Bài tập khí hậu học chương 11

11.2 The Koeppen climatic classification• The most widely used climatic classification scheme is the Koeppen system based on world distribution of natural vegetation boundaries and the c

Chapter 11

Earth’s climates

By Vu Thanh Hang, Department of Meteorology, HUS

G304 – Physical Meteorology and Climatology

• Earth’s surface would be covered by distinct climatic zone, each having properties that set them apart from the others.

• Climatologists over the years have made numerous attempts

to establish useful climatic classification schemes

11.2 The Koeppen climatic classification

• The most widely used climatic classification scheme is the

Koeppen system based on world distribution of natural vegetation boundaries and the combinations of monthly mean temperature and precipitation associated with those boundaries

• Koeppen used a multi-tiered classification system that delineated primary climates by capital letters ranging from A through E

• These five broad categories tend to arrange themselves across Earth’s surface in response to the latitude, degree of continentality, location relative to major topographic features

• The main climate groups can be briefly described as follows:

• A-Tropical: the average temperature for all months is greater than 18oC

• B-Dry: Potential evaporation exceeds precipitation

• C-Mild midlatitude: the coldest month of the year has an average temperature higher than -3oC but below 18oC Summers can be hot

• D-Severe midlatitude: winters have at least occasional snow cover, with the coldest month having a mean temperature below -3oC Summers are typically mild

• E-Polar: all months have mean temperatures below 10oC

11.2 The Koeppen climatic classification (cont.)

Climate types according to Koeppen.

11.2 The Koeppen climatic classification (cont.)

World map of Koeppen climates.

11.3 Features of climatic types

• Tropical climates (A): consist of three groups, each of which

is warm year-round

- Tropical wet climate (Af): significant rainfall every month

- Tropical wet and dry climate (Aw): has a pronounced dry season

- Monsoonal climate (Am): relative dryness for 1 to 3 months but receives sufficient moisture that vegetation need not be adapted to seasonal drought

Tropical Wet (Af) climates have no dry period and precipitation is almost always convectional with strong solar heating of the surface triggering

brief but heavy thundershowers in the mid to late afternoon.

11.3 Features of climatic types (cont.)

Monsoonal (Am) climates usually occur along tropical, coastal areas subjected to predominant onshore winds that supply warm, moist air

to the region throughout most of the year.

11.3 Features of climatic types (cont.)

Tropical Wet and Dry (Aw) often occur along the poleward margins of the Tropics and border dry climates on one side and tropical wet climates

on the other They undergo much greater seasonality in precipitation and temperature than do the tropical wet and the monsoonal climates.

11.3 Features of climatic types (cont.)

• Tropical wet and dry climates are associated with the

11.3 Features of climatic types (cont.)

• Dry Climates (B) of the world can be divided by the level of aridity and by their latitudinal position.

- Semi-deserts are transitional zones that separate thetrue deserts from adjacent climates They are also called

steppe climates, with reference to the associated vegetation

type consisting of short grasses

- True deserts are so dry that only sparse vegetationconsisting entirely of xerophytic species can take hold

11.3 Features of climatic types (cont.)

Subtropical Deserts (BWh) tend to exist in the subtropical regions, particularly within the western portions of the continents as a result

of subsidence associated with the Hadley circulation.

11.3 Features of climatic types (cont.)

Subtropical Steppe (BSh) are marked by aridity, high year-to-year

variations in precipitation, extreme summer temperatures, large annual and daily temperature ranges, and commonly border the subtropical deserts

11.3 Features of climatic types (cont.)

Mid-latitude Deserts (BWk) result from extreme continentality in regions deep within continental interiors or downwind of orographic

barriers that cut off the supply of moisture from the ocean.

11.3 Features of climatic types (cont.)

Mid-latitude Steppe (BSk) accounts for most of the arid regions of western North America and has the same temperature characteristics

as the mid-latitude deserts The primary difference between the two

is the greater amount of precipitation in the steppes

11.3 Features of climatic types (cont.)

• Mild Mid-latitude (C) climates are located in parts of thelatitude range between 30° and 60° in either hemisphere.

• The term mild refers to the winter temperatures and not

necessarily those of the summer

- Mediterranean climates can be found along the west coasts between about 25° and 40° latitude

- At about the same range of latitude on the eastern side of continents are the humid subtropical climates

- The marine west coast climates lie adjacent to and poleward of the mediterranean climates

11.3 Features of climatic types (cont.)

Mediterranean (Csa, Csb) climates are the only ones that have a distinct summer dry season and a concentration of precipitation in the winter

Annual precipitation increases with latitude and with elevation

along windward slopes in mediterranean climates.

11.3 Features of climatic types (cont.)

Humid subtropical (Cfa, Cwa) climates lie within the lower middle latitudes

of eastern North America, South America, and Asia They have a distinct tropical feel during their long summers and receive abundant precipitation.

11.3 Features of climatic types (cont.)

Marine West Coast (Cfb, Cfc) climates normally occur poleward of mediterranean climates Both summers and winters are typically mild with low annual temperature ranges and a wide range of precipitation

11.3 Features of climatic types (cont.)

• Severe Mid-latitude climate group includes two climates,

humid continental and subarctic, both of which are marked byvery cold winters

• These climates require large continental areas within the middle latitudes between about 40° and 70°

high-• Both of the severe mid-latitude climates receive precipitationthroughout the year and have no true dry season

11.3 Features of climatic types (cont.)

Humid Continental (Dfa, Dfb, Dwa, Dwb) climates are found between 40° N and 55° N in the eastern parts of continents with warm and often hot summers followed by cold winters The coniferous forest found here

is referred to as the boreal forest in North America and the taiga in Asia.

11.3 Features of climatic types (cont.)

Subarctic (Dfc, Dfd, Dwc, Dwd) climates occupy the northernmost extent

of the severe mid-latitude regions Summer temperatures are lower than humid continental regions and winter mean monthly temperatures can be extremely low Precipitation is greater in the summer than winter.

11.3 Features of climatic types (cont.)

• Polar Climates (E) exist in the highest latitudes poleward of about 70° at the high latitude boundaries of the subarctic climates.

• The most equatorward and milder of the two is the tundra At

the most poleward regions of the globe lie the true ice cap

climates

11.3 Features of climatic types (cont.)

Tundra (ET) climates are named for the associated vegetation type that consists primarily of low-growing mosses, lichens, and flowering plants,

with a few woody shrubs and trees Winters are severe with a

perennially frozen layer below the surface called permafrost.

11.3 Features of climatic types (cont.)

Polar Ice Cap (EF) areas exist where ice covers the ground the entire year The mean temperature of the warmest month does not rise above 0 °C Most areas of ice cap receive little precipitation because of the intense cold.

11.3 Features of climatic types (cont.)

• Highland Climates (H) are governed by topography and found in large mountain or plateau areas.

• This group contains an extremely rich collection of climates

• In high mountains there can be large changes in mean temperature over short distances while mountain slopes can enhance precipitation on their windward sides and simultaneously create a rainshadow downwind

11.3 Features of climatic types (cont.)