Factors Controlling Climate
• Climate – average weather of a region
Factors Controlling Climate
• Daily & annual cycles
– Daily rotation of the Earth (day/night)
– Annual revolution around the sun (seasons)
• Longer-term cycles:
– El Nino – several years
– Continental Glaciation – hundreds of
thousands of years
• Factors influencing annual cycle of air
temp:
Factors Controlling Climate
• Factors influencing annual cycle of air
temperature:
– Latitude
– Altitude
– Coastal vs. Continental location
• Factors influencing precipitation:
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The three above, plus:
Annual & daily air temperaturess
Prevailing air masses
Relation to mountain barriers
Position of persistent low & high pressure center
Prevailing winds & ocean currents
Temperature Regimes
• Temp Regime – Annual
cycle of temp driven by
latitude & location
• Insolation is main control
on temperature
– Variation in insolation due to
latitude
• Effect of marine or
continental location
moderates variation
Precipitation Regimes
• Seven global precipitation
regions:
• 1. Wet Equatorial Belt - >2000
mm (80 in) rainfall
– mE air masses – heavy
convective rainfall
• 2. Trade-wind Coasts – 15002000 mm precip
– Narrow belts from Equator to 30°
N & S on east coast of continents
– mT air masses carried on trade
winds bring rainfall
• 3. Tropical Deserts - < 250 mm
rainfall
– Located on or near tropics
– cT air masses under subtropical
highs
Precipitation Regimes
• 4. Midlatitude deserts &
steppes – 100-500 mm
precip
– In centers of continents,
30-50°N
– In rainshadow of
mountain chains to west
• 5. Moist Subtropical –
1000-1500 mm precip
– 25-40° N & S on moist,
western side of
subtropical high
– mT air masses from ocean
provide moisture for
precip
• 6. Midlatitude West
Coast – 15002000+mm precip
– On west coasts of
continents in path of
moist westerlies
– mP air masses &
orographic
precipitation
• 7. Arctic & Polar
Deserts - <300 mm
precip
– Above 60°N & S
– cP & cA air masses
can hold little
moisture
Precipitation Regions
Isohyets – lines drawn through areas with equal annual precipitation
Seasonality of
Precipitation
• Timing of precipitation
during year key to climate
• 3 types of precipitation
patterns:
1. Uniform throughout
year
2. Precipitation maximum
during summer
3. Precipitation maximum
during winter
Climate Classification
• Based on mean monthly
values of temp & precip
• 13 climate types based
on:
– Air mass movements
– Frontal zones
• Climate types broken
into 3 groups:
– Group I – low latitudes cT, mE and mT air masses
– Group II – midlatitudes Polar front, varied air
masses
– Group III – high latitudes cP, mP and cA air masses
Climograph
• Tool for defining the
climate of a given
location or region
• Mean monthly temp on
line chart
• Mean monthly precip on
bar chart
• May include dominant
weather
systems
Low-Latitude Climates
(Group I)
• Wet Equatorial (1) –
warm to hot
w/abundant rainfall
– Example – Amazon
Basin or Congo
• Trade Wind Coastal
(2) – warm to hot
w/very rainy season
– Example – any coastal
region exposed to
trade winds
Low-Latitude
Climates (Group I)
• Wet-Dry Tropical (3) – warm to hot w/distinct wet & dry seasons
– Example – Sahel or monsoon region of central India
• Dry Tropical (4) – very hot in high-sun season, cooler in low sun
– Little to no rainfall
– Examples – Sahara Desert, Central Australia
Midlatitude Climates (Group II)
• Dry Subtropical (5) –
not as hot as dry
tropical
– Example – Death
Valley, CA
• Moist Subtropical (6) –
hot, humid summers,
mild winters, ample rain
– Example –
Southeastern US
• Mediterranean (7) – hot,
dry summers, rainy
winters
– Examples – Southern
California,
Mediterranean Sea
Midlatitude Climates
(Group II)
• Marine West Coast (8) –
warm summers, cool,
wet winters
– Expls – Northwestern US
• Dry Midlatitude (9) –
warm to hot in summer,
cold winter, little precip
– Expl – Great Plains of
North America
• Moist Continental (10) –
warm summer, cold
winter, ample precip.
– Expl – Northeastern US
High-Latitude Climates (Group III)
• Boreal Forest (11) – short, cool
summers, long, very cold winters
– Example – Siberia, Central Alaska
• Tundra (12) – short, cool summers,
winters slightly warmer than (11)
– Example – western Alaska coast
• Ice Sheet (13) – bitter cold all year
– Examples – inland Greenland and
Antarctica