Evaporation and Condensation
➤ Evaporation is the process by which water is transformed from liquid to gaseous form.
➤ It takes approximately 600 calories of energy to convert one gram of water to water vapour.
➤ One calorie is the amount of heat required to raise the temperature of one gram of water to 1°C.
➤ Condensation is the process of change of state from gaseous to liquid or solid state.
➤ Dew, white frost, fog, mist and clouds are various forms of condensation.
➤ When the moisture is deposited in the form of water droplets on cooler surface of solid objects such as stones, grass backs and plant leaves, it is known as dew.
➤ The ideal conditions for dew formation are : a clear sky, little or no wind, high relative humidity and cold and long nights.
➤ When condensation takes place at a dew point which is at or below freezing point, excess moisture is deposited in the form of minute ice crystals. It is called as white frost.
➤ Fog is defined as a cloud with its base at or very near the ground.
Fogs are of different kinds depending upon the nature of the cooling process.
➤ Mist is also a kind of fog in which the visibility is more than one km but less then 2 km.
➤ Cloud is a mass of minute droplets of water or tiny crystals of ice formed by the condensation of the water-vapour in free air at considerable elevations.
➤ Generally there are ten major types of clouds which are grouped under three main categories arranged according to their height.
➤ Humidity is the general term which describes the invisible amount of water vapour present in the air.
➤ Absolute Humidity is the weight of actual amount of water vapour present in a unit volume of air. It is expressed as grams per cubic meter of air.
➤ Specific Humidity is the weight of water vapour per unit weight of air. It is expressed as grams per kilogram of air.
➤ Relative Humidity is the ratio of the air’s actual water vapour content to its water vapour capacity at a given temperature. It is expressed in percentage.
➤ Dew point is the temperature at which saturation occurs.
Three main categories of clouds :
1. Cirrus clouds – Forms around 12 km altitude.
2. Altostratus clouds – forms around 6 km altitude.
3. Stratocumulus clouds – forms at low altitude around 2.1 km.
➤ Condensation of water vapour in the air in the form of water droplets and ice and their falling on the ground is called precipitation.
➤ The precipitation in the form of drops of water is called rainfall.
➤ When the temperature is less than O°C precipitation takes place in the form of fine flakes of snow and is called snow-fall.
➤ Sleet is frozen raindrops and refrozen
➤ Precipitation in the form of hard rounded pellets is known as hail.
➤ On the basis of its origin precipitation may be classified into three main types :
(i) Convectional Precipitation :
It is caused when moist winds are drawn into the convection currents of a hot region. It generally occurs in equatorial region. The thundery rain of a summer afternoon is a typical example.
(ii) Orographic Precipitation :
It is caused by the surface relief of the land, mainly, by the presence of mountain range. There is heavy rain on the wind-ward side.
(iii) Cyclonic Precipitation : It is associated with the passage of a cyclone or depression.
Forest in the World
➤ According to a recent global assement forests cover 31% of the total land area of the World.
➤ The average land area per capita is 0.6 hectare.
➤ The total forest areas in 2016 was around 4 billion hectares.
World Climatic Zones
1. Equatorial Climate Or Tropical Rain Forest
➤ It is found between 5°N to 10°N and South of equator.
Climate Location: South America : Largest area is in the Amazon lowlands. It also occurs along the coast of Guianas. Africa : Part of the Congo basin and Guinea coast Africa. Southern Asia : Malaysia, Indonesia, New Guinea and parts of Philippines.
➤ It is warm round the year as the sun’s rays are always fall vertically. Annual average temperature is uniform at 27°C. The daily range of temperature is in between 10°C and 25°C. The annual range temperature is less than 5°C.
➤ This region has no dry season. Average annual rainfall is 200 cm to 250 cm.
➤ Thermally included low pressure belt due to the uniform high temperature throughout the year.
➤ Convection current is formed and results in rainfall in this zone.
➤ The convergence of trade winds coming from sub-tropical high pressure belt forms intertropical convergence (ITC). ITC is associated with atmospheric distribution (cyclone).
Vegetation High temperature and rain throughout the year produce most luxuriant vegetation in the region which are tropical rainforest or Selvas in South America.
2. Savanna Or Sudan Type
This transitional type of climate is bounded between equatorial rainforest and semi-arid and subtropical humid climate. This lies between 5° to 20° north and south of equator.
South America : Columbia and Venezuela. Africa : Sudan, parts of Senegal, Mali, Guinea, Niger, Chad, Ghana, Togo, Kenya, Zimbabwe, Tanzania, Angola and Uganda. Australia : Queensland.
➤ This zone has distinct wet and dry season.
➤ Annual precipitation of 100 cm to 150 cm is received.
➤ 80% to 90% of the rain occurs in rainy season only.
➤ Seasonal rains allow grass to grow. These are natural grasslands. Rainfall is not sufficient to support tall trees but grass grows well. Elephant grass grows up to 4.5 metres. As we move towards the equator, trees with broad leaf and umbrella shaped grow along the banks of the streams.
➤ Fauna: Elephants, giraffe, zebra, rhinoceros along with varieties of carnivores animals (lion, leopards, tiger, cheeta, hyena etc.) are found.
3. Hot Desert
Arid deserts lie close to the tropic of cancer and tropic of capricorn in the western margins of continents, between 15°-30° in both the hemispheres.
➤ Sahara, Arabia, Thar, Mohave and Sonoran (U.S.A.), Kalahari and Namib (Africa), Simpson, Gibson, Great Sandy (Australia). These lie in western part of the continents.
➤ Climate is dominated by subsidence of air masses and sub tropical anti cyclones.
➤ These areas are nearly rainless or receive lowest annual rainfall (Less than 12 cm).
➤ Normal vegetation is cactus, thorny plants, shrubs and herbs.
4. Steppe (Temperate Continental) Climate
These are also called mid-latitude grasslands. They are far away from any influence of the sea as they are in the heart of the continents. Examples: • Prairies (North America), Pampas (South America), Velds (South Africa), Canterbury (Newzeland), Downs (Australia) and Steppes (Russia).
➤ Their climate is continental with extremes of temperature. Summers are very warm and winters are very cold. In northern hemisphere where as in southern hemisphere the temperature variation is mild.
➤ These are dry lands as they are located in the deep interiors of large land masses away from the oceans.
Rain fall occurs in spring and early summer and varies between 25 cm. and 75 cm. Rain in this region is of convectional type and light.
Vegetation Short grass grows everywhere. Trees are found only on mountain slopes.
➤ The zone lies between 30°-40°N and Southern latitudes on the western edge of the continents. Mediterranean type of climate is found near the Mediterranean sea in the northern hemisphere (Portugal to Turkey, Morocco, Northern Algeria, Tunisia and Libya) alongwith southern California coast.
➤ In the southern hemisphere central Chile, Capetown area of South America, South and Southwest coast of Australia.
➤ The zone experiences season shift of pressure belt
➤ Winter rainfall is received through cyclonic storms.
➤ Summer winds are generally dry and hot.
➤ Woodland, dwarf forest and scrubs are found in this region.
➤ The leaves are thick and shiny resisting moisture loss.
➤ The trees like pine, oak, cedar, madrone, walnut and chestnuts grows here.
➤ Citrus fruits are grown in this zone.
6. Sub-Tropical Humid Climate/China Type Location
➤ It is found in the eastern boundary of the all continents between 25°C to 40° N and Southern latitude.
➤ It is found in south-east China, PO Basin, Danube Basin, South-east USA; south-east Brazil, Paraguay, Uraguay and north-eastern Argentina and Africa alongwith the east coast of Africa.
➤ Mean annual summer temperature lies between 24°C to 26° and during winter it is 6.6°C to 10°C.
➤ The temperature do not varies spatially.
➤ Tropical cyclone is found and results in rainfall. Even winter cyclones are found here as it is associated with Westerlies.
➤ Dense evergreen forests are found alongwith decid
➤ us sparse forest and grassland. They have broad leaves.
7. West European Type
➤ The zone lies between 40° and 65° latitude in both the hemispheres along the west coast of the continents. North-Western Europe, British Columbia of Canada, Washington and Oregon states of the USA, south-west coast of Chile, south-east coast of Australia and Tasmania and New Zealand.
➤ Polar front causes the development of temperate cyclone in this region under the influence of westerlies.
➤ Broad-leaf deciduous forests (oak, birch, walnut, maple, elm, chestnut, etc).
➤ Needle-leaf (coniferous) forests like pine, fir etc are found.
➤ Mixed forest is also found here.
➤Monsoo n region includes the eastern margins of continents which lies between 5° to 30° N and Southern latitude of equator.
➤ Eastern Brazil (S. America), Central American countries, Natal coast (S. Africa), Indian subcontinent, South East Asia, Myanmar, Thailand, Vietnam, Philippines, etc. Parts of East Africa including Malagasy and North Australia.
➤ Temperature variation results in season formation.
➤ During the months of summer (March to June) the average temperature is ranging between 27°C to 32°C.
➤ During the months of winter the average temperature recorded is 10° to 27°C.
➤ The temperature in this zone is controlled by nearness or remotness of the sea, latitudinal and altitudinal also influence it.
➤ The region receives cyclonic rainfall mostly alongwith orographic rain.
➤ 80% of the rainfall is received within 3 months (July, August and September).
➤ Monsoon rainfall is basically cyclonic in character.
➤ Generally, dry season is found here
Vegetation • Trees are mostly deciduous. The forests are open and less luxuriant. Most of the forests yield valuable timber like teak and other kinds of timber are sal, acacia and eucalyptus.
9. Taiga /Boreal/ Sub-Arctic
This climate type is named after the coniferous forest cover found in the region.
➤ This region lies between 55° and 70° in northern hemisphere. It forms a continuous belt across southern Canada, northern Europe and Russia.
➤ South Alaska, southern Canada, parts of Norway, Sweden, Finland, Northern Russia, Northern Siberia, and Sakhalin Island.
➤ Winters are very cold and severe lasting for 6 to 7 months .
➤ Most of the rain comes from cyclonic weather. It falls throughout the year but maximum in summer as frequent showers.
➤ In winter it is in the form of snow which remains on the ground for 5 to 7 months.
➤ Vegetation in this climate type is softwood coniferous forests (Spruce, fir, pine).
➤ Fauna like reindeer, deer, elk, moose and wild cat are found here.
➤ The northern most parts of Asia, Europe and North America (include Alaska and Canadian Islands).
➤ Long, bitterly cold and severe winter are experienced. Summers are short but cool. Precipitation is below 40 cm and as snowfall.
➤ Very short growing season. Dwarf willows and birches grow here. Fauna like reindeer, polar bear, fox, musk, ox and arctic hare are commonly found here.