COMPOSITION OF THE ATMOSPHERE • Atmosphere is a mixture of gases containing huge amount of solid and liquid particles collectively known as aerosols. Pure dry air consists of nitrogen, oxygen, argon, carbon dioxide, hydrogen, helium and ozone. Besides them, water vapour, dust particles, smoke, salts, etc. are also present in the air. • Nitrogen and oxygen comprise 99% of the total volume of the atmosphere. Nitrogen does not form a chemical union with other substances. It is an agent of dilution and regulates combustion. • Oxygen combines well with all other in the atmosphere elements. It is easily combustible. • Carbon dioxide exists in a very small percentage in the atmosphere. • It absorbs most of radiant energy emitted by earth and reradiates it back to the earth, creating green house effect. This increased the temperature of lower atmosphere. • It is also called as green house gas effect.
• The percentage of carbon dioxide in atmosphere increased due to burning of fossil fuels (coal, petroleum and natural gas) and deforestation. • Water vapour and dust particles are crucial to weather and climate. They create condensation and absorb the heat received from the sun and radiated from the earth. Water vapour comprises 3-4% of the total volume of air. • The amount of water vapour present in the atmosphere decreases from the equator towards the poles. Nearly 90% of the total water vapour lies below 6 km of the atmosphere.
STRUCTURE OF THE ATMOSPHERE The atmosphere consists of concentric layers of gases, with varying density and temperature. On the basis of chemical composition, the atmosphere is divided into: Homosphere and Heterosphere. 0 20 40 60 80 100 120 140 160 180 -200 –100 0 100 200 km TEMPERATURE °C Mesopause Mesosphere Stratopause Stratopause Troposphere Tropopause Thermosphere Heterosphere Homosphere B 1. Homosphere This extends up to the height of 90 km and is characterized by uniformity in chemical composition. It consists of three thermal layers – troposphere, stratosphere and mesosphere. (a) Troposphere Lowest layer of the atmosphere. • Height of troposphere is 16 km at the equator and 10 km at the poles. • Temperature decreases with height in this layer roughly at the rate of 1°C per 165 metres, which is known as normal lapse rate. • Upper limit of the troposphere is called tropopause. • All weather phenomena are restricted to troposphere. (b) Stratosphere • It lies above tropopause between 25-30 kms on an average over middle latitutde. 50 km is considered to be its upper limit on an average. • At 50 km of altitude the temperature becomes 0°C. • Stratosphere is more or less devoid of major weather phenomena but there is circulation of feable winds and cirrus cloud in its lower layer. • Bacteria is found to be surviving here. This is mainly due to presence of ozone (15-35 km) in lower stratosphere. • Ozone is blue irritating gas with pungent odour. • Upper limit of stratosphere is called as stratopause. • Commercial airlines cruise in lower stratosphere mostly due to low temperature, which results in optimum fuel burn and low density of air reduces parasitic drag on airframe. This layer even provide smooth movement as this layer has very less weather turbulence. (c) Mesosphere • It lies above the stratopause. • Mesosphere extends to 50-80 km. • The upper limit is called mesopause. • Temperature decreases with height and reaches a minimum of –110°C at 80-90 km in the mesopause. 2. Heterosphere Proportions of gases are not constant in this layer. (a) Thermosphere It lies beyond 80 km above mesopause. Here the temperature increases rapidly with increase in height. The gases become very light due to extremely low density. It divides into two layers: inosphere and exosphere. (i) Ionosphere lies between 80 km to 640 km above the sea level. There are number of ionic layers in the sphere, e.g. D layer, E layer, F layer and G layer. – D layer disappears with sunset as it is associated with solar radiation. – E layer is known as Kennelly-Heaviside, confined to the height between 99 km – 130 km. – It reflects the medium and high frequency radiowaves. – F2 layer is called as appleton layer, lying between 150 km-380 km. F1 and F2 area the two sub layers of E2 layer combinedly known as Appleton Layer. – G layer is beyond 400 km. (ii) Exosphere lies between 640 km above the sea level. Density becomes extremely low here and the atmosphere resembles as nebula because it is highly rarefied.
ATMOSPHERIC PRESSURE Air pressure is defined as total weight of a mass of column of air above per unit area at sea level. Air pressure is maximum at sea level. Pressure exerted by air at a particular point is determined by temperature and density. There is inverse relation between temperature and pressure. Air pressure is measured as a force per unit area. The unit of air pressure is milibar or mb measured by a barometer. The distribution of atmospheric pressure is shown on a map by isobars. An isobar is an imaginary line drawn through points of equal atmospheric pressure at the sea level. The spacing of isobars expresses the rate and direction of pressure change and is called pressure gradients. Major Pressure Belts • At the equator heated air rises creating a low-pressure area at the surface. This is called the equatorial low pressure. It is also known as doldrums. Reaching the troposphere the warm air bends towards the pole and descends at 30- 35° latitude or the tropics creating a belt of sub-tropical high pressure. • Subtropical high pressure zone is also known as horse latitude. Sub-tropical highs are the source of air moving along the surface towards the poles. • At 60-65° latitudes surface air streams coming from polar high pressure and sub-tropical high pressure converge and move up. This upward movement of air creates a low pressure system at the surface which is the sub-polar low pressure.
(i) Trade Winds Blowing from the subtropical highs or horse latitudes (between 30°N and 30°S) towards the equatorial low pressure are the trade wind. • In the northern hemisphere, the trade wind blowing from the northeast and is known as the Northeast trade wind in the southern hemisphere, the wind blowing from the southeast and are called the southeast trade wind. (ii) Westerlies Winds Prevailing wind in the middle latitudes between 35° and 65° latitude, blowing from high pressure area in the horse latitudes towards the poles are called as Westerlies wind. • The winds are predominantly from the southwest in the northern hemisphere and from the northwest in the southern hemisphere and bring extra-tropical cyclones with them. • In southern hemisphere they are stronger and more constant in direction than those of the northern hemisphere because of the vast expanse of water. • They are best developed between 40° and 65° south latitudes. These latitudes are hence often called Roaring forties, furious fifties and shrieking sixties. (iii) Polar Wind Winds blowing in the arctic and the antarctic latitudes are polar winds. They blow from polar high pressure towards sub-polar low pressure belt. In the northern hemisphere, they blow from north-east, and are called the north-east polar winds. In the southern hemisphere, they blow from south-east and are called south-east polar winds. As these winds blow from ice-capped landmass, they are very cold. 2. Periodic Winds Land and sea breezes local and monsoon winds are periodic winds. They are of the following types: (i) Seasonal Winds • Monsoon Winds: Monsoons are regional wind systems that predictably change direction with the passing of the seasons. Monsoons occur over distances of thousands of kilometers, and their two dominant patterns of wind flow act over an annual time scale. • South-West Monsoon: During summers, monsoon winds blow from cooler ocean surfaces onto the warmer continents during April to September. The continents become warmer than the oceans due to: (i) Specific heat differences between land and water. (ii) Greater evaporation over water surfaces. (iii) Subsurface mixing in ocean basins, which redistributes heat energy to a deeper layer. Precipitation is associated with summer monsoons. Onshore winds blowing inland from the warm ocean have very high in humidity. Upon cooling these air masses causes condensation and rain. Some highland in Asia receives more than 10 meters of rain during the summers. l North-West Monsoon: In the month of October and November the wind patterns reverses, as ocean surfaces are now warmer. With little solar energy available, continents begin cooling as long wave radiation is emitted to space. Ocean surface retains its heat longer as water has high specific heat and subsurface mixing. Winter monsoons bring clear dry weather and winds that flow from land to sea. It brings rain to A.P and T.N as they pick moisture from Ocean. l Monsoon Winds of SE Asia: Asiatic monsoon is caused by a complex climatic interaction between distribution of land, water, topography, and tropical and mid-latitudinal circulation. l During summer, a low-pressure forms over northern part of India and Southeast Asia because of high solar insolation. l Warm moist air is drawn into the thermal lows from air masses over the Indian Ocean. l Summer heat creates a strong latitudinal pressure gradient and development of an easterly jet stream (15 km) at the latitude of 25°N. l The jet stream enhances rainfall in Southeast Asia, Arabian Sea, and South Africa. When autumn returns to Asia, thermal extremes between land and ocean decrease. Westerlies of the mid-latitudes move in. Easterly jet stream is replaced with strong westerly winds in the upper atmosphere. Subsidence from an upper atmosphere cold low above the Himalayas produces outflow that creates a surface high-pressure system that dominates the weather in India and Southeast Asia. Besides, Asian continent, monsoon wind systems exist in Australia, Africa, South America, and North America. (ii) Local winds: Winds flow in comparatively small area and have special characteristics. They are generated by purely local factors (local temperature differences) and their zone of influence is quite limited. They play an important role in the weather of a particular locality. (iii) Land and Sea Breezes: Sometimes local conditions may set air in continuous motion. Even in calm days in summer, heated air rising from land surface may cause strong breezes to move in from over the cooler sea. By night, land cools more rapidly than the sea, cool air may move seawards as land breeze, usually a gentle flow. In some countries, if hot deserts border the seas, strong winds may develop. Sea breeze will be felt miles inland. Jet Streams: These are strong, rapid and narrow air currents circumpolar westerlies blowing in upper atmosphere or into troposphere. • Blow from west to east spreading over a few hundred kilometers at the height of 7.5-14 km • Found between poles and 20° latitude in both the hemisphere. The minimum velocity is 108 km/hr and the average summer velocity is 130 km/hr and average winter velocity is 65 km/hr. The maximum velocity is 480 km/hr.
Life Cycle of Cyclone The period of cyclone from its inception (cyclogenesis) to its termination (eyclolysis) is called as life cycle of cyclone. There are six stages in a life cyclone of a cyclone 1. First stage involves the convergence of two air masses of contrasting physical properties and direction. 2. Second stage is a stage when the warm and cold air masses penetrate into the territories of one other, and a wave-life front is formed. It is also called incipient stage. 3. Third stage is the mature stage when the cyclone is fully developed and the isobars are almost circular in shape. 4. Fourth stage in this stage where warm air mass is narrowed by the cold air mass. 5. Fifth stage is related with the starting of occlusion of cyclone. Here, the cold front fully overtake the warm front. 6. Sixth stage warm sector completely disappears and occluded front is eliminated and ultimately cyclone dies out. (2)Tropical Cyclone The development of the cyclone over the tropical region lying between tropic of cancer to capricorn are called as Tropical Cyclones. • Its average diameter varies between 80 km to 300 km. At times it is restricted to 50 km or even less in diameter. • Velocity varies between 32 km/hr to 180 km/hr or more when it is coverted into a hurricane. • Tropical cyclone becomes more vigorous and move with high velocity over ocean but over land it becomes feeble as it reaches interior portion of the continents. • There are less number of isobars and are more or less in circular shape. This results in rapid rush of wind towards the centre. • Every year it occurs at a particular period of a year, mainly during summer season. • It is not generated near equator as the coriolis force is negligible at equator. Types of Tropical Cyclone Tropical cyclone are divided into 4 major types: (1) Tropical disturbance (2) Tropical depression (3) Tropical storms (4) COMPOSITION OF THE ATMOSPHERE 1. Tropical disturbance It is associated with easterly trade wind. The easterly wave develops between 5° to 20° N latitude in the western part of the oceans. It is associated with large amount of cumulus or cumulonimbus cloud. These clouds bring heavy to moderate rainfall. 2. Tropical Depression This region is the centre of low pressure and characterised by closed isobars, which are small in size. The wind velocity at the centre is 40-50 km/hr. It is usually influenced by summer weather of India and Australia. Sometimes, it becomes strong and give heavy rainfall, after resulting in floods. 3. Tropical Storm Tropical storm is related with low pressure centre, closed isobars which rushes towards the centre with the velocity ranging between 40 to 120 km/hr. It developes over Caribbean sea, near Philippines and Bay of Bengal causing devastation of lives and properties. 4. Hurricane or Typhoon It is a form of massive tropical cyclone surrounded by several closed isobars. It moves with an average speed of 120 km/ hr. Hurricane has more symmetrical and circular isobar. The pressure increases sharply from centre towards the outer margin, resulting in presure gradient. Heavy downpour occurs, which is often uniformly distributed over a larger area as compared to other types of tropical cyclones. Tropical Cyclones are known by different names : Hurricanes – Carbbean and Pacific coast of Mexico. Typhoons – Sea of China and Japan Cyclones – India / Australia Willy-Willies – North Australia Tornado – South and Eastern USA. Bagguio – Philippines Comparison between Temperature and Tropical cyclones. Tropical Cyclone Extra-tropical cyclone The tropical cyclone have a thermal origin, exclusively over the tropical seas. Formed in middle or high latitudes, due to the development of front (35°-65° N and S) The size of the tropical cyclone is 1/3 of temperate cyclone It is much extensive size. Strongest winds of tropical cyclones take place at surface. Strongest winds of mid-latitude cyclones are higher up in atmosphere. It is associated with single eye There is more than one place where wind and rain is active. Wind velocity is very high It is low in comparison to tropical cyclone. Its relation with upper level air is not clear It has a distinct relation with upper level of air. Anticyclones The air mass in which pressure is high at the centre but decreases outwards is anti-cyclone. Winds move in a clockwise out-spiral in the northern hemisphre but in an anticlockwise out-spiral in the southern hemisphere. • They have a circular shape usually but at times assume V shape. • They are larger in size than temperate cyclone. 75 times the size of temperate cyclone. • It has the average velocity of 30-50 km/hour. • The high pressure at the centre causes the wind to move outward. • The wind descend from above at the centre and thus weather becomes clear and rainless. • It has no fronts.
It is the amount of water vapour present in the air at a particular period of time and place. Humidity of a place can be expressed in three ways: Absolute Humidity The measure of water vapour content of the atmosphere which may be expressed as the actual quantity of water vapour present in a given volume of air is called absolute humidity. This is measured as gms per cubic meter air. Absolute humidity changes with place and time. The capacity of air to hold water vapour depends on temperature. Warm air holds more moisture than cold air. Specific Humidity Another way to express humidity as the mass of water vapour per unit weight of air or the proportion of the mass of water vapour to the total mass of air is called the specific humidity. Specific humidity is not affected by changes in pressure or temperature. Relative Humidity This is a ratio expressed between actual quantity of water vapour present in the air at a given temperature absolute humidity and the maximum quantity of water vapour that the atmosphere can hold at that temperature. Relative humidity determines the amount and rate of evaporation. • Hygrometer is the instrument used for measuring relative humidity. It comprises of wet and dry bulb thermometer. Relative humidity Absolute humidity Humidity capacity = ×100 • Temperature and evaporation are directly proportional to humidity. • The process of transformation of liquid into gaseous form is called as evaporation. • Oceanic and coastal regions record higher humidity capacity of air than the remote continental regions. • Humidity capacity decreases from equator to polewards as the temperature also decreases. • The air having moisture content equal to its humidity capacity is called as saturated air. It balances the energy flow of the earth in the form of clouds. The process of evaporation and condensation are major means by which transfer of energy takes place from earth to atmosphere, which is the basis of precipitation. PRECIPITATION Condensation of atmospheric water vapour that falls under the gravity is called as precipitation. This could be in the form of rain, snow or hail etc. Its form depend on the temperature at which water vapour condenses. Forms of Precipitation Hail It is a form of solid precipitation consisting of large pellets or spheres of ice balls with the diameter varing between 5 to 50 mm. The falling of hail on the ground surface is called hailstorm. It is destructive as it destroys agricultural crops and claim human and animal lives. Snowfall It is the fall of large snowflakes from clouds on the ground surface. The dew point should be below freezing point for receiving snowfall. It is a result of sublimation. Sleet It is a mixture of snow and rain. It is a small pellets formed by freezing of raindrops or melting snowflakes. Rainfall It is the most common form of precipitation. It is a process wherein warm air ascends, saturates and condenses. Adiabatic cooling takes place when the relative humidity becomes 100 per cent. The condensation of water vapour takes place where large hygroscopic nuclei (salt and dust) is formed. Such droplets are called as cloud droplets shade. Rainfall occurs when cloud droplets change to raindrops which involves two processes: 1. The warm and moist air ascends to such a height that the process of condensation beings below freezing point. Both the waterdroplets and ice droplets are formed. The condensation takes place as the water droplets evaporates around ice droplets due to difference in vapour pressure. These ice droplets become large and fall when finally they are not able to be held back in the condensed icedroplets. 2. The suspended cloud droplets in the cloud are of varrying sizes. They collide among themselves at different rate as their size varies. They combine to form a large droplet. In this process several cloud droplets are coalesced to form raindrops. When these cloud droplets are large enough that they are unable to hold by ascending air they being to fall. Types of Rainfall Rainfall can be classified into three types: 1. Convectional Rainfall 2. Orographic Rainfall 3. Cyclonic or Frontal Rainfall 1. Convectional Rainfall The thermal heating of the ground surface through the process of insolation leads to rise of air as they become warm and light. The process of convectional rainfall mainly depends on two factors. (i) The supply of moisture through evaporation should be abundant so that its relative humidity becomes high. (ii) There should be intense heating through insolation process. The process of convectional rainfall involves intense heating of ground surface though solar radiation. As the warm air rises, the vacant shape is filled by surrounding air which too warm up when come in contact with already warm air. Ascending warm and moist air cools according to dry adiabatic lapse rate (10°C per 1000 metres) increasing the relative humidity. The moist air becomes saturated soon (relative humidity becomes 100 percent) and futher rising of saturated air causes condensation and cloud formation cumulo-nimbus clouds. The air further rises and cools with moist adiabatic lapse rate
(5°C per 1000 metre). When the air reaches the temperature of its surrounding cumulo-nimbus cloud is formed and there is instantaneous heavy rainfall. • It occurs daily in afternoon in the equatorial regions. • It is for short duration but point down heavily. • Occurs through thick dark and extensive cumulo-nimbus clouds. • It is accompanied by number of thunder and lightning. Convectional Rainfall Warm ascending air Ground Surface Cloud 2. Orographic Rainfall When the warm and moist air is obstructed by any hill or mountain, it starts ascending along the slope of the hill or mountain and get saturated after reaching a height. As a result condenses around hygroscopic nuclei. The presence of hill or mountain triggers the process of ascending of moist air, becoming cool and unstable. The slope of the mountain facing the wind is called as windward side and the other side of that mountain is known as Leeward side. Windward side receives maximum rain and leeward side receives no or little rain. The leeward side is also known as rainshadow region. This type of rainfall is called as orographic rainfall. • The mountain should be acting as a barrier across the wind direction. • Mountain or hill should be running parallel to the coast. • The height of the mountain too determines • Orographic rainfall Windward side Leeward side the amount of orographic rainfall. 3. Cyclone or Frontal Rainfall Cyclonic or frontal rainfall occurs due to ascending of moist air and adiabatic cooling caused by convergence of two extensive air mass. CLOUDS They are mass of very fine water droplets, ice particles or mixture suspended in the atmosphere. Clouds are formed by the adiabatic cooling of air when it is below its dew point. Cooling process is created by upward movement of light and warm moist air which reduces pressure, expands and reaches its dew point. There is further cooling below dew point causing condensation. Adiabatic process involves change in temperature of an ascending or descending air. The air which ascends (due to expansion of volume) results in cooling of air, whereas the air which descends results in warming a air at the rate of 10°C per 1000 meters. This rate of shade change is called as adiabatic lapse rate. 10° per 1000 meters change is only before dew point (condensation level) and after dew point is achieved the rate of change in 5°C per 1000 m. Types of Cloud Usually clouds are classified in terms of their vertical arrangement in the atmosphere of high, middle and low clouds. 1. High clouds: 6000 to 12000 meters above sea level. l Cirrus : Wispy, fibrous-looking cloud which indicate fair weather. l Cirrocumulus : A thin cloud, often globular and rippled. l Cirrostratus : Thin white sheet type which gives the sun and moon their haloes. 2. Medium clouds : 2000 to 6000 meter above sea level. l Altocumulus : Globular, bumpy looking clouds with a flat base covering entire sky.. l Altostratus : greyish, watery looking and a wool pack cloud.. 3. Low clouds: below 2000 meters above sea level. l Stratocumulus : Low rolling, bumpy clouds. l Nimbostratus : Fog-like low cloud causes dull weather with drizzle. It is also associated with lightning thunder and hailstorm. l Stratus : These clouds are low, grey and layered, almost fog-like in appearance, bring dull weather and often accompanied by drizzle air or snowfall. 4. Clouds of great Vertical extent: 1500 to 9000 m. l Cumulus : A round-topped and flat based cloud, which form a whitish grey globular mass. It some times becomes thunder cloud. l Cumulonimbus: Cumulus cloud which reaches up to 9000 meters, often indicates convectional rain, lightning and thunder storm. Distribution of precipitation across different regions of world. 1. Regions of Heavy Precipitation: Rainfall more than 150 cm per year are: (i) Equatorial regions: Amazon and Congo Basins, Malaysia, Indonesia and New Guinea.
(ii) Tropical Monsoon regions: Parts of India, South- east Asia and South China. (iii) Mid-latitude West Margin regions: Coastal regions of British Columbia, North-west Europe, South Chile and South Island of New Zealand. 2. Moderate rainfall (100 to 150 cm per year) (i) Eastern margins of continents in the trade-wind belt e.g. eastern margin of China, U.S.A., Brazil, South Africa and Australia. 3. Regions of very low rainfall (less than 25 cm.) (i) Tropical deserts – Western margins of continents in the trade wind belt, Californian desert (USA), Atacama (South America), Kalahari (Southern Africa), Sahara, Arabian Desert and West Australian desert. (ii) Mid-latitude desert – Interiors of large continents like Asia and North America. (iii) Polar Regions – Arctic and Antarctic. WORLD CLIMATIC ZONES 1. Equatorial Climate or Tropical Rain Forest Climate Location • It is found between 5°N to 10°N and S of equator. • The equatorial climate is found in the following 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. Climate • 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 is less than 5°C. • This region has no dry season. Average annual rainfall is 200 cm to 250 cm. The driest mouth in this region receives 6 cm of rainfall. • 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 year round rain produce most luxuriant vegetation in the region which are tropical rainforest or Selvas in South America. 2. Savanna or Sudan type of climate Location 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. Climate • This zone has distinct wet and dry season. • The mean temperature varies between 24°C to 27°C. • Annual precipitation of 100 cm to 150 cm is received From December to February there is no rainfall at all. • 80% to 90% of the rain occurs in rainy season only. Vegetation • 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 grow along the banks of the streams, are of broad-leaf and umbrella shaped. • Fauna: Elephants, giraffe, zebra, rhinoceros along with varieties of carnivores animals (lion, leopards, tiger, cheeta, hyena etc.) are found. 3. Hot Desert Climate Location 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 hemisphere. • 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 • Climate is dominated by subsidence of air masses and sub tropical anti cyclones. • Average summer temperature is between 30°C to 35°C. Mid-day temperature is recorded to be 40°C. • Daily range of temperature is great varrying between 22°C to 28°C • Annual range of temperature varies between 17°C to 22 °C. • These areas are nearly rainless or receive lowest annual rainfall (Less than 12). Vegetation • Normal vegetation is cactus, thorny plants, shrubs and herbs.
4. Steppe (Temperate continental) Climate Underline Location 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. Prairies (North America), Pampas (South America), Velds (South Africa), Canterbury (Newzeland), Downs (Australia) and Steppes (Russia). Climate • 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. Temperature in summer varies from 18°C to 24°C and in winter from – 4°C to 2°C. Such range of temperature is large. Rain fall occurs in spring and early summer and varies between 25 cm. and 75 cm. Rain is of convectional type and light. Vegetation Short grass grows everywhere. Trees are found only on mountain slopes. 5. Mediterranean Climate Location • The zone lies between 30°-40°N and S 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, Tunissia and libya) alongwith southern California coast. • In the southern hemisphere central chile, Cape town area of South America, South and Southwest coast of Australia. • Average winter temperature is 5°C to 10°C whereas that of summer it is 20°C to 27°C. • Mean annual range of temperature is recorded to be between 15°C to 17°C. • The zone experiences season shift of pressure belt • Winter rainfall is received through cyclonic storms. • More than 75° of the rainfall is in winter season. • The mean annual rainfall varies between 37 cm to 65 cm. • Summer winds are generally dry and hot. Vegetation • 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 growhere. • Citrus fruits are grown in this zone. 6. Sub-Tropical Humid Climate/ China type Location • It is found in the eastern boundary of the continent between 25°C to 40° N and S 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. Climate • 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. • Rainfall varies between 75 cm to 150 cm • Rain decreases as we move inland from coast. • Tropical cyclone is found and results in rainfall. Even winter cyclones are found here as it is associated with Westerlies. Vegetation • Dense evergreen forests are found alongwith decidoous sparse forest and grassland. They have broad leaves. 7. West European type Climate Location • The zone lies between 40° and 65° latitude in both the hemisphere 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. Climate • Average temperature during summer ranges between 15°C to 21°C. • Polar front causes the development of temperate cyclone in this region under the influence of westerlies. • Annual range of temperature varies between 50 cm to 75 cm. Vegetation • Broad-leaf deciduous forest (oak, birch, walnut, maple, elm, chestnut, etc). • Needle-leaf (coniferous) forest like pine, fir etc are found. • Mixed forest is also found here. 8. Monsoon Climate Location Monsoon region includes the eastern margins of continents which lies between 5° to 30° N and S 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, North Australia.
Climate • 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. • On an average annual rainfall received in around 150 cm. Rainfall shows temporal variation. • 80% of the rainfall is received within 3 months (July, August and September). • Some parts of Indian sub-continent receives winter rainfall (Tamil Nadu and Andhra Pradesh) from north- east monsoons. • Monsoon rainfall is basically cyclonic in character. • 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. Other kinds of timber are sal, acacia and eucalyptus. 9. Taiga /Boreal/ Sub-Arctic Climate Location 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. Climate • Winters are very cold and severe lasting for 6 to 7 months . This region has Verkhoyansk the “cold pole” colder than the arctic region. Summers are short lasting for 3 or 4 months and days are long; at 60°N the sun shines for 18 hours. • Rainfall varies from 25 to 100 cm. There is more rainfall near the coast. • 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 • Vegetation in this climate type is softwood coniferous forests (Spruce, fir, pine). • Fauna like reindeer, deer, elk, moose and wild cat are found here. 10. Tundra Climate Location • The northern most parts of Asia, Europe and North America (include Alaska and Canadian Islands). Climate • Average annual temperature is – 12°C. • Long, bitterly cold and severe winter are experienced. • Summers are short but cool. • Precipitation is below 40 cm and as snowfall. Vegetation • 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. Isolines It represents the equal value on the map. • Isobar: A line representing points of equal atmospheric pressure. • Isobath: A line representing points of equal depths. • Isobathytherm: A line representing depth of water with equal temperature. • Isocheim: A line representing points of equal mean winter temperature. • Isochrone: A line representing points of equal time- distance from a point, such as the transportation time from a particular point.