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:– 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 – 1500-2000 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 – 1500-2000+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

• 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

Low-Latitude Climates (Group I)

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

• 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

Midlatitude Climates (Group II)

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