10 Climates of the middle latitudes

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(10)Climates of the middle latitudes
GEOG 31064 Principles of Climatology (Dr.
Scott Sheridan)
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Middle Latitude climates (C,D)

• There is a summer (at least one month above 10C)
• There is a winter (at least one month below 18C)
• Just about all areas get below freezing

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Middle latitude characteristics

• Strong seasonal variability
• Air mass variability
• Rossby waves
• The mid-latitude cyclone and fronts
• Temperature variability
• Precipitation variability depends on region

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Insolation by time of year
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Synoptic temperature control
JANUARY, Akron
JULY, Akron
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Air masses and their sources
Principal air masses that affect the middle
latitudes cP (Continental Polar) cT
(Continental Tropical) mP (Moist Polar) mT (Moist
Tropical) What makes a good source region?
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Rossby wave patterns
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Rossby wave surface connection
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The mid-latitude cyclone
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Cyclone track density
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Cyclone frequencies
Cyclogenesis
Cyclolysis
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C (Subtropical) climates

• Mean temperature of coldest month less than 18C
  (64F), but warmer than -3C (28F)
• Enough precipitation to not be B climate
• Three main subdivisions
• Csa, Csb (Mediterranean) dry summer
• Cfb, Cfc (Marine west coast) cool summer
• Cfa, Cwa (Mid-latitude rainy and winter drought)
• Mediterranean and Marine West Coast grade into
  one another physically separate from Cfa / Cwa

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Cs (Mediterranean)
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Cs thermal characteristics

• Cold weather notably absent here
• Some places rarely freeze
• Winter temperatures among mildest in middle
  latitudes
• Low annual range for mid-latitudes
• 15F to 25F range
• Subdivided by summer temperatures
• Csa warm summers (hottest month gt22C)
• Csb cool summers (hottest month lt22C)

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Cs climate characteristics

• Modest precipitation (usually 10-20)
  concentrated in winter
• Mid-latitude cyclones affect area in winter
• Only mid-lat. climate with summer drought
• Under subtropical high in summer
• Also along cold current ocean in most cases
• Warm to hot summers, mild winters
• Much sunshine during summer

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Cs climographs
SAN FRANCISCO , California, USA Csb cool
summer More poleward, or along coasts Fog
common Muted temperature range, Long seasonal lag
ATHENS , Greece (Csa) Csa warm summer Inland or
more equatorward Fog less common Larger
temperature ranges Hot, but never humid, summers
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Cfb, Cfc (Marine west coast)
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Cfb, Cfc Temp. characteristics

• Cool summers (hottest month lt22C)
• Low annual range for middle latitudes
• Especially cool summers
• Mild winters frosts happen but are uncommon
• Low daily range due to high cloud cover and ocean
  influence
• Extremes only happen when flow is reversed
  (easterly)

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Cfb, Cfc Precip. characteristics

• Wet and quite cloudy year round
• Generally too far north for subtropical highs to
  have much influence
• Droughts rare
• Precipitation totals low in most cases
• Many rain days with light rain
• Exception mountainous areas (eg Washington,
  Alaska, Chile)
• Snow uncommon

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Cfb climograph
WELLINGTON, New Zealand
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Cfa, Cwa (Mid-lat. rainy/win. drought)
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Comparing locations
Cfb, Cfc
Cfa, Cwa
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Cfa, Cwa Temp. characteristics

• Daytime temperatures warm to hot, mild winters
  similar to Csa
• Nighttime temperatures higher more humid
• Annual range varies according to continentality
• Frosts occur
• More in southeastern US and China than elsewhere

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Cfa, Cwa Precip. characteristics

• Dominated by warm ocean currents
• High annual totals, 25 to 60 inches
• Warm season precipitation convectional
• More absolute precipitation in summer more wet
  days in winter
• Summers are wet
• Cfa winters are wet
• Cwa winters are dry

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Cfa, Cwa climographs
SYDNEY, Australia Cfa wet winter Smaller
temperature range
SEOUL, S. Korea Cwa dry winter Larger
temperature range
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D (Microthermal) climates

• Dominance of continental influence
• At least one month with mean temperature below
  -3C (28F)
• Poleward of C climates
• Do not appear on west coasts or in Southern
  Hemisphere
• Large annual temperature range
• Cold winters
• Seasonal snow cover

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Types of D climates

• Da, Db warm and mild summers
• Da warmest month gt22C (71F)
• Db warmest month lt22C, but 4 months gt10C
  (50F)
• Dc, Dd cool summers and cold winters
• Both less than 4 months gt 10C
• Dd really cold winters , at least one month
  below -38C (-36F)
• Dw climates in China, Russia (dry winter)
• Df elsewhere (wet year-round)

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Da, Db (warm summers)
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Da, Db climate character

• Temperature
• Climates most susceptible to heat waves and cold
  spells
• Westerlies bring continental influence right to
  coast
• Large fluctuations in day-to-day temperatures
• Precipitation
• Moderate amounts of precipitation, 20 to 40 in.
• Precipitation totals lower poleward and away from
  mountains
• Snowcover persists on the ground part of the year

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Da climographs
BEIJING, China Dwa dry winters
CLEVELAND, Ohio, USA Dfa wet winters
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Dc, Dd (cool summers)
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Dc, Dd climate character

• Temperature
• Most extreme continental climates
• Some summer, though not a long one
• Brief springs and autumns
• Precipitation
• Low totals (generally under 20 in.), often much
  less
• Summer maximum in precipitation
• Little precipitation in winter all snow
• Generally clear skies in winter

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Dwd climograph
VERKHOYANSK, Russia Mean precipitation 5 Widest
temperature range in world Record High
99F Record Low -90F Average January High
Temperature -54F