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Group A : Tropical Humid Climates
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- Exists between Tropic of Cancer and Tropic of Capricorn
- The sun being overhead throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ) make the climate hot and humid.
- Annual range of temperature is very low and annual rainfall is high.
The tropical group is divided into three types, namely
- Af- Tropical wet climate;
- Am – Tropical monsoon climate;
- Aw- Tropical wet and dry climate
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Tropical Wet Climate (Af)
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- Found near the equator.
- The major areas are the Amazon Basin in South America, western equatorial Africa and the islands of East Indies.
- Significant amount of rainfall occurs in every month of the year as thunder showers in the afternoon.
- The temperature is uniformly high and the annual range of temperature is negligible.
- The maximum temperature on any day is around 30°C while the minimum temperature is around 20°C.
- Tropical evergreen forests with dense canopy cover and large biodiversity are found in this climate
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Tropical Monsoon Climate (Am)
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- Tropical monsoon climate (Am) is found over the Indian sub-continent, North Eastern part of South America and Northern Australia.
- Heavy rainfall occurs mostly in summer.
- Winter is dry.
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Tropical Wet and Dry Climate (Aw)
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- Occurs north and south of Af type climate regions.
- It borders with dry climate on the western part of the continent and Cf or Cw on the eastern part.
- Extensive Aw climate is found to the north and south of the Amazon forest in Brazil and adjoining parts of Bolivia and Paraguay in South America, Sudan and south of Central Africa.
- The annual rainfall in this climate is considerably less than that in Af and Am climate types and is variable also.
- The wet season is shorter and the dry season is longer with the drought being more severe.
- Temperature is high throughout the year and diurnal ranges of temperature are the greatest in the dry season.
- Deciduous forest and tree-shredded grasslands occur in this climate.
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Dry Climates: B
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- Characterised by very low rainfall that is not adequate for the growth of plants.
- These climates cover a very large area of the planet extending over large latitudes from 15° – 60° north and south of the equator.
- At low latitudes, from 15° – 30°, they occur in the area of subtropical high where subsidence and inversion of temperature do not produce rainfall.
- On the western margin of the continents, adjoining the cold current, particularly over the west coast of South America, they extend more equator wards and occur on the coast land.
- In middle latitudes, from 35° – 60° north and south of equator, they are confined to the interior of continents where maritime-humid winds do not reach and to areas often surrounded by mountains.
- Dry climates are divided into steppe or semi-arid climate (BS) and desert climate (BW).
- They are further subdivided as subtropical steppe (BSh) and subtropical desert (BWh) at latitudes from 15° – 35° and mid-latitude steppe (BSk) and mid-latitude desert (BWk) at latitudes between 35°- 60°.
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Subtropical Steppe (BSh) and Subtropical Desert (BWh) Climates
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- Both have common precipitation and temperature characteristics.
- Located in the transition zone between humid and dry climates, subtropical steppe receives slightly more rainfall than the desert, adequate enough for the growth of sparse grasslands.
- The rainfall in both the climates is highly variable.
- The variability in the rainfall affects the life in the steppe much more than in the desert, more often causing famine.
- Rain occurs in short intense thundershowers in deserts and is ineffective in building soil moisture.
- Fog is common in coastal deserts bordering cold currents.
- Maximum temperature in the summer is very high. The highest shade temperature of 58° C was recorded at Al Aziziyah, Libya on 13 September 1922.
- The annual and diurnal ranges of temperature are also high.
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Warm Temperate (Mid-Latitude) Climates-C
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- Extend from 30° – 50° of latitude mainly on the eastern and western margins of continents.
- These climates generally have warm summers with mild winters.
- They are grouped into four types:
- Humid subtropical, i.e. dry in winter and hot in summer (Cwa);
- Mediterranean (Cs);
- Humid subtropical, i.e. no dry season and mild winter (Cfa);
- Marine west coast climate (Cfb)
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Humid Subtropical Climate (Cwa)
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- Occurs pole ward of Tropic of Cancer and Capricorn, mainly in North Indian plains and South China interior plains.
- The climate is similar to Aw climate except that the temperature in winter is warm.
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Mediterranean Climate (Cs)
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- Occurs around Mediterranean sea, along the west coast of continents in subtropical latitudes between 30° – 40° latitudes
- Central California, Central Chile, along the coast in south eastern and south western Australia.
- These areas come under the influence of sub tropical high in summer and westerly wind in winter.
- Hence, the climate is characterised by hot, dry summer and mild, rainy winter.
- Monthly average temperature in summer is around 25° C and in winter below 10°C.
- The annual precipitation ranges between 35 – 90 cm
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Humid Subtropical (Cfa) Climate
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- Lies on the eastern parts of the continent in subtropical latitudes
- In this region the air masses are generally unstable and cause rainfall throughout the year.
- They occur in eastern United States of America, southern and eastern China, southern Japan, north- eastern Argentina, coastal south Africa and eastern coast of Australia.
- The annual averages of precipitation vary from 75-150 cm.
- Thunderstorms in summer and frontal precipitation in winter are common.
- Mean monthly temperature in summer is around 27°C, and in winter it varies from 5°-12° C.
- The daily range of temperature is small.
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Marine West Coast Climate (Cfb)
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- Located poleward from the Mediterranean climate on the west coast of the continents.
- The main areas are: North- western Europe, west coast of North America, north of California, southern Chile, south- eastern Australia and New Zealand.
- Due to marine influence, the temperature is moderate and in winter, it is warmer than for its latitude.
- The mean temperature in summer months ranges from 15°-20°C and in winter 4°-10°C.
- The annual and daily ranges of temperature are small
- Precipitation occurs throughout the year. Precipitation varies greatly from 50-250cm.
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Cold Snow Forest Climates (D)
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- Occur in the large continental area in the northern hemisphere between 40°-70° north latitudes in Europe, Asia and North America.
- Cold snow forest climates are divided into two types-
- (i) Df- cold climate with humid winter;
- (ii) Dw- cold climate with dry winter. The severity of winter is more pronounced in higher latitudes.
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Cold Climate with Humid Winters (Df)
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- Occurs poleward of marine west coast climate and mid latitude steppe. The winters are cold and snowy.
- The frost free season is short.
- The annual ranges of temperature are large.
- The weather changes are abrupt and short.
- Poleward, the winters are more severe.
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Cold Climate with Dry Winters (Dw)
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- Occurs mainly over North- eastern Asia
- The development of pronounced winter anti cyclone and its weakening in summer sets in monsoon like reversal of wind in this region
- Poleward summer temperatures are lower and winter temperatures are extremely low with many locations experiencing below freezing point temperatures for up to seven months in a year
- Precipitation occurs in summer
- The annual precipitation is low from 12-15 cm
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Polar Climates (E)
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- Poleward beyond 70° latitude.
- Polar climates consist of two types:
- (i) Tundra (ET); (ii) Ice Cap (EF).
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Tundra Climate (ET)
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- The tundra climate (ET) is so called after the types of vegetation, like low growing mosses, lichens and flowering plants.
- This is the region of permafrost where the sub soil is permanently frozen.
- The short growing season and water logging support only low growing plants.
- During summer, the tundra regions have very long duration of day light.
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Ice Cap Climate (EF)
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- Occurs over interior Greenland and Antarctica
- Even in summer, the temperature is below freezing point.
- This area receives very little precipitation.
- The snow and ice get accumulated and the mounting pressure causes the deformation of the ice sheets and they break.
- They move as icebergs that float in the Arctic and Antarctic waters.
- Plateau Station, Antarctica ,79°S, portray this climate.
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Highland Climates (H)
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- Governed by topography
- In high mountains, large changes in mean temperature occur over short distances.
- Precipitation types and intensity also vary spatially across high lands.
- There is vertical zonation of layering of climatic types with elevation in the mountain environment.
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Greenhouse Gases (GHGs)
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- Carbon dioxide (CO2), Chlorofluorocarbons (CFCs), methane (CH4), nitrous oxide (N2O) and ozone (O3)
- Some other gases such as nitric oxide (NO) and carbon monoxide (CO) easily react with GHGs and affect their concentration in the atmosphere.
- The effectiveness of any given GHG molecule will depend on the magnitude of the increase in its concentration, its life time in the atmosphere and the wavelength of radiation that it absorbs.
- The chlorofluorocarbons (CFCs) are highly effective.
- Ozone which absorbs ultra violet radiation in the stratosphere is very effective in absorbing terrestrial radiation when it is present in the lower troposphere.
- The largest concentration of GHGs in the atmosphere is carbon dioxide.
- The emission of CO2 comes mainly from fossil fuel combustion (oil, gas and coal).
- Forests and oceans are the sinks for the carbon dioxide.
- Forests use CO2 in their growth. So, deforestation due to changes in land use, also increases the concentration of CO2.
- Doubling of concentration of CO2 over pre-industrial level is used as an index for estimating the changes in climate in climatic models.
- The CFCs which drift into the stratosphere destroy the ozone. Large depletion of ozone occurs over Antarctica.
- The depletion of ozone concentration in the stratosphere is called the ozone hole.
- This allows the ultra violet rays to pass through the troposphere.
- International efforts have been initiated for reducing the emission of GHGs into the atmosphere.
- The most important one is the Kyoto protocol proclaimed in 1997.
- This protocol went into effect in 2005, ratified by 141 nations.
- Kyoto protocol bounds the 35 industrialised countries to reduce their emissions by the year 2012 to 5 % less than the levels prevalent in the year 1990.
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Global Warming
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- Due to the presence of greenhouse gases, the atmosphere is behaving like a greenhouse.
- The atmosphere also transmits the incoming solar radiation but absorbs the vast majority of long wave radiation emitted upwards by the earth’s surface.
- The gases that absorb long wave radiation are called greenhouse gases.The processes that warm the atmosphere are often collectively referred to as the greenhouse effect.
- The term greenhouse is derived from the analogy to a greenhouse used in cold areas for preserving heat.
- A greenhouse is made up of glass. The glass which is transparent to incoming short wave solar radiation is opaque to outgoing long wave radiation.
- The glass, therefore, allows in more radiation and prevents the long wave radiation going outside the glass house, causing the temperature inside the glasshouse structure warmer than outside.
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Orographic Rain
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- When the saturated air mass comes across a mountain, it is forced to ascend and as it rises, it expands; the temperature falls, and the moisture is condensed.
- The chief characteristic of this sort of rain is that the windward slopes receive greater rainfall.
- After giving rain on the windward side, when these winds reach the other slope, they descend, and their temperature rises.
- Then their capacity to take in moisture increases and hence, these leeward slopes remain rainless and dry.
- The area situated on the leeward side, which gets less rainfall is known as the rain-shadow area.
- It is also known as the relief rain.
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Convectional Rain
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- The, air on being heated, becomes light and rises up in convection currents.
- As it rises, it expands and loses heat and consequently, condensation takes place and cumulous clouds are formed.
- With thunder and lightning, heavy rainfall takes place but this does not last long.
- Such rain is common in the summer or in the hotter part of the day.
- It is very common in the equatorial regions and interior parts of the continents, particularly in the northern hemisphere.
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