Home General Knowledge GEOGRAPHY NOTES : WORLD CLIMATIC TYPES & WORLD OF OCEANS
GEOGRAPHY NOTES : WORLD CLIMATIC TYPES & WORLD OF OCEANS
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Saturday, 18 January 2014 07:57


WORLD CLIMATIC TYPES & WORLD OF OCEANS


WORLD CLIMATIC TYPES

TROPICAL RAIN FOREST/EQUATORIAL CLIMATE

1. Prevails mainly between 10o N and 10o S of equator.

2. Found in the Amazon lowlands (S. America), Congo Basin (Africa), Madagaskar and East Indies (from Sumatra to New Guinea).

3. Rainfall mostly convectional occurs throughout the year.

4. Annual rainfall is about 200 cm, though some regions get heavier rains.

5. Climate is consistently moist with no month recording less than 6 cm of rainfall.

6. Mean monthly temperature ranges between 24o and 27o C.

7. Annual ranges of temperature commonly less than 2o to 3o C.

8. Diurnal range of temperature is more, i.e. 6o to 8o C.

9. A region of great biodiversity – abundance of flora and fauna.

10. Diseases and insects, harsh climate and dense forests pose hindrance to economic development.

 

TROPICAL MONSOON CLIMATE

1. Within the tropics in the eastern sides of the continents.

2. Spreads over South, South-East and East Asia (India, Myanmar, South China) and Northern Australia.

3. Dominant characteristics – complete reversal of prevailing wind direction from season to season coastline 7516 km. (including the coastline of Andaman Nicobar and Lakshadweep islands).

4. Average annual rainfall about 150 cm.

5. Rainfall highly erratic, mainly in summer season.

6. Average temperature of summer is 30o C and of winter is 15o C.

7. A distinct dry season (in winter) one or more months with rain less than 6 cm.

8. Forests are rich in Sal, Teak,Shisham & Bamboo.

 

TROPICAL GRASSLAND / SAVANNA/ SUDAN CLIMATE

1. Found between 5o and 15o North and South.

2. Transitional zone between the equatorial & Monsoon on the one hand and arid & semi-arid climates on the other.

3. Found in Africa (north & south of Equatorial belt), East-Central South America (Lianos in Columbian Highland, Campas in Brazil), Northern Australia and some parts of India (man-Induced).

4. High temperature throughout the year.
5. Average annual temperature is more than 25o C.
6. High summer temperature around 32o C while winter temperature is about 21o C.

7. Annual range of temperature 11o C.

8. A distinct dry season in winter when the region comes under the influence of trade winds.

9. Average annual rainfall around 75 cm, rainfall mainly in summer (mainly of convectional type).

10. Natural vegetation comprises toll grasses with scattered trees, called ‘Parkland Vegetation’.

 

DRY TOPICAL (DESERT) CLIMATE

1. Found on the western margins of continents along the Tropic of Cancer and Tropic of Capricorn.

2. Chief regions are Sahara desert (Africa), Great Australian Desert, Arabian, Iranian and Thar Desert in Asia, Kalahari & Namib Deserts (Africa), Mohava Desert in North America and Atacama Desert in South America.

3. The main cause of aridity is their location in the sub-tropical high pressure belt and the effect of dry offshore trade winds on the western margins of continents.

4. Mean summer temperature around 30o C and mean winter temperature about 10o C.

5. Diurnal temperature ranges are very high – from 15o C to 40o C.

6. Highest temperatures have been recorded in this climate e.g. 58.7o C in Al Azizia (Libya), 58o C in Death Valley, 52o C Jacobabad (Pakistan) of Thar.

7. Annual rainfall very low, about 12 cm, rainfall highly variable.

8. Vegetation is of nerophytic type.

 

TEMPERATE WESTERN MARGIN / MEDITERRANEAN CLIMATE

1. Found between 30o and 45o latitude in both the Hemisphere on the western side of each continent.

2. Its typical areas are around the shores of Mediterranean Sea, South-West Africa (Cape region), Central Chile, Central California and South-west and Southern Australia (Adelaide to Melbourne).

3. Pre-dominant characteristic is dry summer and mild moist water.

4. Summer is dry because trade winds blow offshore.

5. But in winter the region comes under the influence of onshore westerlies due to shifting of the pressure belts towards equator. These westerlies bring winter rainfall here.

6. Annual rainfall varies between 50 and 75 cm.

7. Summer temperature ranges between 20 and 27o C, while the winter temperatures are 4o to 10o.

8. This climate experiences hot dusty wind of Sirocco and cold winds of Mistral (France) and Bora (Yugoslavia).

9. This climatic region is noted for its orchard farming of citrus fruits, especially viticulture (grape farming).

 

TEMPERATE CONTINENTAL (STEPPE)/WARM TEMPERATE INTERIOR CLIMATE

1. Located in the interiors of the continents due to which they do not get sufficient rainfall from the westerlies.

2. Spreads over the temperate grassland regions of the world, i.e. Steppes of Eurasia, Prairies of North America, Velds of South Africa, Pampas of South America, Downs of Australia, Canterbury Grasslands of New Zealand and Pustaz of Hungary.

3. Warm summer with about 20o C temperature and cold winter with about 5o - 10o C.

4. Average annual rainfall ranges between 25 cm and 75 cm.

5. Rainfall mostly in summer.

6. Grasslands are practically treeless.

 

DRY MID-LATITUDE TEMPERATE CLIMATE

1. Found between 30o and 45o latitudes in the interiors of continents.

2. Main areas are Gobi, Tibet, Mangolia and Turkistan in Central Asia, Patagonia in South America.

3. Diurnal ranges of temperature upto 50o C.

4. Annual range of temperature is low (high).

5. Rainfall scanty, about 12 cm.

6. Main cause of aridity is interior location or inter-montane location.

 

WARM TEMPERATE EASTERN MARGIN / CHINA TYPE CLIMATE

1. Found on the eastern margin on continents between 25o and 45o N and S.

2. Chief regions are Eastern & Central China, S.E. America and South Eastern parts of Africa and Australia, S. Brazil and S. Japan.

3. Average summer temperature sf 26o C while average winter temperature is 13o C.

4. 70 per cent or more of the mean annual rainfall in warmer six months.

5. Warmest month of summer has at least 10 times the precipitation of the driest month of winter. Average annual rainfall is 100 cm.

6. Pampero (Argentina) & Southerly Buster (Australia) are cold local winds blowing in this climate.

7. Tropical cyclones e.g. Typhoons (S. China) & Hurricanes (S.E. USA) are common in summer.

8. Normally mixed coniferous and broad-leaved forest are found.

 

COOL TEMPERATE WESTERN MARGIN / WEST EUROPEAN CLIMATE

1. Prevails along the western margins of continents between 45o and 60o latitudes in both the hemispheres.

2. Representative areas are N-W Europe, Western Canada, Southern Chile, Southern Chile, Southern Island of NewZealand and Tasmania.

3. Rainfall throughout the year, but more in winter.

4. The region come under the permanent westerly winds which blow from the oceans keeping the climate moist   throught the year.

5. Total annual rainfall – 100 cm, rainfall mainly cyclonic.

6. Mean winter temperature is 5o C while that of summer is 15o C.

7. The annual temperature ranges are not high, i.e. 80 degrees C to 110 degrees C caused by the combined effect of warm ocean currents (North Atlantic and N. Pacific Drifts) and winds.

8. Both deciduous and coniferous forests are found.

 

COOL TEMPERATE CONTINENTAL / TAIGA CLIMATE

1. Extends from 45o to 70o latitude in Northern Hemisphere.

2. From Alaska to New Found Land in North America and from Norway to Kamchatka in Eurasia.

3. Greatest annual range of temperature of over 55o C is found here.

4. The summer temperature is around 15o to 20o while winter temperature range from - 34o C in Canada to 45o C in parts of CIS.

5. Summer is short (4-5 months) while winters are long.

6. Annual rainfall is 25 – 50 cm, mostly in summer.

7. This climate is distinct for its evergreen coniferous forest or Boreal Forest Biome.

 

TUNDRA CLIMATE

1. North of 70o latitude in North America & Eurasia, coastal tract of Iceland and Greenland.

2. Warmest month temperature is below 10o C but more than 0o C, average annual temperature is -12o C, annual range of temperature is 39o to 50o C.

3. Mean annual precipitation, mostly in the form of snowfall, is below 40 cm.

4. Vegetation comprises lichens & mosses supported by characteristic lithosols of Tundra.

 

HIGHLAND CLIMATE

1. Alll the mountain regions of the world have 1500 metre height.

2. Temperature decreases with altitude, therefore vertical zonation of climate, from tropical to ice-cap type.

3. Rainfall on windward slopes, leeward sides are dry.

 

THE WORLD OF OCEANS

  • Oceans extend over 70.8 per cent part of the earth’s surface.
  • About 60.7 per cent part of the Northern Hemisphere is covered by oceans while 80.9 per cent surface area of the Southern Hemisphere is occupied by the oceans.
  • Total area of the earth is about 510 million km2 of which about 360 million km2 (70.8 per cent) is represented by the seas and oceans.
  • Oceans with their vast extent have a profound impact on the climatic phenomenon of the world. They work as the repositories of the solar energy. Oceanic currents are one of the chief means of the distribution of temperature on the earth. Almost all of rainfall on the content is caused by the moisture drawn from the oceans.
  • The elevation of the landmasses and the depth zones of oceans are represented by the Hysographic or Hypsometric curve which shows these regions as percentage of the area of the globe.

 

OCEAN BOTTOM RELIEF

  • The study of the ocean bottom relief features has shed immense light on the origin and evolution of earth’s crust and the theory of plate tectonics.
  • The mean elevation of the land surface is 840 metres while the average depth of oceans is more than 4.5 times, i.e. 3,800 metres.

 

I. CONTINENTAL SHELF

(i) The shallow submerged extension of the continent is called the continental shelf.

(ii) Average depth – 100 fathoms (200 metres); average slope – 17 feet /mile or about 1o.

(iii) Average width – 70 km;

(iv) Continental shelf covers 7.5 per cent area of the oceans. It extends over 13.3 per cent part of the Atlantic Ocean, 5.7 per cent part of Pacific Ocean and 4.2 per cent part of Indian Ocean.

(v) Narrow Shelves occur where mountains are found along the coasts e.g. along the Andean coasts.

(vi) Continental shelf of the western coast of India is wider than that of eastern coast, mainly because of the subsidence of the western continental part.

(vii) Continental shelves represent the rich fishing grounds of the world and they also contain other marine foods, metallic nodules, petroleum and natural gas etc.

 

II. CONTINENTAL SLOPE

(i) Sea – ward part adjacent to continental shelf having steep slope.

(ii) Average slope – 20 to 50 degrees.

(iii) Depth – 200-2,000 fathoms (3,660 metres).

(iv) An important feature of continental slope is the existence of steep submarine canyons on them.

III.    CONTINENTAL RISE

(i) Average Slope – 0.5o to 1o;

(ii) With increasing depth it becomes almost flat and merges with abyssal plain.

 

IV.    DEEP SEA/ABYSSAL PLAINS

(i) Average depth – 3,000 to 6,000 metres

(ii) Very low slope gradient (1:100)

(ii) Covers 75.9 per cent of total oceanic area including 80.3 per cent of Pacific, 80.1 per cent of Indian   Ocean & only 54.9 per cent of Atlantic.

(iii) The main reason for lesser extent of abyssal plains in the Atlantic is the existence of wide continental shelves and slopes.

 

V.     DEEPS / TRENCHES

(i) Deepest part/feature of the oceanic floor.

(ii) Usually parallel to the coasts and island areas and not in middle of the oceans.

(ii) Tectonic in origin, represents the site of sub ducting plate boundary.

(iii) Mariana trench (Challenger deep) is the deepest trench in the world situated in the N.W. Pacific oceans.

 

VI.    OCEANIC RIDGES

(i) It is thousands of km long and hundreds of km wide mountain range on the oceanic floor.

(ii) These ridges have been formed by volcanic activity along the spreading boundary of plates.

(ii) Their summits may rise above the sea level in the form of islands e.g. Iceland, Azores island, etc.

 

VII.  SEA MOUNTS AND GYOTS

(i) Sea mounts are submarine hills which rise above the oceanic floor upto 1000 metres.

(ii) Flat topped sea mounts are called gyots.

(iii) Both have been formed by the volcanic activity.

(iv) Largest number of sea mounts and gyots are found in the Pacific.

 

VIII. SUBMARINE CANYONS

(i) Deep gorge like features on the ocean floor are called submarine canyons.

(ii) They are deep valley having very steep slopes, confining of the continental shelf, slope and rise.

(iii) Many submarine canyons are found along the mouths of major rivers, e.g. Hudson canyon.

 

IX. BANK, SHOAL, AND REEF

(i) Flat-topped elevations located in the shelf and slope area are known as banks. Adequate water depth exists for navigation. They represent world’s famous fishing grounds such as Grand Bank (Atlantic),   Dogger Bank (North Sea), etc.

(ii) Detached elevations with shallow depth are called shoals which are dangerous for navigation.

(iii) Coral reefs are formed by the skeletal remains of the coral organisms. These organic deposits are rich in calcareous matter. Many islands are formed by the coral deposits. ‘Great Barrier Reef’ off the N.E. coast of Australia is the largest one.

 

OCEAN TEMPERATURE

  • Usually the temperature of oceanic water ranges from -5o C to 33o C.
  • Mean diurnal range of temperature of oceanic surface water is almost negligible (about 1o C).
  • The maximum annual temperature of Northern Hemisphere is recorded in August and lowest in February.
  • High annual range of temperature is found in land-locked seas e.g. 200o F in Mediterranean Sea and 40o F in Baltic Sea.
  • Atlantic Ocean exhibit more annual range of temperature than Pacific because of its smaller size.
  • The warm Gulf Stream current does not allow the Norwegian coast to feeze even in winter.

 

SALINITY

  • Salinity is defined as the total amount of salt particles in grams contained in one kg of sea water and is expressed as part per thousand (%o).
  • Salinity affects the physical properties of the oceans such as temperature, density, pressure, currents, etc.
  • More saline water freezes slowly while the boiling point of saline water is higher than the fresh water. Evaporation is lower over more saline water. Salinity also increases the density of water.

 

SALT IN THE SEA

Salt

Percentage

Sodium Chloride (NaCl)

77

Magnesium Chloride (MgCl)

10.9

Magnesium Sulphate (MgSO4)

9.7

Calcium Sulpahte (CaSO4)

3.6

TIDES

  • The rise of sea water and its movement towards the coast is called tide and the resultant high water level is known as high tide water.
  • The fall of sea water and its movement towards the sea is called ebb and the resultant low water level is called low tide water.
  • Tides vary from place to place because of:

(i) The change in the position of the sun and the moon in relation to earth.

(ii) Uneven distribution of water over the globe.

(iii) Irregularities in the configuration of oceans.

  • The moon though a smaller heavenly body, exerts a greater influence on tides because of its lesser distance from the earth than that of the sun.
  • The sun, the moon and the earth come in a straight line on the full moon and the new moon and therefore the gravitational forces of the sun and the moon work together producing very high tide, called spring tide.
  • The position of the sun, the moon and the earth in a straight line is called synergy.
  • When the sun and the moon are in a straight line, the position is called conjunction. When the position of the earth is in between the sun and the moon, it is called opposition. The positon of conjunction and opposition take place during new moon and full moon respectively.
  • The sun, the earth and the moon come in the position of a right angle (called quadrature) on seventh or eighth day of every fortnight of a month and thus the tide producing forces of the sun and the moon work in opposite directions; as a result low tide is caused. Such tides are called neap tides.

 

TIME OF TIDES

  • Generally tides occur twice a day. But Southampton, along the southern coast of England experiences tides four times a day because the tidal water comes through the English Channel and through the North Sea at different intervals.

 

OCEAN CURRENTS

  • Ocean currents are large masses of surface water that circular in regular patterns around the oceans.
  • The planetary winds have probably the most dominant influence on the flow of ocean currents.
  • Between the equator and the tropics blow the trade winds which move equatorial waters westwards and polewards and warm the eastern coast of continents.
  • In the temperature latitudes blow the westerlies which result in a north easterly flow of water in the northern hemisphere and to the left in the southern hemisphere.

 

CORAL REEFS

  • Coral reefs are masses of lime stone and dolomite accumulated by limepsecreting organism known as coral polyps.

 

TYPES OF CORAL REEFS

(i) Fringing Reefs: There are narrow belts of coral reefs developed along the continental margins. They are usually attached to the coastal land but occasionally theyare separated from the shore by a shallow and narrow lagoon called ‘Boat Channel’.

 

(ii) Barrier Reefs: Largest coral reefs off the coastal platforms but parallel to them. The reef lies at a distance away from the coast. Hence a broad lagoon develops between the reef and the shore. Great Barrier Reef off the coast of N-E Australia (1200 miles long) is a famous example.

 

(iii) Atolls: They are circular or horse-shoe shaped, enclosing a lagoon often without any central island. The depth of the lagoon is few metres only with sand and limestone debris at the bottom. Funafuti atoll of Ellice Island is a famous atoll.



 

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