Earth’s Climates

Review of last lecture1.1. The developmental stages and vertical structure of The developmental stages and vertical structure of

middle latitude cyclones (boundary between middle latitude cyclones (boundary between northern cold air and southern warm air, upper level northern cold air and southern warm air, upper level low to the west of surface low)low to the west of surface low)

2.2. How upper level longwaves and shortwaves may How upper level longwaves and shortwaves may enhance cyclonic development at the surface (upper enhance cyclonic development at the surface (upper level low to the west of surface low)level low to the west of surface low)

3.3. The three regions of cyclogenesis and typical tracksThe three regions of cyclogenesis and typical tracks4.4. Lake effectLake effect5.5. Anticyclones, heat waves and droughtsAnticyclones, heat waves and droughts6.6. Climate change: Climate change: move the tracks of the midlatitude

cyclones towards the poles

Climate and Controlling Factors

• Climate is the long-term statistical properties of the atmosphere for an area.

• Climate analysis for an area includes many variables.

• Climate classifications are based on properties such as temperature, precipitation, air mass types, and seasonal variations in water balance for an area.

The Koeppen System

• The Koeppen climate classification system is based on natural vegetation types as indicators of average temperature and precipitation.

• divides climates into five main groups, each having several types and subtypes.

• Each particular climate type is represented by a 2 to 4 letter symbol

The Koeppen System: 5 main groups• A — Tropical. Climates in which the average temperature

for all months is greater than 18°C (64°F). Almost entirely confined to the region between the equator and the tropics of Cancer and Capricorn.

• B — Dry. Potential evaporation exceeds precipitation.• C — Mild Midlatitude. The coldest month of the year has

an average temperature higher than –3°C (27°F) but below 18°C (64°F). Summers can be hot.

• D — Severe Midlatitude. Winters have at least occasional snow cover, with the coldest month having a mean temperature below –3°C (27°F). Summers are typically mild.

• E — Polar. All months have mean temperatures below 10°C (50°F).

The Koeppen System: 5 main groups

The Koeppen System: Subgroups

Video: From pole to pole

Tropical Climates

• Warm annual temperatures and with little temperature variation.• Distinguished by precipitation variations.

Tropical Wet (Af) (rainforest)

Even precipitation

Tropical Monsoonal (Am)

significant change of precipitation

Tropical Wet and Dry (Aw)

(Savanna)

Boundary with dry climate

Dry Climates• Dry climates occur in areas where potential

evapotranspiration is greater than precipitation.

• 30% of Earth’s land surface is classified as a dry climate.

• Semideserts are transitional zones that separate the true deserts from adjacent climates.

• They are also called steppe climates, with reference to the associated vegetation type consisting of short grasses.

• The two-tiered system of categorization yields four types of dry climates: subtropical desert, subtropical steppe, midlatitude desert, and midlatitude steppe.

Subtropical Deserts (BWh)

Largest deserts with atmospheric subsidence and high pressure.

Subtropical Steppe (BSh) High precipitation and temperature variability.

Midlatitude Deserts (BWk)

Higher humidity and precipitation than subtropical deserts

Midlatitude Steppe (BSk) Higher annual average precipitation than deserts

Mild Midlatitude Climates• The mild midlatitude climates are located in parts of the

latitude range between 30° and 60° in either hemisphere.

• Varying precipitation systems with mild winter temperatures. Summer temperatures may be high.

• This climate group is subdivided into three climates. The mediterranean, humid subtropical, and the marine west coast climates.

Mediterranean (Csa, Csb) Distinct dry summer due to subtropical high, mild winter

Humid Subtropical (Cfa, Cwa) Eastern continental areas. Long hot and muggy summers

Marine West Coast (Cfb, Cfc) Cold ocean current mild summers and winters. Fogs, low clouds, drizzles

Severe Midlatitude Climates

• Very cold winters.• Large continental areas.• Evenly distributed annual precipitation.

Subarctic (Dfc, Dfd, Dwc, Dwd) boreal forest . Warm, short summers and extremely cold winters

Humid Continental (Dfa, Dfb, Dwa, Dwb) Eastern continents of 40°N–55°N. Abundant annual precipitation.

Polar Climates

• Very high latitudes.• Very cold.

Tundra (ET) Permafrost (permanently frozen layer below the surface)

Ice Cap (EF)

Constant ice cover. Greenland and Antarctica.

Highland Climates (H)

• Governed solely by topography, not geographic location. • Vertical zonation

Summary: The Koeppen System

• A—Tropical. Climates in which the average temperature for all months is greater than 18°C (64°F). Almost entirely confined to the region between the equator and the tropics of Cancer and Capricorn.

• B—Dry. Potential evaporation exceeds precipitation.• C—Mild Midlatitude. The coldest month of the year has an

average temperature higher than –3°C (27°F) but below 18°C (64°F). Summers can be hot.

• D—Severe Midlatitude. Winters have at least occasional snow cover, with the coldest month having a mean temperature below –3°C (27°F). Summers are typically mild.

• E—Polar. All months have mean temperatures below 10°C (50°F).