Physical Geography Quizzes
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Chapter 1: INTRODUCTION TO GEOGRAPHY
Geography – it means “Study of the Earth”. It has two parts:
- Location of Industries.
Fundamentals of geography:
- They represent angular distance from center of the earth.
- Latitudes or “Parallels” are concentric circles.
- Largest latitude: Equator [0°]
- Tropic regions: From equator to 23.5° N “Tropic of Cancer” and 23.5°S “Tropic of Capricorn”. Heat surplus regions.
- Temperate regions: from 23.5°N to 66.5°N and 23.5°S to 66.5°S. Heat deficit regions.
- Differential heating is responsible for different pressure and planetary winds.
- The sun is tilted on its axis by angle of 23.5°. This is the reason for the seasons. The variation in the length of day and night from seasons is also due to the tilt.
- The Earth completes a rotation around sun in 365 days. In March the hemispheres are equidistant from the sun this is spring.
- In June the northern hemisphere is closer to the sun so it’s summer in the north and winter in the south.
- The autumn is in September when again both hemispheres are equidistant. In December the southern hemisphere is closer to the sun and hence there is winter in the south and summer in north.
3. Longitudes / Meridians
- They are the angular distance of a place from the prime meridian [0°].
- 0° = Greenwich line, UK and 180° = international date line
- From International Date Line moving to east subtracts a day and moving west adds a day. Western hemisphere is one day behind and eastern hemisphere is one day ahead.
- Every country selects its standard meridian [for India – 82.5°]. India’s time is 5.5 hrs ahead of Greenwich meridian time.
E.g. If 12 pm at Greenwich then at 15° E its 1 pm and 15° W its 11 am. Since 15° is 1 hour.
Note: France has the highest 12.
- The Equator passes through: Ecuador, Colombia, Brazil, Congo, Uganda, Kenya, Somalia, Maldives, and Indonesia.
- Tropic of Capricorn: Chile, Argentina, Paraguay, Brazil, Botswana, Madagascar andAustralia.
- Tropic of Cancer: Mexico, Algeria, Niger, Libya, Egypt, Saudi Arabia, India, China, Oman, Bangladesh, Burma and Taiwan.
- GMT runes through United Kingdom, France, Spain, Algeria, Mali and Ghana in Africa
- IST runs through UP, MP, Orissa and Chhattisgarh
Chapter 2: EARTH
The upper layer of the Earth’s crust is called lithosphere. It has 2 parts – upper part is granitic rocks and forms the continents. Its main constituent is Silica and Aluminum and is also called SiAl. It has a density of 2.7. The lower part is denser and is called SiMa [Silica, iron, magnesium]. As the SiAl is lighter than SiMa the continents are said to be floating on denser SiMa. The thickness of the crust is about 30 miles.
Below the crust is the Mantle which is 1800 miles thick. It is made up of dense layer very rich in olivine. The interior of mantle is the core which has radius of 2100 miles. It is called NiFe layer as it is made up of Nickel and Ferrous/iron. The inner part of the core is solid.
The Earth has three layers:
- Outer layer: Continents [SiAl – Silica + Aluminum] are granite and oceans are basaltic
- Mantle and oceanic crust: SiMa; mantle is Olivine. Highly fluidic
- Inner layer: Core [NiFe – nickel + ferrous]. Outer core is liquid and inner core is solid.
Iron has highest composition in earth and oxygen has highest composition in Earth's crust. Continental crust is light and oceanic is heavy.
Rocks in the earth’s crust:
- Formed by solidification of magma or lava.
- Don’t have strata or layers.
- Don’t have fossils.
- They are non crystalline if volcano burst out and cools at the surface [e.g.: basalt] or crystalline if volcano doesn’t burst and cools inside surface [ e.g.: granite]
They are further divided into types based on mineral composition:
- Acid igneous rock: less dense and lighter
- Basic igneous rock: denser and darker
In terms of origin there are two main types of igneous rocks:
- Plutonic rocks: these are formed after the magma has cooled beneath the Earth’s surface. Because of slow cooling the crystals formed are large and easily recognized. E.g. granite
- Volcanic rocks: the molten rocks pour out of the surface as lava. This cools faster at the surface and crystals formed are small. E.g. basalt
- Most igneous rocks are hard and resistant and so are mostly used for road making, gravestones and monuments.
- Formed when sediments compact under pressure lose fluid and become solid called lithification. They are non crystalline.
- Have fossils and strata. E.g.: shale, clay, limestone, silica
- Mechanically formed sedimentary rocks: These rocks are made from accumulation of material from other rocks that is cemented together.
- Organically formed sedimentary rock: these are formed from remains of marine life having shells like oysters or snails. As the fleshy part perishes the calcareous part fuses together. Carbonaceous origin sedimentary rock is formed when vegetative matter is compressed into carbon forms due to weight of overlying matter. Peat, lignite and coal are formed in this manner.
- Chemically formed sedimentary rocks: these are formed from chemical precipitation from solutions. E.g. rock salt, gypsum
- Formed when agents like heat or pressure or both act on igneous or sedimentary rocks.
- No fossils or strata. E.g.: granite -> gneiss, sandstone -> quartzite
Weathering of Rocks:
The work of weathering is of two kinds: Chemical or Physical.
- Chemical: The reactions caused by elements in water or air causes the rocks to decompose slowly.
- Chemical Solution
- Wet climates promote chemical weathering and dry climate promotes physical weathering.
- Mineral composition of the rock and the density of joints and cracks also affect weathering.
- Decomposition by oxidation or organic acids.
- Physical weathering:
- Repeated cycles of high and low temperatures
- Repeated wetting and drying.
- Biotic factors like plant roots
- Activities of men like mining
Igneous rocks under lithification become sedimentary / [metamorphic under heat] and further on heat or pressure become metamorphic. This again on melting becomes magma which turns to igneous rocks.
Seismic wave studies: the waves are S waves [can travel through solids and gases] and P waves [can travel through all mediums but speed is fastest in solids and least in gases].
Formation of continents:
Theory 1: Continental drift theory
- Alfred Wegener propounded it
- It was based on matching coastlines, similarity in age of rocks, fossil evidence i.e. similar plant and animal fossil found on both sides of the continents and glacial evidence in tropical lands.
- His theory was that the super continent – Pangaea broke up into continents 200 million years ago by drifting over the oceans.
- However his theory doesn’t explain how the gravitational forces could have affected the movement of continents. He couldn’t explain the driving force for the drift. Also his model of crust doesn’t agree with modern version. The speed of drift suggested by him too was implausibly high.
Theory 2: Convention current theory / sea floor spreading:
- A convention cell which is like a conveyor belt moves under the crust and is responsible for drifting of the continents.
- The sea floor has a lot of diversity: Mid ocean ridges, trenches, continental slopes, ocean floor. Some questions emerged as finding proved that oceanic crust was 200 million years old, age of crust increases away from mid ocean ridge and sea mounts deformed at trenches.
- The sea floor spreads due to the convention current and magma comes out this forms new ocean crust and expansion of ocean crust.
- It could also explain trenches in the ocean. The diverging oceanic crust was heavier than the continental crust. It was subdued under and it melted inside the mantle.
Mariana trench: – Pacific Ocean near Philippines.
Diamantine trench: – Indian Ocean near Australia.
Theory 3: Plate tectonic theory
- Some questions that remained unanswered were the formation of Fold Mountains, reasons for earthquakes and reasons for Volcanism on land.
- The theory states that the crust isn’t continuous but broken into plates. The lithosphere floats over the Athenosphere.
- There are entirely continental, entirely oceanic and mixed plates. Totally 6 major and 20 minor plates.
- Plates interact due to earth’s rotation. These interactions are of types:
- Divergent plate boundary: below oceans the divergence of plates causes mid ocean ridges. And below continents it causes rift valley and nascent sea.
- Convergent plate boundary: ocean and ocean plate convergence causes island arcs like in the Indian ocean and Philippines archipelago; ocean continent plate convergence causes volcanic mountains like in Andes, rocky and atlas mountains and continent plate convergence causes fold mountains like Himalaya, alps and Ural.
- Transverse boundary: when the two plates slip past each other it doesn’t have any mountain formation but causes seismic activity. E.g.: San Andréa’s fault in USA.
Chapter 3: LANDFORMS ON THE EARTH
Landforms on the earth are:
Types of Landforms
They are of two types: Block Mountains and Fold mountains.
Mountain Building Process:
- Pull of descending limb of the convention current. The compressive force is exerted by the convention current.
- Geosynclines are elongated narrow depressions on continental margins. Here the sediments of marine origin are deposited by oceans and rivers.
- Because of the plate collision the geosynclines and continental plates are converged to form mountains. These give the mountains sediments of marine origin.
Types of Mountains:
Fold Mountains are also called true mountains and are the youngest mountains of the earth. They are formed due to compressive force of the plates. They can be either of continental – continental convergence origin or continental - oceanic convergence origin. Therefore only compression is the force that creates Fold Mountains.They are the most widespread and most important. These are associated with volcanic activity and mineral wealth. They are called mountains of elevation. The compressive forces push the layers of the earth upwards and these are formed into mountains.
Characteristics of Fold Mountains:
- Extensive mountain chain
- Great heights
- Formed along unstable part of the earth
- Sedimentary deposits of marine origin if formed from continent - continent convergence
These are formed due to forces within the interior of the earth. There are two reasons for formation. Firstly when there is tension between two blocks which causes them to move apart. Secondly when there is compression between two blocks which causes them to move closer and the central portion is elevated. The portion that is uplifted is called “Horst” i.e. Block mountain and the sinking part is “Grabben” i.e. Rift valley. E.g. Aravalli, Vindhyas and Satpuda are Block Mountains.
Characteristics of Block:
- Not true mountains.
- The differential erosion of horst gives it a look like a mountain range.
Volcanic mountains: These are formed when materials ejected from the earth’s crust erupts from the vent of the mountain. This material accumulates around the vent of the mountain. Therefore volcanic mountains are called mountains of accumulation.
Residual mountains: These are mountains formed from the effects of denudation agents like rivers, air, breeze etc.
This is raised land higher than surrounding areas. It is formed during mountain building process. It is raised land due to erosion of mountain from glaciers or deposition from winds or lava.
- Tectonic plateau: These are formed by earth movements that cause uplifts and are normally of considerable size and altitude. Intermount plateaus are plateaus enclosed by fold mountains. These plateaus are the most extensive and highest in the world. E.g: Tibetan plateau
- Volcanic plateau: Molten lava may issue from the Earth’s crust and spread over the Earth’s surface to form successive sheets of basaltic lava.
- Dissected plateau: These are formed from the action of glaciation and rivers on plateaux
These are flat areas with low heights. These are the most populated areas of the world. They are most fit for human habitation.
The depositional plains are formed due to rivers or sea. Erosion plains are formed due to erosions of plateau.
There may also be low hills that form a rolling topography.
- Structural plains: These are formed by horizontally bedded rocks. These make up some of the extensive lowlands of the world.
- Depositional plains: These are plains formed from depositional material brought by agents of weathering like rivers, glaciers etc. Running water is the single most potent agent of denudation.
- Erosional plains: These are plains formed from the action of agents of erosion like rain, rivers, ice and wind.
Lava and Volcanic Activity:
The main types of lava are:
- Basic lavas: These are hottest lavas and highly fluidic. They are rich in iron, magneisum but poor in silica. They flow fast and without explosions and so cover more areas. The resultant volcano is flat dome or shield.
- Acid lava: These are highly viscous and flow less fast. They also explode loudly.
- Shield volcanoes: highly fluid, gentle rising slopes and broad, flattened tops.
- Cinder cones: less fluid lava with large craters and steep slopes.
- Composite cones: highest and most common type.
In some volcanoes the top of the cone collapses into the vent or is blown off. This orifice gets widened forming a caldera. Sometimes a lake may form in this depression and is called a Caldera lake.
The greatest concentration of volcanoes is along the Cir-cum Pacific region which is also known as the “Pacific Ring of Fire” which has 2/3rds of the world’s volcanoes. It is also the region that sees the highest concentration of earthquakes as nearly 70% of the earthquakes are seen in this region.
Famous river plains in the world:
- Yangtze river plain:
- Third longest river in the world.
- Iron and steel industries / Coal industries located on the coast.
- Used as an inland waterway.
- Tigris and Euphrates river plain:
- Originates in turkey and flows through Syria and Iraq.
- Amazon basin
- Second longest river in the world.
- Large mineral reserves and oil reserves.
- Mississippi basin, USA
- Temperate grasslands and mineral reserves.
- Granaries of the world – Prairies.
- Murray – Darling basin, Australia
- Temperate grasslands – Downs
- Animal husbandry and mineral reserves.
Most of the lakes in the world are fresh water lakes and a few that have limited source of water and face high evaporation are salt water lakes. Lakes are however only temporary land-forms and shall be erased due to siltation and evaporation.
Factors responsible for lake formation:
1.Lakes formed due to Earth movements:
- Tectonic lakes: These are formed due to movements in the Earth’s crust. E.g.: Lake Titicaca which is the highest lake and Caspian Sea which is the largest lake.
- Rift valley lakes: These lakes are formed due to sinking of land between two parallel faults. E.g.: Lank Tanganyika the World’s deepest lake and Dead sea , the World’s lowest lake.
2. Lakes formed by glaciation:
- Cirque lakes: A glacier on its way down the valley leaves behind circular hollow in the heads of the valleys up in the mountains which become lakes.
- Kettle lakes: These are depression in the outwash plain left by the melting of masses of stagnant ice.
- Rock hollow lakes: Formed by valley glaciers that scoop out hollows in the surface. E.g.: Finland has 35000 such lakes and is called Land of Lakes.
3.Lakes formed by Volcanic activity:
- Crater or Caldera lake: When the top of the cone is blown off during volcanic explosion a crater or caldera is formed in which a lake may be created.
- Lava blocked lake: A stream of lava may flow across a valley and block a river thus damming it and creating a lake.
4. Lake due to subsidence of a volcanic lava surface:
- The crust of a hollow lava flow may collapse leaving a wide and shallow depression where a lake may form.
- Apart from these there are also lakes formed by erosion or deposition or formed from activities of man, animals and ornamental lakes.
- Tourist industry has become the National occupation in Switzerland due to the presence of lakes in the Alps.
Chapter 4: NATURAL CATASTROPHIC EVENTS
The major types of natural calamities are
Volcanism and causes of volcanism aren’t random. The areas of high volcanic activity are of ocean - ocean convergence and ocean continent convergence.
One of the regions is the Pacific ring of fire located in the pacific ocean and consists of border areas of China, Philippines, Japan, rocky mountains, Mexico , Andes mountains, Indonesia, new Zealand, Tanzania.
The second reason for volcanoes is the ocean - ocean divergence which creates peaceful basaltic eruptions as mid ocean ridges are formed.
The third reason for volcanic eruptions is breaking up of plates into blocks. The andesiticeruptions are seen in this type.
Intrusive land - forms:
- Sills - Horizontal
- Dykes - vertical
- Laccoliths – magma which couldn’t come out
- Balolith – intrusive granite rock
- Phacolith – shaped like waves
- Lopolith – saucer shaped.
Lava plateau: The cracks in the continental crust leads to basaltic flows which spread across land creating lava plateau. E.g. Deccan plateau.
Shield / Dome volcano: The magma reservoir creates volcanic islands. These create peaceful basaltic flow with gentle flow. E.g.: Hawaii.
Cinder cones: The ocean continent plates collide and then viscous lava explodes violently.
Composite cones: Volcanic eruptions led to new layers of ash or lava.
Fountains of hot water. Ground water heated by shallow source of magma. They have chambers in interior and water comes out like fountains due to pressure. Silica is dissolved in water.
Springs: The groundwater stored in rocks comes out of outlets called springs where the water table reaches the surface. The water may seep out gradually out of rocks or gush out as a fountain. Wells are man made for obtaining ground water by digging a hole in the ground till the water table is reached.
Water reaches interior and there it is heated. Water is heated by magma or hot rocks. It is common and is present in many places of the world. Cyano bacteria are present in this water.
Chapter 5: NATURAL CALAMITIES
Sudden movement or vibration in Earth crusts. It is due to release of energy and active internal dynamism of the earth.
- Shallow focus
- Intermediate focus
- Deep focus
Shallow focuses are the most destructive.
- Collision of plate boundaries like Ocean – Ocean, Ocean – Continental or Continent – Continent plates.
- Divergent plate boundaries lead to earthquakes due to formation of mid ocean ridge and eruptions.
- Transverse plate boundaries create friction of plates and lead to earthquakes.
- Breaking of plates and frequent interaction between them.
- Human induced due to Mining, building of dams.
- Re emergence of old fractures.
The tsunami waves are created due to the energy released from plate collision. The colliding energy is transmitted to the waves. These waves have greater wavelength and height when they hit the coast.
The vessels in the ocean don’t feel the tsunami. Waves also have higher speed.
Floods - Inundation of land. Indian climate where monsoon concentrated in a few months leads to flooding situation. The reasons of a flood are heavy rainfall, poor drainage due to topography, cloud burst, siltation of river bed, landslide in course of river.
Human induced reasons like deforestation, unplanned settlements, global warming and melting of glaciers and construction of dams.
- Afforestation on river banks
- Better settlement management
- Watershed management and rainwater
Rainfall is 60 - 75 cm then place is considered as drought affected. Southern part of Deccan plateau, Western Rajasthan and Ladakh are considered drought prone as these have 25% variability of normal rainfall.
In India drought is a more complex problem. Drought is due to inadequate development. It leads to agrarian poverty, high mortality of infants and mothers.
To resolve drought related problems:
- Improve agriculture irrigation facility
- Provide alternative livelihood
- Economic status of farmers.
Rain fed areas where agriculture completely depends on rainfall cover 55% of the country. 50% of food grains, 90% of pulses / millets and 66% of livestock population resides here. However, there is low productivity, high poverty and subsistence farming. 40% of India's B.P.L population live here.
The following are drought prone areas:
- Rain shadow region of western Ghats – don’t receive adequate rainfall
- Malwa, Bundelkhand, Mewar
- Eastern India – high rainfall but overuse and inadequate storage
- North east India – wettest part of India but no availability of storage.
- Agricultural income should be supplemented by alternate income sources too from animal husbandry, food processing, agro-forestry, handicrafts and tourism.
- For availability of alternate income 24*7 electricity, transportation, connectivity should be ensured.
- Mostly cash crops are grown in rain fed areas and this should be changed to less water intensive crops like millets. Agro practices should be changed like use of drip irrigation, sprinkler irrigation.
- Use of Drought-resistance variety, Conservation of soil moisture – mulching, Pre-monsoon ploughing and soil dressing ,Deep drilling of seed and fertilizers , crop-rotation.
Chapter 6: OCEANOGRAPHY
Ocean crust isn't uniform or flat. It has higher diversity than continental crust.
It is highly dense, thick crust and basaltic.
Oceanic crust is created at the mid ocean ridge and destroyed at the Trench.
The ocean floor is divided into three main regions:
- Ocean – Continent margin
- Continental shelf
- Continental slope
- Continental rise
- Deep ocean plains / Abyssal plains
- Mid ocean ridge
This is the seaward extension of the continent from the shoreline to the continental edge. They are absent on mountainous coasts and are widest in shores of lowland coasts. The continental shelf formation may be by submerging of continental edges due to rising water levels or by water erosion. Alternately they could have been formed by deposition of silt from rivers.
- They are responsible for preventing cold under current from rising and also increase the height of tides
- They are excellent location for ports.
The sunlight reaches the shelves and so minute plankton grows on them. This causes fishes to reach the shelves. The shelves are thus known as the richest fishing grounds of the world.
- It is shallow part of ocean and connected to the continent.
- It has highest bio diversity.
- Light reaches the bottom and hence aquatic plants are found.
- Depth is about 200m.
- Sediments from land are also found.
Resources in continental shelf:
- 90% of petroleum reserves are found in shelves. E.g.: Persian Gulf, Strait of Hormuz, Arctic Ocean, and Gulf of Mexico.
- Sulfur metal rarely found on land but is abundant in continental shelf due to marine volcanism.
- Concentration of heavy metals on shelf. E.g.: Monazite sand [thorium], gold, silver and diamonds.
Massive slope at the end of the shelf.
Landfalls of terrestrial deposits.
Great rivers form canyons, underwater waterfalls.
- Transition between ocean block and continental block.
- Absent near trenches as trenches consume the depositional material of the continental rise.
- Occupies 2/3rd of the ocean floor.
- High diversity in types of landforms and deposits from continental and aquatic sediments.
Ocean trenches: These are long, narrow deeps that penetrate to about 30000 feet at times. They are usually located near continents. Pacific Ocean has the deepest trenches.
Resources from an abyssal plain:
- Poly metallic nodules are a concentration of metals around a core. Found in all oceans. Some of the minerals are rare on land.
UN Convention on laws of seas:
- Decides deep sea mining, environment protection, maritime boundary and dispute settlement.
- As per the convention, territorial sea is 12 miles from coast, 24 miles is contiguous zone and 200 miles is the exclusive economic zone where state can explore minerals and produce energy.
Chapter 7: ISLANDS
A piece of land surrounded by water on all sides. Generally formed of the following types:
- Continental islands: These islands were formally a part of the mainland and now detached from the continent by a shallow lagoon or a deep channel. The rise in sea levels then submerged the low lying areas that connected them. The evidence of this is the presence of identical flora and fauna on both sides of the land.
- Individual islands: These lie just outside the mainland very much associated with the characteristics of the mainland they were once a part of.
- Archipelagoes: Groups of islands varying in shapes and sizes.
- Island arcs: Islands form an archipelago in the shape of a loop around the mainland, marking the continuation of mountain ranges which can be traced on the continent.
- Oceanic islands: These are isolated islands that lay thousands of miles away from the mainland. They have flora and fauna different from the nearest mainland. They are usually sparsely populated but are useful stops for the aeroplanes and steamers.
- Volcanic islands: Many islands are actually topmost part of cones of volcanic mountains that rise from the ocean bed.
- Coral islands: These are lower and emerge just above the water surface. These are built by coral animals of various species and are found near the shores of mainland and in midst of oceans.
- Sources of greatest biodiversity amongst marine ecosystems.
- They are indicative of the health of the marine ecology. Cant survive in muddied waters or polluted water. They need sediment free water.
- Primary food chain. Home to Zoantharia which is aquatic primary producer.
Characteristics of coral reefs:
- Corals are tiny fleshy sea anemones. They extract calcium from the sea and form skeletons to protect their bodies.
- Each generation dies on top of the previous.
- They have a symbiotic relationship with microscopic plant Zoantharia which are photosynthetic in origin.
- They corals provide protection to Zoantharia and Zoantharia provide food to the corals.
- When corals are in stress they expel Zoantharia and become white. Ultimately they die without food.
Conditions needed for coral reefs:
- Shallow platform where sunlight reaches.
- Temperature 25-27°
- Warm, tropical and low latitude waters.
- Salinity should be 33 ppm.
- Not at mouth of the river; they need circulating nutrient rich water.
Reasons for coral bleaching:
- Global warming and ozone depletion
- Ocean acidification,
- Algal bloom
- Marine pollution and oil spills.
Formation of coral reefs:
- Fringing reef: coral reef is formed bordering an island or continent. A distance is created between island and the reef. Here small water bodies are seen to form called lagoons.
- Barrier reef: reef isn’t continuous but broken. The lagoons can connect to ocean. Here the coral reef if formed parallel to the coast it’s called barrier reef.
- Atoll: the hill is submerged and now only narrow ring of reef is visible.
Theory of Reef Formation
Formation of reefs: Subsidence Theory by Darwin
All reefs started as fringing reefs of islands or top of volcanoes that emerge out of sea bed. Then these islands subside with Earth movements.
However the fringing reefs continue to grow upwards. The corals also continue to grow outwards as more favorable conditions are seen there then at the inner edge.
Finally a barrier reef is formed and this becomes an atoll as the inner island is completely submerged due to the down warping.
Glacial Control theory: RA Daly
He said that a close relationship exists between the Glaciation and Coral reef formation. The theory states that the Ice Ages saw a great marine erosion due to absence of coral barriers. The erosion lowered the islands.
Then as the glaciers melted the water levels rose. The coral activity started and now the island was covered by corals. However, as the island submerged due to erosion and wave action, the corals continued to move upward to rise above the water level. This created Atolls.
Chapter 8: MOTION OF OCEANIC WATER
Wind pushes the water body. Then gravity pushes the crest downwards and falling water pulls the troughs upwards. Actual motion of water below the surface is circular.
They are shallow and narrow stream of water circulating along the ocean margins. They circumnavigate the world.
The currents are created due to
- Winds – Most currents follow the winds.
- Coriolis force- the earth’s rotation deflects the ocean currents to east in north and south.
- Insolation – water at equator is heated and rises. The water at poles cools and sinks, this water flows towards the equator at subsurface level to maintain the loss.
- Also insolation increases salinity and the high saline water sinks and less saline water rises to the surface. The equator water is less saline [heavy rainfall] and moves to polar high saline water [icebergs].
- Gravity and coastlines.
The best fishing grounds in the world are places where hot and cold current meet like Japan and east coast of America but are foggy areas making it tough for fishing.
The cold currents are also responsible for desiccating effect on the deserts.
The winter current in Arabian Sea caused movement of water towards Arabia and in summer caused movement of water towards India, Thus facilitating trade.
- When wind blows in the north direction it creates a flow of water in the western direction. This west flowing water then leads to the divergence at the coast and draws water from below the surface to the top. This is “Upwelling”.
- The cool and nutrient rich water from below comes to the surface. This causes reproduction of phytoplankton and zooplankton.
- When the wind moves southward it causes flow of water towards the coast and this createsdown welling.
- Due to the gravitational pull of the sun and the moon causes tides.
- The tides depend on depth of ocean, configuration of coastline and openness and closeness of sea.
- The perigee tides [moon is closer] are higher than apogee tides.
- When sun, moon and earth are in a line either during full moon and new moon we get spring tide which is the highest high tide and neap tide is when sun, moon and earth are at right angles and this is lowest high tide.
- In spring tide low tide is lower than usual and in neap tide the low tide is higher than usual.
- Tides help large ships enter and leave ports. E.g. Kandla and diamond harbor are tidal ports.
Vishakapatnam is deepest landlocked port, Chennai oldest artificial port, Kolkata is oldest port.
Estuary: mouth of a river is submerged or low lying under sea water. The river deposit create long narrow delta like Narmada and Tapti.
Temperature of ocean water:
The process of insolation is responsible for ocean temperature. The average temperature of ocean is 3-5°. But the average temperature of surface of ocean is 25°.
It is highest at the tropics not the equator as equator has high cloud cover and rainfall. It decreases towards the poles. For same reason the diurnal temperature range of tropics is higher than equator.
Due to large land mass in the northern hemisphere the temperature of water is higher than in south.
The enclosed seas of tropics are warmer than open oceans. The enclosed seas of temperate are cooler than Open Ocean.
Upwelling brings cold water on top but down welling piles warm water on top.
Bigger the size of the ocean better mixing of water and so less annual range of temperature.
Temperature decreases with depth. The decrease rate is higher at equator than the poles.
Salinity of oceans
Sodium chloride is the highest percentage present in ocean. Both sodium and chlorine have high residual time and hence remain in highest proportion.
The proportion of salt remains same in all parts of the ocean.
Salinity decreases from equator to poles but highest salinity is in tropics as equator gets high rainfall and low evaporation due to cloud cover.
Variations in salinity:
- Salinity increases with high evaporation rate, windy conditions, no fresh water source and down welling.
- Salinity decreases due to high rainfall, low evaporation rate, upwelling and melting of glaciers.
Chapter 9: CLIMATOLOGY
During early life of the earth there was abundance of hydrogen and helium. Extensive volcanism increased nitrogen, sulfur, water vapor, argon and carbon dioxide. Then heavy rains pushed the bulk of CO2 into the oceans. Currently the proportion of gases in the atmosphere is
Nitrogen – 78%
Oxygen – 21%
Argon – 0.93%
Carbon dioxide – 0.03%
Layers of the Atmosphere:
The atmosphere extends up to 10000 km above the earth’s surface. The parts of the atmosphere are:
- 90% of atmosphere within 32 km. Tropopause is at 8 km at poles and 18km at equator. At equator cumulonimbus clouds are formed.
Climatic elements like temperature, pressure, humidity, precipitation, clouds lead to variations in local climate and weather phenomenon. The variable water content in the atmosphere leads to great contrast in weather and climate. Without water in the atmosphere there would be no weather or climate
- Temperature decreases with height. It is transparent to shortwave radiation but G.H.G's absorb long wave terrestrial radiation.
- Weather phenomenon is formed at troposphere.
- Temperature increases with height. Ozone layer is present here and UV radiation is absorbed.
- Stratosphere lies above the troposphere and has no dust, smoke or water vapor however seasonal temperature variations are seen.
- Polar stratospheric clouds present. Spy planes, commercial planes and weather balloons fly here.
- No GHG's and temperature decreases with height. Noctilucent clouds seen.
- Meteors burn in this layer.
Thermosphere - Ionosphere
- Gases in ionic state trap insolation. Temperature increases with height.
- Ionosphere layer makes short wave radio transmission possible over long distances.
- Largest layer of atmosphere. Useful in radio communication.
- Reflects low frequency and high frequency waves but not very high or ultra high.
Sun’s energy reaches as solar or radiant energy by process called Insolation. Out of this 35% is reflected back by the dust and the atmosphere, 14% is absorbed by the water vapor in atmosphere and is scattered by dust particles in air this causes “Blue Sky phenomenon”.
The remaining 51% is absorbed by earth’s surface and heats it. The surface the through conduction and convection heats the air above it. Radiation of heat at night by the surface continues during night and since insolation is absent the surface cools.
Land is heated rapidly than water as the heat in water is spread out evenly due to the motion of water. The opaque nature of land means that more heat is absorbed and so land is heated and cooled faster. Transparent nature of water also leads to less heat being absorbed. Specific heat of water is higher so it takes longer to heat. Interiors of continents also face higher temperature variations than coastal areas as the moderating influence of the sea is not seen there.
The differential heating gives rise to land and sea breezes. During day as land gets heated faster than water the air above it is warmer and less dense. The sea remains cool and so a high pressure belt is formed and we experience sea breeze. This is usually stronger in tropics than temperate regions. During night, the land is cooled faster than sea and so a low pressure belt is seen over sea. Winds now move from land to sea and we get land breeze.
Slopes to are affected by temperature as a steep slope is heated faster than gentle slope. Mountains having east west alignment also see their south facing ‘sunny slope’ have a higher temperature than their north facing ‘sheltered slope’. The southern slopes thus see more cultivations and settlements.
Dry soils heat and cool faster than wet soils. The darker soils also better absorbers of heat than lighter soils. The leaves of trees in jungles loose water during day due to evapo-transpiration and this makes the air cooler. The relative humidity increases and mist and fog may form.
Albedo is the percentage of solar radiation reflected by the surface of the solar radiation that is incident. Lower albedo is for dark soil and higher albedo is snowfall.
Movement of Air:
Air moves from high pressure area to low pressure area [advection]. When air gets warm it expands as it becomes lighter [convection].
When air is heated it goes up. If it has moisture it condenses and brings rain. However this causes instability. Similarly when air cools it can’t rise it sinks causing high pressure conditions or anti cyclonic conditions on ground.
In hill areas a hot day followed by a cloudless night see the air at a higher altitude cool much faster. This cold, dense air sinks downwards and pushes the warmer air to rise. The temperature at the bottom of the valley is lower than the top. This is called “temperature inversion”. Normally temperature decreases with height but when it increases.
Case 1: On a cool night the air above cools rapidly than the air below. The warm air rises upwards than the colder air. This causes temperature inversion.
Case 2: In a valley the cool air descends downwards and the warm air rises. This cool air causes frost and damages crops.
Effects of temperature inversion:
- Fog - The water droplets condensed around a dust particle. It reduces visibility and damages crops.
- Atmospheric Stability – discourages rainfall.
Smog is when water droplet condenses around a pollutant like SO2. It too reduces visibility and is a health hazard. It occurs in cool humid climate.
Photochemical smog: it occurs in warm, dry and sunny climate. It is due to unsaturated hydrocarbons and ozone in presence on sunlight. It is oxidizing smog.
Chapter 10: TYPES OF CLOUDS
Types of clouds:
- Cirrus: indicate fair weather and good sunset. Look fibrous or wispy.
- Cirrocumulus: Appear like white globular mass.
- Cirrostratus: resemble thin white sheet or veil.
- Altocumulus: indicate fair weather.
- Altostratus; dense, grayish clouds
- Stratocumulus: rough, bumpy cloud
- Stratus: Brings dull weather with light drizzle.
- Nimbostratus: Rain clouds. It also brings snow or sleet.
4.Clouds with great vertical height:
- Cumulus: Typically seen in tropical, humid regions.
- Cumulonimbus: Thunder cloud brings rain with thunder and lightning.
Phenomenon caused by High Humidity
Haze: It is caused by smoke or dust in industrial areas or when there is unequal refraction of light in air of different densities in lower atmosphere. This is seen in regions of low humidity [Relative humidity < 75%].
Mist: It occurs in areas of high humidity where relative humidity is 75% +. Condensation of water vapor in air causes small water droplets to float about in lower atmosphere forming clouds.
Fog: These are formed when water vapors condense on smoke or dust particles. A dense ground cloud is formed reducing visibility. Although fogs are seen in tropics and temperate areas, they are denser in high and middle latitudes than tropics. Fogs are more common over seas than land and prevalent in coastal areas.
Haze and Mist occur more commonly in dry interiors.
Clouds and their types
Low altitude clouds:
- Nimbostratus – rain bearing
- Stratocumulus and cumulus are fair weather clouds.
Middle altitude clouds:
High altitude clouds:
- Cirrostratus, cirrocumulus and cirrus.
Clouds with vertical development are cumulonimbus which is stormy clouds and an indicator of cyclonic heavy rainfall.
Rainfall and its types
The term "rainfall" is used to describe precipitation in the form of water drops of sizes larger than 0.5 mm. Other forms are snow, drizzle, glaze, sleet and hail.
Types of rainfall:
- Frontal and cyclonic - Seen in temperate regions and is reason for rainfall during winters there. Warm air rises over cool air and is cooled due to it. this leads to condensation and rain.
- Convectional - Hot air formed due to sun's heating effect on oceans rises upwards and condenses. This rain is seen in equatorial and tropics.
- Orographic - This is seen where moist air is forced to climb a mountain barrier. The windward sides of mountains see this rainfall. It is also called “Relief rain”. The leeward side of mountain however doesn’t receive much rainfall and are called “Rain shadow regions”. E.g: Western ghats
Pressure systems of the world:
Entire earth is divided into four pressure belts. Belts aren’t continuous but pockets of low or high pressure. Low pressure is created by heat and rising movement of air. High pressure is created by low temperature and descending air.
The belts are:
- Equatorial low pressure belt.
- Sub tropical high pressure belt
- Sub polar low pressure belt
- Polar high pressure belt.
Equatorial low pressure belt OR inter tropical convergence zone:
The direct insolation leads to low pressure as the air is heated. The heated air rises upwards and condenses to bring evening rain.: The region along the equator and within 5 degree North and South is the equatorial low pressure belt is called Doldrums.
This convectional rain is common throughout the year in equatorial areas.
Calm belt with slow winds.
Sub tropical high pressure belt:
The air above the equator moves towards the poles but due to Coriolis force it is deflected and its path increases. The air loses energy and cools down; it descends and creates a high pressure belt.
Sub polar low pressure belt:
The cold air from the poles moves to the equator but the warm air of the sub tropic high pressure zone collides with it. The warm air rises here and creates a low pressure zone. About 30 degree North and South is the area of descending air currents or wind divergence or anticyclones. These are the horse latitudes. 60 degree North and South are the temperate low pressure belts and zones of cyclonic activity. Then at 90 degree north and south are the polar high pressure belts.
Polar high pressure belt:
The air from the low pressure sub polar belt descends here creating high pressure. Also the low temperature cools air.
These winds blow in the same direction throughout the year. But due to Coriolis force their direction is deflected. Winds tend to blow from high pressure belts to low pressure but due to Earth’s rotation are deflected to right in north hemisphere and left in south hemisphere - “Ferrel’s law”. Coriolis force to is absent at the equator but increases towards the poles. Due to large expanse of oceans in the Southern hemisphere compared to North, planetary winds blow harder.
Trade winds or Easterlies:
They blow from sub tropical high to the equatorial low. They are deflected from east to west due to Coriolis force.
The trade winds blow from east to west. But they lose moisture as they pass over the continents. The western margins of the continents don’t receive rain. Hence deserts are formed called trade wind deserts.
The second reason for deserts is they are on contact with cold currents that reach the western margins of the desert. These cold currents create a desiccating effect on the trade winds.
They blow from sub tropic high pressure zone to sub polar low pressure zone. Their direction is from west to east due to Coriolis force. Due to absence of land mass in southern hemisphere they have high velocities.
Blow from Polar Regions to sub Polar Regions. Direction is east to west.
These are monsoon winds in Indian subcontinent. The easterlies blow from north to south in winter and south to north in summer over some areas only.
The reason is earth tilted axis which causes apparent movement of the sun in the north during June - July. This causes shifting of the low pressure belt or ITCZ to the north.
This brings rainfall to India.
Land and sea breezes:
During the morning the sea gets heated slower than land. The land remains under low pressure and sea is high pressure. Thus we get sea breeze. In the night the land cools faster than sea due to lower specific heat. This creates low pressure over sea and the high pressure over land. Hence we get land breeze.
The fishermen use this system to move from land to sea and back.
Upper troposphere winds:
The troposphere has a different situation than at land. Here there is high pressure over the equator and low over the poles. They blow from west to east “Westerlies”. In these winds there are strong, narrow band of winds called Jet Streams [speed – 300 kmph].
8-20° latitude. Movement from east to west. They are created due to thermal conditions. Their path is difficult to predict. They have winds of high speed but quickly dissipate on land. They mostly affect coastal areas.
Location: Bay of Bengal, western pacific i.e. Philippines etc and Gulf of Mexico when formed over these areas they make landfall hence the coastal parts of these areas are largely affected.
The other regions where they are formed but can’t make landfall are Arabian sea, east coast of Africa, west coast of Mexico and south west USA.
- The increase in the sea surface temperature causes air to warm and rise. This air also has moisture. The low pressure zone at sea level is where air converges.
- As air moves upwards the Coriolis force causes spiral movement. After reaching the top it dissipates.
- Continuous process of above causes a cyclone where a high pressure eye is surrounded by low pressure region. But as this cyclone is fueled by moisture when it makes landfall it dissipates quickly. This is due to being cut off from moisture.
30-40° latitude. Movement from west to east. They are formed due to movement of air [rising]. They have winds at 40-50 mph. They don’t dissipate quickly and cause destruction.
They are located on the western coast of USA and Europe. They are influenced by the Westerlies.
Chapter 11: WEATHER PHENOMENON
Weather v. Climate
- Weather changes frequently but Climate is the average atmospheric conditions of an area over a considerable time.
- Climate of temperate latitudes is far more variable than the tropics.
Points to remember about the Weather effect's
- Death rates of tropics are higher than deserts as germs find it difficult to transmit easily in dry conditions compared to humid conditions.
- Rainfall, snow, sleet, hail are types of precipitation and are measured by Rain gauge.
- Places with the same mean annual rainfall are joined by the lines called “Isohyet”.
- Mercury is used in the Barometer as it is the heaviest known liquid. The mercury column at sea level is 30 inches approx. or 1013 milli-bar / 760 mm of Hg [Mercury].
- Lines called isobars join regions of high pressure.
- The Temperate latitudes see higher variations in pressure which leads to cyclones and anti-cyclones. As one goes higher in altitude the pressure decreases. The drop is 1 inch for every 900 feet ascent in height.
- Aeroplanes use a modified barometer called Altimeter.
- Temperature decrease is 1 Fahrenheit drop for 300 feet ascent in altitude.
- Humidity is the measure of dampness in the atmosphere. It has two types:
- Absolute and Relative humidity. The Absolute humidity is the amount of water vapor in grams per cubic meter.
- Relative humidity is the amount of water vapor present in air at a particular temperature compared to the total amount of water vapor, air can hold at that temperature.
Relative humidity = 80%; This means Air holds 4/5th of the water vapor it can hold.
Important instruments related to Weather
- Wind director – Wind vane
- Wind speed – Anemometer
- Relative Humidity - Hygrometer
- Places with equal sunshine duration are joined by “Isohels”.
- “Isonephs” are lines that join places with equal degree of cloudiness.
Formation of thunderstorms:
Heavy rainfall with thunder and lightning. They usually last for short amount of time. Cumulonimbus clouds are formed. This leads to atmospheric instability and convectional rainfall.
- Air motion is upwards.
- The accumulation of water increases and water droplets descend the surrounding is cooled. This leads to more downward draft and spreads throughout the entire cumulonimbus.
Types of thunderstorms:
- Thermal thunderstorms – localized, intense heating of ground.
- Orographic thunderstorms – obstruction due to mountains leads to it as forcible vertical movement is needed.
- Cold front thunderstorms – hot and cold air collide to get this.
Occurs mostly in temperate regions where cold and warm air meets. South east of USA is called “Tornado Alley”.
Polar stratospheric clouds:
They are formed in winter and contain nitric acid, sulfuric acid and water. Nitric acid reacts with CFC to create chlorine. This creates a chlorine concentration in winter. This chlorine reacts with oxygen molecule of ozone and destroys the ozone layer.
Ozone depletion is more at southern pole and is called ozone hole - “Thinning of ozone layer in stratosphere below threshold” [not an actual hole].
El - Nino and La - Nina
There are oscillations in the pressure gradient and air circulation every 2-3 years in South Pacific Ocean. This is called El Nino Southern Oscillation.
The term "El Niño" refers to "the boy" / "Child christ" , so named because the pool of warm water in the annual weak warm ocean current that ran southwards along the coast of Peru and Equador around Christmas. "La Niña", the 'opposite' of El Niño, translates to "the girl".
During a normal year the following events are seen:
- The south equatorial current takes warm water to Australia and creates a low pressure region. This heats the air and it rises upwards. The resultant atmospheric instability leads to rainfall in Australia.
- The air that rises up cools and diverges. It comes to the South American coast. Due to this high pressure is created and has a desiccating effect on the Atacama Desert.
- This is High pressure and low pressure formation is called Walker Cells.
- The south equatorial current takes warm water to the west from east. This causes up-welling at Peru coast and rich fisheries at Peru.
During El Nino year:
- The south equatorial current weakens and water piling is reduced to Australia.
- The abnormal cooling of Australian region and warming of Peruvian coast is seen. The low pressure condition over Peru and high pressure over Australia causes drought. Reversing of walker cells is observed.
- This causes rainfall in Atacama Desert. The up-welling at Peru coast is affected and the fishery business goes down.
- El Niño causes droughts in India and Indonesia as well.
Chapter 12: CLIMATIC REGIONS OF THE WORLD
Between 5 and 10 ° North and South of the equator. The temperature is uniform throughout the year with no variations. Cloudiness and heavy precipitation make the climate bearable. The annual range of temperature is small and so is the diurnal range of temperature [ range of temperature in a 24 hour period]. Rainfall is heavy and throughout the year with no dry period. The equinoxes coincide with the periods of maximum rainfall [April and September].
- Morning is bright and sunny.
- Afternoon sees heavy convectional rainfall accompanied by lightning and thunder.
- Relative humidity is high and weather feels sticky.
- Equatorial vegetation has features like:
- Growing season throughout the year.
- Great variety of vegetation
- Trees are tall as they compete for sunlight. Undergrowth is less as sunlight may not reach the ground.
- Tropical and equatorial forests have large number of species in a small area and this makes commercial exploitation tough. Also the hardwood doesn’t float on water and is difficult to transport. Thus most of these nations are net importers of timber.
Oil palm, cocoa and rubber are the main crops.
Hot and wet climate throughout the year. Rainfall during evening and high biodiversity. Intense competition amongst species for survival. Large number of species in a small area which makes it tough for exploitation. Presence of many epiphytes.
Also the trees are hardwood and difficult for transportation by rivers. Hence most of these regions are importers of timber.
Living conditions are poor because of hot and moist climate. High incidents of disease. Death rates are higher in equatorial and tropical regions due to the pathogens finding it easier to spread in moist weather then the dry weather in deserts.
Deserts of the World
Deserts occupy 1/5th of the World’s land. They are almost always present in 15-30 degree parallel both north and south of the equator. They lie in the trade wind belt in the western margin of continents and hence receive offshore trade winds. They are also bathed by cold currents that have a desiccating effect on the moisture and hence it doesn’t precipitate.
Types of deserts:
- Trade wind deserts
- Continental interior desert / mid latitude desert – they have extreme temperatures.
- Rocky deserts
- Stony deserts
- Sandy deserts
- Mountains deserts
Landforms in the dessert are formed due to chemical actions of minerals present in rain water on the rocks [weathering], rapid heating and cooling of rocks due to high temperatures. Water is expanded on heating in the morning and contracts at nights due to low temperature. This also weathers the rocks. Wind effects are also high here as there is no presence of vegetation to block the winds.
They are present between 15-30 degree latitudes in western margin of continents. They receive offshore trade winds hence low precipitation. Also they are basked with cold currents which have a desiccating effect on the winds.
The deserts are present on leeward side or rain shadow side of mountains. Hence they experience low rainfall.
Low population and xerophytic vegetation. However compared to temperate deserts the annual temperature range is low. Deserts also have high diurnal temperature range i.e. day and night temperatures have high difference.
Desert plants have long roots and thorns in place of leaves to prevent evaporation. Cacti are plants that store water in the stems to withstand long droughts.
Nomadic herders like Bedoiuns [Sahara] and Bindibu [Aborigines of Australia] tribes are seen in deserts. Tuaregs and Gobi Mongols are nomadic horsemen who have settled here.
These are located in interior region. The rain bearing winds don’t reach here. They have high annual temperature range than tropical deserts..
Tropical Grasslands: Savannah
Transitional type of climate found between the hot trade wind deserts and the equatorial forests. There is a distinct cool, dry and hot, wet seasons here. In days the clear sky and the treeless land ensure that the temperatures are high and similarly the night time temperatures are low due to the radiation of heat from the land. Thus the high diurnal temperature range is a characteristic feature of the savannas.
Tall grass and short trees are the features of savanna forest. Trees are mainly deciduous origins. Wildlife is plenty. Masaai [nomadic, cattle herders] and Hausa [settled cultivators] are the tribes found there.
The Sudan climate is also responsible for rapid deterioration of soil fertility. The torrential rains cause heavy leaching of minerals like nitrates, potassium and phosphates. Then in the summer the high evaporation rates water of the soil dries up and so the savanna regions have laterite soils. These can’t have good yield unless proper fertilizer treatment is given.
Temperate grasslands: Steppe
These are practically treeless grasslands in the interiors of the continents. They are remotely located and are far away from the influence of any moisture bearing winds.
In Northern hemisphere these are the Steppes and the Prairies, in the Southern hemisphere they are Pampas, Velds and Downs. In the northern hemisphere , these grasslands face extreme heat in summer and extreme cold in winter.
This is due to being far away from the moderating influence of the sea. In Southern hemisphere, due to moderating influence by the oceans extreme temperature swings are absent. Rainfall is mild in north compared to south.
Wheat cultivation is the major occupation in the prairie grasslands. But due to the large landholdings one characteristic feature of the agriculture is poor yields. This is due to low attention that can be paid by a farmer compared to those who have small land holdings.
However due to sparse population majority of the wheat is exported and so the Prairies are called the Granaries of the World. 75% of Canadian wheat is exported to European nations that though have higher yield but can’t feed their dense populations.
Wheat has two types:
- Summer wheat: This is grown in parts where winter temperatures are too low and so seedlings are sown in summer. This wheat is used for making cakes, biscuits and pastries as it is too soft for bread making. 25% of wheat produced is of this type.
Winter wheat: 75% of wheat is of this type. It is sown in winter and dried in summer and so becomes hard. This is best for making breads.
Tropical Monsoon and Tropical Marine:
The basic cause of monsoon climate is the difference in the rate of heating and cooling of the land and sea. The summer sees intense heating of the tropic of cancer region which is the Tibetan plateau; the heating causes a zone of low pressure to develop there.
At the same time in southern hemisphere there is winter and a high pressure belt is formed around the Continent of Australia. The winds blow from high pressure to low pressure and they are attracted to the Indian subcontinent which they reach as the “Southwest Monsoon”.
The conditions are reversed and in the winter a high pressure zone develops in the Central Asian region. The winds blow from there to the low pressure belt in Australia created by intense heating as the sun is now over the Tropic of Capricorn. These winds arrive to Australia as the North west monsoon.
Thus, Tropical Monsoon climate is characterized by the seasonal reversal of winds.
Cool and Dry winter:
The high pressure belt over Central Asia leads to out blowing dry winds. These cause some cyclonic showers over North West belt of India. These winds then cross the Bay of Bengal and acquire some moisture. This moisture causes precipitation over the Southern tip of India which is the Andhra Pradesh, Tamil Nadu region.
Hot, dry summer:
This period sees intense heating of the Indian subcontinent and no precipitation is seen. This lasts from March to May.
Mid June to September:
This is the rainy season in the subcontinent and during this period almost all of the precipitation is seen. Heavy and concentrated rainfall is a characteristic feature of Tropical Monsoon climate.
Tropical Marine climate:
This occurs in the Eastern coast of Tropical countries. They receive rainfall from onshore trade winds continuously throughout the year. The pattern of rainfall is that a peak is seen during the summer which lasts for 4 months. However these regions are also affected by tropical cyclones, hurricanes and tycoons.
Tropical monsoon forests:
These are deciduous due to the presence of a dry period in the rainfall. Thus the leaves are shed. The monsoon forests are less thick and have far fewer species in an area compared to equatorial forests. This also means that they can be commercially exploited for timber. The tropical countries are major producers of timber for the world.
Agriculture is main occupation of most people and the main crops are rice [most characteristic crop of monsoon and marine regions], sugar cane [commercial cash crops], jute [grown mostly along the Ganga - Brahmaputra delta], tea, coffee.
Western margin of temperate areas: Mediterranean Climate
These are regions found in the western margins of continents between 30-45 degree North and South of the equator. Basic cause for this type of climate is the “Shifting of Wind Belts”.
In summer there is a dry, warm period. Due to the movement of the sun to the top of the tropic of cancer, a warm zone or low pressure region is built on the Mediterranean region and so rain bearing winds are not seen here. But offshore trade winds blow here which don’t bring much precipitation.
Wet winter is a characteristic feature of these regions. The precipitation is brought by the westerly which are onshore. The Wet Winters are a unique characteristic of this region. However this affects the grassland as a cold wet season isn’t favorable for growth of grass and it is thus wiry and bunchy and unsuitable for animal farming. Due to these reason cattle herding isn’t practiced here and Mediterranean regions are Net importers of Dairy products.
Citrus fruit cultivation is practiced here and this region is responsible for majority of the World’s exports. Olive trees can also grow here as it can survive long spells of dry seasons due to its long and deep roots. Since animal fats are scarce here olive oil is the main source for cooking oil.
Grape cultivation or viticulture is practiced here commercially. A long dry summer is most suitable for grape cultivation. Almost 75% of the World’s wine production comes from here.
- Sherry – Spain
- Port wine – Portugal
- Chianti, Asti, Marsala – Italy
- Champagne, Burgundy, Bordeaux - France
Eastern margin of temperate areas:
Warm moist summer and cool dry winter is seen in this region. These regions occur in the Eastern margins of continents present in the temperate regions. The regions see high annual temperature range.
Due to South East monsoon there is rainfall in summer and North West monsoon leads to rainfall in winters. Typhoons occur in late summer and are disastrous.
In the Gulf of Mexico region of USA there are hurricanes or thunderstorms in summer and local intense heating in winters creates highly destructive tornadoes. This region is also known as the “Tornado Alley”.
The China type climate is modified in the Southern hemisphere due to the moderating influence of the Oceans. The annual temperature range is lower. Hurricanes or typhoons are absent but less destructive weather activity is seen here too.
Natural vegetation is evergreen as rainfall is throughout the year and no dry period is present. The adequate rainfall has made this region the most productive and intensively cultivated region.
Rice is the main crop of China and Eastern margin countries of Asia. Since rice isn’t the staple food of the gulf states , they grow corn and maize, cotton and tobacco. The Corn belt of USA accounts for half of the World’s production but doesn’t export much as a great part of it is used for fattening of Cattle and Pigs. These are sold to slaughter houses and the meat is exported as “corned beef” or “frozen and chilled beef”.
Other commercial crops are cotton and tobacco. The cotton belt is a major producer of cotton and the yield is high. The crop requires conditions like long summer and adequate rainfall. As both are seen here the productivity is high. Tobacco too is grown plenty as it is the native crop of the US.
China type: – Rainfall throughout the year. Typhoons occur in late summer.
Gulf type: – no distinct dry season. Less annual temperature range.
Natal type: - rainfall throughout the year.
Cool temperate western margin [British type]:
This climate sees mild summers and winters and so a low annual temperature range. This season is suitable for maximum mental alertness and productivity. Therefore these regions are known as the Maximum Productivity region of the World.
The mildness of the temperature is also due to the influence of the North Atlantic drift.
There are four seasons: Small winters where snowfall is expected, spring which is dry and refreshing, summer which is long and sunny and then autumn or fall when leaves of trees fall down. Autumn season is a characteristic of the temperate regions as it is absent in tropics.
Warm summer, cool winters. Best for human habitation and low annual range of temperature.
Temperate cyclones give rainfall in winter. Rainfall from Westerlies and so west coast receives the most rainfall.
Cool temperate eastern margin [Laurentian type] and Continental area [Siberian Type]:
Coniferous forests are found in Siberia, Taiga is the greatest single band of coniferous forests. The Siberian type of climate is completely absent in the Southern hemisphere due to the narrowness of continents in the high latitudes as well as the moderating influence of the oceans. Coniferous forest has limited tree species like Pine, Fir, Spruce and Larch.
They are commercially exploited for soft wood. The World’s largest softwood producer is USSR, USA is leader in wood pulp and Canada is leader in Newsprint. A luxurious coniferous forest has made this possible.
Vegetation of non-conifers is low due to harsh conditions like small summers. Conifers have adapted themselves to this climate by showing remarkable features like:
- Conical shape – Snow falls to ground
- Thick, needle shaped, leathery leaves - check excess transpiration. Due to the evergreen nature of trees there is little leaf fall, also low temperature means decomposition rate is less plus the needle shaped leaves are slow to decompose. Podzolized soils of coniferous forests are acidic and hence humus content of soil is low. Thus coniferous forests have low undergrowth.
Not in southern hemisphere as hardly any land below 40 degree. In North America, rainfall throughout the year. Temperate regions have profitable fishing and coniferous forests. Found only in northern hemisphere.
Found between tundra region and Laurentian climate. Very cold winter and warm summer. High annual temperature range. Rainfall throughout the year and temperate cyclones. Found only in northern hemisphere.
Tundra vegetation is seen here in the low lands where a few frost free months are there. Polar climate is seen mostly in the Northern part of North America continent and Northern part of Russia. Ice caps are seen in the Greenland area.
Freezing in winter. Thawing in summer. Aborigines are seen. Ephemeral [short lived] flowering plants. Found only in northern hemisphere.
During La Nina year:
- Walker cells are intensified. This leads to higher rainfall in Australia and higher up-welling in Peru due to which fishes are more.
- India too receives good rainfall.