)
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Dry Climates (Group B)

• Dry Climate Evaporation (E) Transpiration (T)
  gt Precipitation (P)
• Subtropical deserts extend from 15-30 (often
  surrounded by mountains)
• 26 of land area falls in this group
• Major types Arid (BW 12 of the land) and
  Semi-arid (BS 14 of the land)
• Arid region is divided as follows
• a) BWh or BSh Climate is hot dry with a mean
  annual T of above 18C
• b) BWk or BSk Climate is cold (in winter) and
  dry with mean annual T lt 18C
• Examples for Arid region West coast of South
  America, Africa and over much of the interior of
  Australia
• In North America, arid climate extends from
  northern Mexico into the southern interior of the
  US
• Most of the native plants are xerophytes (capable
  of surviving prolonged periods of drought)

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Rain streamers (virga) in dry climates, as
falling rain evaporates into the drier air
beneath the cloud
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Bushes and cactus found in the arid southwestern
American deserts (BWh)
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Dry climate B (cont.)

• In low-latitude deserts (BWh),
• maximum daytime during the summer can gt50C
  (40-45C (104-113F) are more common) RH in the
  middle of the day 5-25
• minimum T can drop below 25C
• Mid-latitude deserts (BWk)
• Summer maximum temp reaches 40C (104F)
• Winters are extremely cold with minimum temp
  below -35C (-31F)
• Lie in the rain shadow of an extensive mountain
  chain (Sierra Nevada and Cascade mountains in
  North America), Himalayan mountains and Andes in
  South America
• Around the margins of the arid regions, where
  rainfall amounts are greater, the climate is
  gradually changes into semi-arid (BS)
• examples Most of the Great Plains, southern
  coastal sections of California, northern
  valleys of the Great Basin annual precipitation
  20-40 cm examples are Denver, Colorado

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Arid (BWh) Climate Phoenix, AZ (33.5N)
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Cumulus clouds in a semi-arid climate (BS) in
Western North America
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Climatic data for Denver, CO (40N) a semi-arid
climate (BSk)
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Moist subtropical mid-latitude climates (Group C)

• Humid with mild winters with the average temp of
  the coldest month -3C to 18C (27-64F)
  commonly found on the eastern and western regions
  of most continents, 25-40 latitude
• Major types Humid subtropical (Cfa), marine
  (Cfb) and dry-summer subtropical or Mediterranean
  (Cs)
• Humid subtropical climate (Cfa) Found
  principally along the east coasts of continents,
  25-40 latitude
• summer is hot and muggy summer dew-point temp
  and RH are high (exceeding 23C or 73F) Mobile,
  AL
• In winters, frost, snow, and ice storms are more
  common, but heavy snowfalls are rare
• Rainfall 80-165 cm/yr, fairly well distributed
  in an yr

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Climatic data for Mobile, Alabama (30N) a
humid subtropical climate (Cfa)
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Moist subtropical - Marine

• Marine (Cfb) Along western side of most
  continents from 40 to 60 winds from the oceans
  moderate the climate summers are quite cool
• Low annual temperature range in high latitude
  region oceans influence keeps daily temp
  ranges low
• Coastal Mediterranean Climate Precipitation
  30-90 cm/yr summer afternoon temperatures climb
  above 34C(93F) and occasionally above 40C
  (104F)
• San Francisco, CA Sacramento, CA are only 130
  km (80 miles) apart (inland) and average July
  temp is 9C (16F) higher at Sacramento

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Climatic data for Port Hardy, Canada (51N)
marine climate
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Comparison of a coastal Mediterranean climate
(Csb San Francisco) with an interior
Mediterranean climate (Csa) Sacramento
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Moist Continental Climates (Group-D)

• Warm-to-cool summers and cold winters warmest
  month average temp gt10C (50F) coldest monthly
  average temp drops below -3C (27F) D climates
  are controlled by large land masses found only
  in the Northern hemisphere D climates extend
  across North America and Eurasia (40 - 70N)
• Major types
• Humid continental with hot summers (Dfa long and
  hot summer mid-day temp exceed 32C (90F
  nights are usually warm humid),
• Humid continental with cool summers (Dfb less
  humid temp can exceed 35C (95F)) and subpolar
  (Dfe)

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Comparison of a humid continental hot summer
climate, Dfa (Des Moines) with a humid
continental cool summer climate (Winnepeg)
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Subpolar climate (Dfc) Fairbanks, AK (65N)
winters are severe, summers are short cool, 1-3
months exceed mean temp of 10C (50F)
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Polar Climate Group E

• Year-round low temp (average temp of the warmest
  month lt 10C (50 F), but above freezing
• Two major types Polar tundra (ET) and Polar ice
  caps (EF)
• Polar tundra ground is permanently frozen
  (Permafrost)
• Annual precipitation lt 20 cm (in lower latitudes,
  would constitute desert, but in the cold polar
  regions, evaporation rates are very low and
  moisture is adequate)
• Polar ice cap Temp for every month is below
  freezing, plant growth is impossible the region
  is covered with snow and ice Greenland and
  Antarctica precipitation lt 10 cm/yr

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Climate data for Barrow, Alaska (71N) polar
tundra climate (ET)
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Climatic data for Eismitte, Greenland (71N)
polar ice cap climate 3000 m above MSL (EF)
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Highland Climates (Group H)

• Varying climate with altitude 300 m elevation
  is equivalent to traveling 300 km northward (3N)
• Ascending on a mountain, one can travel through
  many climatic regions in a relatively short
  distance
• Elevation in the central Sierra Nevada
• Base of the mountain semi-arid conditions
• foothills Mediterranean and the vegetation
  changes
• higher elevations subpolar and vegetation
  changes
• near the summit, permanent patches of ice and
  snow, with some glaciers (in less than 4 km),
• the climate has changed from semi-arid to polar

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Vertical view of changing vegetation and climate
due to elevation in the central Sierra Nevada
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Chapter Summary

• Micro-, meso-, and macro-climate with examples
• Rain shadow desert and rainiest places
• Rainforests exist in what climatic conditions?
• What is a dry summer? Explain why it is a dry
  summer
• Lowest temperature and precipitation in the world
  
• Köppen classification system type A, B
• Monsoon
• Characteristics of tropical wet climate,
  wet-and-dry climate
• Most abundant climate type in the planet
• Humid Subtropical climate Mediterranean climate
  D-type climate where it is found in US
• Which climate type normally has the larges and
  smallest annual range in temp subpolar
  temperature polar ice cap climate tundra
  climate