Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(1 of 16)
Further Reading: Chapter 11 of the text book
Outline
- dry and moist subtropical climate regimes
- mediterranean regimes
- marine west coast regimes
- dry mid-latitude and moist continental regimes
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(2 of 16)
Introduction
• Previously,
– We looked at low-latitude climates
– Tend to be uniformly warm
– Principally differentiated by variations in precipitation
• Today,
– We shall look at the mid-latitude climates
– As opposed to low-latitude climates these climate regimes are differentiated
by their temperature characteristics as well as their precipitation
characteristics
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(3 of 16)
Mid Latitude Climatic Regimes
– Climates located between 25N-55N (mostly in the Northern Hemisphere -> not
much land mass in these latitudes in the SH)
– Influenced by
• Pressure and wind systems
– Northern zone of subtropical high
– Polar front
• Synoptic changes in Air Masses and fronts
– mT, mP, cP
1. Dry Subtropical Regime
2. Moist Subtropical Regime
– Traveling cyclones
3. Mediterranean Regime
• Strong seasonality in insolation
• Seasonality in pressure systems
4. Marine West Coast Regime
– Land-sea temperature differences
5. Dry Mid-latitude
6. Moist Continental
– Cyclone formation and movement
– Produces 6 different climate regimes
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(4 of 16)
Dry Subtropical Climates-1
Pole-ward extension of Dry Tropical regime (25-35N) with
slightly higher seasonality in temperature and precipitation
Subtropical High
Subtropical High
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(5 of 16)
Dry Subtropical Climates-2
(Yuma, Arizona)
– Seasonality in temperature due to changes in insolation
– There is also some seasonality in precipitation due to the wintertime influence
of midlatitude cyclones
– Vegetation consists typically of drought-resistant species such as cactus
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(6 of 16)
– Eastern subtropical regions
Moist Subtropical Climates-1
– Have consistent high humidity due to mT air from the western edge of the subtropical
high
– In the summer there is also the influence of tropical cyclones
Jet Stream
H
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(7 of 16)
Moist Subtropical Climates-2
Charleston, S. Carolina
– Seasonality in temperature due to changes in insolation - typically hot summers;
winters are cooler with the occasional incursion of cP air which leads to freezes
– Precipitation due mainly to convective activity in the summer and from midlatitude
cyclones in the winter
– Vegetation is adapted to lots of water, such as mangrove swamps, etc.
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(8 of 16)
– West coast of continents (between dry subtropical and marine west coast)
Mediterranean Climates-1
– In the summer, the region is under the influence of the subtropical high -> dry, clear, warm;
influencd by mT, cT air
– In winter, the subtropical high moves south, region receives incursions of mP air, midlatitude
cyclones which brings precipitation
H
H
Jet Stream
Jet Stream
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(9 of 16)
Mediterranean Climates-2
• Temperatures are typically
mild throughout the year due to
the influence of the ocean, low
latitudes (compared with other
mid-latitude regions)
• Vegetation typically is drought
resistant, also usually fireadapted
Monterey, California
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(10 of 16)
– West coast of continents at higher latitudes
Maritime West Coast Climates-1
– Fairly persistent precipitation all year long
• In winter, region is affected by mid-latitude cyclones
• In the summer, circulation around the subtropical high results in orographic lifting as
westerlies move on shore
H
H
Jet Stream
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(11 of 16)
Maritime West Coast Climates-2
Vancouver, BC
–
–
–
–
Temperatures are typically mild throughout the year due to the influence of the ocean
Regions of high productivity
Dense forests in North America (old growth rainforests)
Agricultural centers of Europe
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(12 of 16)
Dry Mid-latitude Climates-1
– Continental interiors at mid-latitudes
– Low annual precipitation
• Westerlies flow over mountain ranges,
producing strong rainshadows
• In N. America, region stretches from
the Great Basin to the Great Plains
– Strong seasonality in temperature
• Due to changes in insolation
• Also due to influence of continental air-masses
– Winter: cold, dry air associated with cP
– Summer: hot, dry air associated with cT
cP
cT
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(13 of 16)
Dry Mid-latitude Climates-2
(Pueblo, Colorado)
– Any precipitation they do get is from passing midlatitude cyclones
– Vegetation is transitional between desert and forest -> grasslands
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(14 of 16)
– Central and eastern portions of the continents Moist Continental Climates-1
– Strong seasonality in temperature
• Due to changes in insolation
• Also due to influence of continental air-masses
– Winter: cold, dry air associated with cP
– Summer: hot, moist air associated with mT
– Typically high precipitation all year long, although variable from day to
day
• Summer: rain associated with warm, moist mT air (usually also
associated with passing fronts)
• Winter: rain associated with mid-latitude cyclones
cP
mT
H
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(15 of 16)
Moist Continental Climates-2
(Madison, WI)
– Note that precipitation decreases in the winter -> due to the fact that the
cP air has less moisture in it
– Ample water supply -> forests
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
L25: Mid Latitude Climates
Apr-23-07
(16 of 16)
Summary
• Climate dominated by several factors
– Latitude -> determines seasonality in temperature, precipitation
– Continental v. marine
• Seasonality in temperature
• Availability of moisture
– East coast v. west coast
• Interaction of the prevailing winds with land masses
• Impact of circulation around the subtropical highs
– Topography
• Creates orographic lifting, rainshadows