This article deals with ‘ Migration .’ This is part of our series on ‘Society’ which is important pillar of GS-1 syllabus . For more articles , you can click here .

What is Migration ?

  • Migration refers to  spatial mobility between one geographical unit and another , generally involving change of residence for a considerable period of time .
  • The Census defines a migrant as a person residing in a place other than his/her place of birth or one who has changed his/ her usual place of residence to another place .
  • Migration includes both additive (at place of destination)  as well as separative  (at place of origin) aspects.

Types of Migration in India

  • India has witnessed the waves of migrants coming to the country from Central and West Asia and also from Southeast Asia. In fact, the history of India is a history of waves of migrants coming and settling one after another in different parts of the country. Similarly, large numbers of people from India too have been migrating to places in search of better opportunities especially to the countries of the Middle East, Western Europe, America, Australia and East and South East Asia.
  • Migration can be divided into the following types on the basis of origin and destination:
    1. Rural to Rural R → R (mostly in cases of marriages only) 
    2. Rural to Urban R → U (also known as Urbanisation)  
    3. Urban to Urban U → U
    4. Urban to Rural U → R (very unlikely. It includes doctor or any govt employee going to village for job or reverse migration of the earlier migrant)
  • Other basis of division can be whether within country or outside country
    • Internal Migration – Within same country . Which can  further  be divided into
      • Intra- state : Within State
      • Inter-state  : Between States
    • International Migration – From one country to other country.
  • On the basis of duration
    • Permanent Migration
    • Semi-Permanent (when due to lack of economic resources, people are not able to sustain their living in the destination regions and are forced to migrate back) .
    • Seasonal / Circular ( because of rainfed nature of our agriculture along with the lack of employment opportunities, people migrate to other areas during lean season and come back to the source region once that period is over).

Trends of migration in India

According to Census 2011, 45.36 crore people i.e. 37% of the population or every third citizen of  India   is a migrant —now settled in a place different from their previous residence.  

1 . Intrastate Migration

  • About three-fourths of all intrastate migrants were females corroborating the fact that  marriage is the prime reason for such migration. Most people, 49%, migrate for marriage (while globally, migration is attempt by people to survive and prosper, in India, marriage appears to be the biggest reason why people migrate).
  • Other reasons
    • Rural to Urban in search of good job and educational facilities.
    • Urban to Urban : Due to job transfers etc.

2 . Interstate Migration

  • From underdeveloped states like Uttar Pradesh, Bihar etc. to  comparatively developed regions like Maharashtra , Punjab, NCR Delhi, Chandigarh etc.
  • As per census 2001, Maharashtra occupied first place in the list with 2.3 million net in-migrants, followed by Delhi, Gujarat and Haryana. On the other hand, Uttar Pradesh (-2.6 million) and Bihar (-1.7 million) were the states, which had the largest number of net out-migrants from the state.

Interstate Migration is also of two types with different Destination

2.1 Rural as Destination

  • Mostly agricultural labourers from underdeveloped states coming to Punjab, Haryana etc.

2.2 Urban as Destination

  • These include groups of industrial labourers .
  • Post LPG reforms and ICT revolutions , Migration of skilled professionals in IT sectors  to Bangalore, NCR , Mysore, Hyderabad, Chandigarh etc. where BPOs are  situated .

3 . International Migration

  • Large scale international migration is seen from whole country but especially from Kerala & Punjab .
Kerala Mainly to Gulf Nations
Punjab Mainly to Canada, UK, Australia and to lesser extend to Gulf nations
  • Benefit that these regions are getting huge remittances . But it is an issue of worry because of high brain-drain.
International Migration

Side Topic : Curious Case of Mexican International Migrants

  • Mexico’s emigration problem is a unique one, with more than 98% of all Mexican migrants living in the U.S.A, the country with which Mexico shares a border that runs 3110 km in length.
  • The Mexican emigration rate increased substantially since the 1960s and, with more than 11% of Mexicans living abroad, Mexico is the country with the largest number of emigrants in the world.
Mexican Migration to USA

Side Topic : Brain Drain

  • Brain drain is related to selective migration of educated people . Some countries are losing the most educated segment of their population. It can be both a benefit for the receiving country and a problem to the country of origin.

Impact on receiving country

  • Receiving country gets highly qualified labour which contributes to the economy right away.
  • It promotes economic growth in strategic sectors especially science and technology.
  • Receiving country doesn’t have to pay education and health costs, for example, 30% of Mexicans with a PhD are in the US.

Country of origin

  • Education and health costs are not paid back to the country of origin. It is losing potential leaders and talent.
  • It has long term impact on economic growth. It has the possibility of getting remittances. Many brain drain migrants have skills which they can’t use at home. The resources and technology may not be available there. The specific labour market is not big enough.

Theories of Migration

1 . Ravenstein’s Gravity Model

  • Movement of population gravitates around the centres of socio-economic opportunities . 
  • Distance Decay Principle says that ‘As  distance increases , the tendency to migrate decreases’.

2. Pull-Push Hypothesis

Migration is the result of interplay between expulsive forces at  place of origin and attractive forces at  place of destination.

Push Factors 1. Famine & Floods
2. War
3. Huge Crime Rate
4. Low Jobs
5. Harsh Climate
Pull Factors 1. Better Jobs
2. Education
3. Cleanliness
4. Better Standard of living
5. Better Climate

3. Cost and Benefit Model

Difference between cost and benefits that will accrue after migration determines Migration.

Cost of Migration 1. Cost of travelling
2. Costs of searching job
3. Getting training
4. Psychic costs  etc.
Benefit 1. More earnings
2. Better living standard
3. Enhancement of prestige etc.

Causes of Migration

1 . Push Factors

Factors forcing person to leave his residence and move to some other place

1.1 Economic Causes

  • Lack of jobs
  • Rural Poverty
  • Low levels of Economic development .
  • Development led migration => building dam can force number of villages to be evacuated .
  • Pressure of population resulting in a high man to land ratio .

1.2 Socio-Cultural Causes

  • Caste System : Dalits feel suffocated in villages and hence migrate  .
  • Higher pressure on limited land in bigger families .
  • Marriage : Most people, 49%, migrate for marriage purposes.
  • Family conflicts also cause migration.

1.3 Political Causes

  • Targeted violence against community create fear among the survivors and force them to migrate => Eg: Large Sikh migration from Delhi to Punjab post 1984 riots and exodus of Kashmiri pandits from the valley.
  • Adoption of the jobs for ‘sons of the soil policy’ by the State governments . Eg : The rise of Shiv Sena in Bombay, with its hatred for the migrants and the occasional eruption of violence in the name of local parochial patriotism.

2. Pull Factors

Migrants are lured by the attractive conditions in the new place.

2.1 Economic Causes

  • Economic opportunities & Jobs in cities and abroad .
  • Better standard of living, health & educational facilities etc. 
  • In recent years, the high rate of movement of people from India to the USA, Canada & Middle-East is due to  better employment opportunities, higher wages & better amenities .

2.2 Socio-Cultural Causes

  • Caste don’t play much role in urban areas (due to urban anonymity).

2.3 Political Causes

  • Political freedom in western countries.

3. Pull Back Factors

  • This has been a recent phenomenon. With better opportunities for employment (due to MGNREGA and other schemes, agricultural revolutions) individuals are pulled back to their native places.

Side Topic :  Internal Migration due to disasters

  • India had the highest number of internally displaced people (IDP) due disasters  (five million) in the world in 2019 .
  • 5,90,000 people in India live are internally displaced due to disasters in India as a result of various cyclones like Fani, Vayu, Bulbul etc along with south west monsoon and droughts in various parts.
  • IDPs are different from refugees in that, having not crossed a border, they are not typically covered by international refugee protections. They remain subjected to national laws, and as such are afforded less protection .

Characteristics of the Migrants in India

  • Age selectivity : Most migrants, especially in developing countries are predominantly young adults. Also a major part of the female migration consequential to marriage occurs at the young adult ages.
  • Chain migration : Migrants have a tendency to move to those places where they have contacts and where the previous migrants serve as links for the new migrants and chain is thus formed in the process  .
  • Among women, as expected, marriage was the most important reason for migration, followed by associational migration.

Consequences of Migration

1 . On the destination

  • Creates pressure on urban infrastructure due to increased traffic, competition for housing facilities & water etc.
  • Create social and ethnic tensions due to clash of interests between  migrants and  locals due to rise in prejudice and xenophobia against migrants .
  • Mismanaged migration leads to formation of slums and ghettos and  act as source for outbreak of diseases .
  • It leads to skewed sex ratio in favour of males .

2. On the source

  • Separation of individual migrants from the origin areas & kinsmen .
  • Results in loss of human resource for the state, especially if the migration is of employable people.
  • Migrants acts as agent of social change. Internalised urban values are  transmitted to native place .
  • Impact on women : It leads to ‘Feminisation of labour & agriculture’  at source .   Because of the male migration from Kerala, wives suffer from neurosis, hysteria and depression.
  • Remittances sent by the migrants has the most important impact. Remittances are mainly used for food, repayment of debts, treatment, marriages, children’s education, agricultural inputs, construction of houses, etc. For thousands of the poor villages of Bihar, Uttar Pradesh, Orissa, Andhra Pradesh, Himachal Pradesh etc. internal remittance works as life blood for their economy.
  • Migration leads to evolution of composite culture and broadening of the mental horizon of the people at large.
  • Migration has also changed the demographic profile of the rural areas corroborated by following facts
    • Reduced family size among the migrants as compared to non-migrants. The separation of the rural male migrants from their wives for long durations tends to reduce the birth rate.
    • Ageing of Villages as migrants are young leaving old age in villages .  
    • Increased Sex Ratio in villages as men usually migrate leaving females behind.

3. On migrants

  • Problem of document and identity which deprives them of social security benefits and government socio-economic programs.
  • Migration and slums are inextricably linked. Most slums are inhabited by the migrants. Such slums are deprived of basic healthcare and sanitation facilities. 
  • Limited access to Formal Financial Services results in them being exploited by their employers and they face risk of theft and personal injury in saving and transferring their earnings.
  • They face political exclusion because most of the times they don’t have voting rights at the destination. Further they are target of political rhetoric of local identity politics and  subjected to violence and abuse.
Consequences of Migration

Legal measures

  • Inter-State Migrant Workmen Act, 1979, required all establishments who hired inter-state migrants to be registered, as well as all contractors who recruited these workers to be licensed.
  • During Covid times (in 2020) and problems faced by the migrants during that time, need was felt to create a database to map migrant workers scattered across the country. Hence, Government has  decided to create a database of migrant workers using existing  databases of government schemes such as MGNREGA, and the one nation-one ration card .

Way forward

  • There is a legislation i.e. Interstate Migrant Workmen Act, 1979 which aims to safeguard migrants . However , it is obsolete and hardly enforced . Need of the hour is the judicial implementation of the act in letter and spirit .
  • Rather than treating migration as problem, destination states should aim to accommodate them into the economy of the state. There is ample evidence to support the fact that migrants generally take up those jobs and businesses which are not done by the locals.
  • The planning of cities should keep in mind the needs of the migrants.
  • Political class, civil society and NGOs should conduct inter group interactions to ward off mistrust between natives and migrants.

Honour Killing

Honour Killing

This article deals with ‘ Honour Killing (UPSC) .’ This is part of our series on ‘Society’ which is important pillar of GS-1 syllabus . For more articles , you can click here .


According to Britannica , Honour Killing is the murder of a woman or girl by male family members. The killers justify their actions by claiming that the victim has brought dishonour upon the family name . 


Problem of Honour killing is quite complex & reasons vary in different areas.

  • Feudal Mindset  :  woman marrying outside her community brings dishonour to the family and it is better to kill them and set example for others .
  • Strike against Dalit Assertion  especially when women is from OBC caste & boy from Dalit caste .
  • Inter religious marriages : Politicisation of matter  especially in  UP  and ‘Love Jihad’ campaign by Hindutva ultra right wing.
  • Same Gotra Issue in Haryana : In Haryana, marriages between couples belonging to the same gotra  are not recognised leading to incidents of honour killing.
  • Law Commission of India observed that one of the reasons of honour killing is change in economic status of women and taking a stand against the male-dominated culture.

Law regarding this

But, inspite of the increase in the number of crimes in the name of honour there is

  • no definition of the crime
  • no protections legally afforded to  couple

Special law like Scheduled Caste/Scheduled Tribe Prevention of Atrocities Act could render some justice to the victims of honour killings.

Judgements wrt Honour Killing

1 . Shakti Vahini Case (2018)

  • NGO Shakti Vahini filed PIL in Supreme Court.
  • Supreme Court gave various guidelines to end honour killings like
    1. State Government should identify districts where honour killing happened in last 5 years .
    2. Khaps  should not act as they are conscience-keepers .
    3. Police should help couples . 
    4. Safe Houses for couples (1 month to 1 year) .
    1. Fast Track Courts should be made to decide case within 6 months .

Earlier Judgements regarding Honour Killings

2. Supreme Court Judgement on Khap Panchayats (2011)

In 2011, Supreme Court termed

  • Khaps were termed as “kangaroo courts” .
  • They were declared them illegal .
  • Court wanted them to be stamped out ruthlessly. 

3. Lata Singh v. State of U.P.

  • Inter-caste marriages are in fact in the national interest as they will result in destroying the caste system.

4. Bhagwan Das v. Delhi  (2011)

  • Supreme Court deemed honour killings in the “rarest of rare” category of crimes that deserve the death penalty.

Feminisation of Agriculture

Feminisation of Agriculture

This article deals with ‘Feminisation of Agriculture .’ This is part of our series on ‘Society’ which is important pillar of GS-1 syllabus . For more articles , you can click here .


  • Feminisation of agriculture means the increasing visibility and participation of woman in agriculture .
  • Women constitute close to 35 % of all agricultural workers (NSSO 2011-12).
  • However , they are joining agriculture as agrarian proletariat /labour class (& not as owners) .

Feminisation of Agriculture


  • Migration of Males  from rural areas to cities leaving behind  agricultural chores to women. This trend in the agriculture sector was most visible during 1999-2005 marked by declining agriculture growth rates which saw a distress migration of male members to relatively better paying jobs either in the urban informal economy or the agriculturally prosperous states .
  • Widowhood forces woman to till the land to feed family. 

Has this led to women empowerment ?

Yes, it has

It has increased participation of women in the workforce & helped them to

  1. Acquire financial independence 
  2. Imbibe decision making skills.

No , it hasn’t

  • Feminization of Agriculture is not an intended consequence but an unintended impact of distress migration .
  • Due to patriarchal nature of society, they are referred as flexible labours . Hence, they are joining the sector as an agrarian proletariat .
  • Although they are participating in the agriculture but they don’t have  land rights.
  • Because of rural sector schemes like MGNREGA,  men are migrating back  and women are  again confined to  domestic spheres (phenomenon known as ‘de-feminization of agriculture’) .


  • Lack of Property Rights : Given the social and religious set up in India, women do not generally enjoy equal property rights as their male counter parts .
  • Women also have poor access to credit, irrigation, inputs, technology and markets.
  • Agricultural implements are designed for men .

What steps can  government take in view of feminization of Agriculture ?

  • Gender responsive agricultural budgets and  policies are the need of the hour.
  • More property rights should be provided to women .
  • Machines like tractors should be specifically designed for women .
  • Women should be provided preferential membership in the rural cooperatives.
  • Formation of Agricultural SHG for women.
  • Providing creche facility to such women farmers  .

Steps taken by Government

  • 15 October is celebrated as ‘Women Farmers day‘ .
  • Atleast 30% budget allocation should be provided to women beneficiaries in all schemes & programs (including agriculture) .
  • Low duty and tax if land transfer is on women name in some states like Punjab.
  • Women Agricultural Self Help Groups (SHGs) are being promoted by the government.

Side Topic : Defeminisation of Agriculture

  • Due to schemes like MGNREGA, men who earlier migrated to other areas in search of jobs have started to come back. This has led to reverse process known as Defeminisation of Agriculture .

Concept : Feminization of work

It has three dimensions

  1. When more number of females are working
  2. When there is increased concentration of woman in certain jobs
  3. When men start participating in the work that was traditionally domain of women (Eg : cookery)

Contract Farming

Contract Farming

This article deals with ‘Contract Farming.’ This is part of our series on ‘Economics’ which is important pillar of GS-3 syllabus . For more articles , you can click here .


It is a forward agreement between farmers & buyers  in which

Buyer – Agrees to buy produce from farmer at predetermined price &
– Usually provides inputs (Seeds, fertilizers, pesticides), technology and production practices so that final produce meets his desired quality.
Farmer – Agrees to grow and supply the produce to the buyer at predetermined quality, quantity and prices.

But problem is,  this is prevalent in only few states where APMC laws allow this  

Punjab 1. PepsiCo doing contract farming with Potato farmers of Hoshiarpur district.
2. ITC doing contract farming for Soyabean.
3. Mahindra Shubhlabh doing contract farming for Basmati rice.
Karnataka Himalaya doing contract farming with Ashwagandha producers.
Madhya Pradesh Hindustan Unilever doing contract farming with wheat farmers.

In news because

  • Model Contract Farming Act was released by the government.
  • It is Important component  in doubling farmers income .

Benefits of Contract Farming

  • Improving Farmer’s Productivity : It provides  access to better inputs, scientific practices and credit facilities .
  • Insurance to post harvest price fluctuations : Prices are fixed, hence farmers are saved from price fluctuations .
  • Crop Diversification : Otherwise farmers grow only wheat and rice which is procured by Government .
  • Helps in promoting Food Processing Industry .
  • Company can get desired quality of agro products .
  • Consumers Benefit : Elimination of intermediaries can  reduce food price inflation.

Challenges with Contract Farming

  • Stockholdings limits on contracted produce under Essential Commodities Act, 1955  .
  • Not benefiting Small Farmers: Buyers have no incentive for contract farming with a large number of small and marginal farmers due to high transactions and marketing costs, creating socio-economic distortions and preference for large farmers
  • It is a capital-intensive and less sustainable pattern of cultivation as it promotes increasing use of fertilizers and pesticides which have detrimental impact on natural resources, environment, humans and animals.
  • Encourages Monoculture Farming: This will not only impact soil health but also pose risk to food security .
  • Monopsony: Product is generally special crop and for that company is the only buyer. Hence, farmer can be price taker only because company is the sole buyer .
  • Predetermined prices denies farmer the  benefits of higher prices  prevailing in the market  .

Key Features of Contract Farming Act

  • Mainly to address issue of breach of contract by the company (because company can breach contract if they are getting goods at cheap price and then afford lawyer to fight case) .
  • It sets up Contract Farming Authority and Recording Committees to register the contracts and implement them effectively .
  • It provides to keep contract farming outside the ambit of APMC act .
  • The produce will be insured under the existing agriculture insurance schemes.
  • It makes provisions for making farmer producer Companies (FPCs).

Income Inequalities

Income Inequalities

This article deals with ‘Income Inequalities.’ This is part of our series on ‘Economics’ which is important pillar of GS-2 syllabus . For more articles , you can click here .


  • Income inequality is the degree to which income is unevenly distributed throughout the population.
  • It is measured statistically using Gini Coefficient.
  • Apart from that, Oxfam also releases a report every year showing the income inequality in the world and India.

Gini Coefficient

  • Gini Coefficient is a statistical measure to gauge income inequality or wealth divide .
  • It’s value vary between 0 to 1 ; 0 indicating perfect inequality and 1 indicating perfect equality.
  • An increase in value of Gini Coefficient means that inequality in an economy is increasing and government policies are not inclusive and benefitting richer .

Calculation of Gini Coefficient

  • Gini Coefficient is a statistical measure to gauge income inequality or wealth divide .
  • It’s value vary between 0 to 1 ; 0 indicating perfect inequality and 1 indicating perfect equality.
  • An increase in value of Gini Coefficient means that inequality in an economy is increasing and government policies are not inclusive and benefitting richer .

Calculation of Gini Coefficient

  • Gini Coefficient = A / (A+B)
Gini Coefficient

In the graph shown above

  • Horizontal axis on this chart represents cumulative shares of the population.
  • Vertical axis is cumulative shares of income.
  • A+ B is constant and if
    • A is higher, it means inequality is higher .
    • A is smaller, it means inequality is lower.
    • If A = 0 , then no income inequality.
  • Hence, Gini Coefficient is measured from 0 to 1 and lower value means low inequality and higher means more inequality .

Kuznet Curve on Inequality

  • Famous US Economist Simon Kuznet showed that as an economy develops, market forces will first increase inequality and then decrease inequality among people.
  • This happens because the initial phase of economic growth boosts the income of workers and investors who participate in first wave of innovation . But this inequality is temporary as other workers and investors soon catch-up resulting in improvement of their incomes as well.
Kuznet Curve

India and Income Inequality  

  • Piketty the world famous economist have cautioned India for rising levels of Income inequalities and its consequences. In country like India where other forms of inequalities are present too most important being caste system, income inequalities exacerbates the situation .
  • India grew at average rate of 7.5% since 2011 but growth is not equally distributed (rich are growing more)  . Gini Coefficient shows that income inequality is continuously increasing in India . The following data corroborates this 
Gini Coefficient of India
  • According to Oxfam Report (2020) , India’s top 1% wealthy people hold 42.% of the National Wealth  while the bottom 60% own less than 5%.
Income Inequalities
  • According to Oxfam head , it is morally outrageous that a few wealthy individuals are collecting growing share of India’s wealth , while the poor are struggling to find their next meal . If this obscene inequality continues, it will lead to complete collapse of social and democratic structure of this country.

Causes of Income Inequality

Historical Causes Caste System : Due to exclusion of lower caste from ownership of land and education , people belonging to lower caste are poor .  
Social Causes Caste System is the main reason.
Due to patriarchal and patrilineal nature of Indian society, Women don’t own factors of production in India.
Frequent Global Economic Crisis Economic Crisis like that happened in 2008 accentuate income inequality by making richer rich and poorer poor . 

(How= Central Bank cant allow big houses to fell . Due to this, they get large cuts . Currency devaluate and Amount of loans that companies have to pay decrease in reality. On the other hand, households who have deposited their money loose value of their money)  
Faulty taxation system In India , there is more reliance on Indirect Tax which is regressive in nature . Apart from that, government has removed wealth tax in India.  
India relied on  trickle down approach India relied on ‘Trickle Down Approach’ which benefitted the industrial houses and rich businessmen. In order to reduce inequality, India should have followed  redistributive justice principles of John Rawls, Gandhian trusteeship principles or Amartya Sen’s capability approach.    
Technological Change Rapid technological changes is leading to automation of industries . As a result, few people with high skills are getting high packages while large number of workers are losing their jobs .  
Capture of power by elites Due to Crony Capitalism , political leaders and government is working as agents of elites . Policies of government are made in such a way that it benefits elite sections of the society.    

Consequences of Inequalities

Conflicts  and Insurgency – Arab Spring of 2011 in the Middle-East  was result of high inequalities in that region .
Earlier in India, Naxalbari Movement was result of inequality (in land holding)  
Crimes It has been observed that unequal societies have higher crime rates. Poverty force people to earn via illegal means .  
Political Impacts In case of higher income inequalities, political democracy and government starts to loose its legitimacy.  
Effects on Growth Income distribution matters for growth. If income is more equally distributed, it means more potential buyers of goods creating bigger markets.

Steps Taken by India

Tax Reforms  Piketty has suggested India to improve its Tax : GDP which is abysmally low .
Indian Government is taking steps to bring more people in tax net. Taxation system helps in ‘redistribution of money’ from richer to less well off.  
Skill Development Improving education quality, eliminating financial barriers to higher education, and providing support for apprenticeship programmes .  
Social Security The high cost of healthcare and medicines drives a hundred million people into poverty every year.  For the very poorest and most vulnerable there must be a universal and permanent safety net that is there for them in the worst times. Government has taken various measures in this regard like starting Ayushman Bharat Scheme.  
Various steps against Black money Steps like demonetization have been taken by the government to control black money .

Humidity, Condensation, Clouds and Precipitation

Humidity, Condensation, Clouds and Precipitation

This article deals with ‘Humidity, Condensation, Clouds and Precipitation’ This is part of our series on ‘Geography’ which is important pillar of GS-1 syllabus . For more articles , you can click here


  • Water vapour present in the air is known as humidity. 
  • It is expressed quantitatively in different ways like 
Actual Humidity Actual amount of the water vapour present in the atmosphere.
Relative Humidity The ability of the air to hold water vapour depends entirely on its temperature. The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity .
Specific Humidity Ratio of weight of water vapour to weight of dry air.
Vapour pressure Part of barometric pressure that is caused by water vapour alone.
  • The air containing moisture to its full capacity at a given temperature is said to be saturated. It means that the air at the given temperature is incapable of holding any additional amount of moisture at that stage.
  • The temperature at which saturation occurs in a given sample of air is known as dew point.

Evaporation & Condensation

1 . Evaporation

  • Evaporation is a process by which water is transformed from liquid to gaseous state.
  • It can occur in three conditions
    • High temperature
    • Low Pressure conditions
    • Fast moving wind

2. Condensation

  • Condensation is process of conversion of water vapours present in air into water droplets .
  • Condensation is caused by the loss of heat. When moist air is cooled, it may reach a level when its capacity to hold water vapour ceases. Then, the excess water vapour condenses into liquid form.
  • Condensation takes place:
    • When the temperature of the air is reduced to dew point  or When moisture is added to the air  
    • Surface : Which may be natural like grass etc (making dew) or Hygroscopic Surface/ Nuclei

3. Sublimation

  • If water vapour directly condenses into solid form, it is known as sublimation.

Dew, frost, fog and clouds

After condensation, the water vapour or the moisture in the atmosphere takes one of the following forms — dew, frost, fog and clouds.

1 . Dew

  • When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects such as stones, grass blades and plant leaves, it is known as dew.
  • The ideal conditions for its formation are calm air, high relative humidity, and cold and long nights.
  • For the formation of dew, it is necessary that the dew point is above the freezing point (otherwise frost will form) .

2. Frost

  • Frost forms on cold surfaces when condensation takes place below freezing point (0 C).

3. Fog

  • When temperature of an air mass containing a large quantity of water vapour falls all of a sudden below dew point, condensation happens and subsequent cloud  is formed at ground level. This is known as fog.
  • Fogs are mini clouds in which condensation takes place around nuclei provided by the dust, smoke, and the salt particles.
Radiation fog Associated with temperature inversion & formed at cold night when temperature of air near ground falls below dew point .
Most common type in winter season.
Frontal fog When cold air masses converge against warm humid air masses , cold air being heavy remains at bottom while warm air is pushed over leading to cooling & formation of fog
Famous fog of Newfoundland is formed like this.
  • In fog, visibility is less than 1 km.

4. Smog

  • Fog + Smoke = Smog.
  • In urban and industrial centres, smoke provides plenty of nuclei which help in the formation of fog . Such a condition when fog is mixed with smoke, is described as smog.
  • It is associated with very low visibility and health hazard.

There are two type of Smog

a . Sulphurous Smog

  • Aka London Smog
  • Results from high concentration of Sulphur Oxides in the air caused by use of Sulphur containing fossil fuels , particularly Coal .
  • Occur in cool humid climate
  • Chemically reducing hence called reducing smog
  • Characterised by blue coloured skies aka blue haze.

b. Photochemical Smog

  • Occurs in warm, dry & sunny climate
  • Results from the action of sunlight on unsaturated Hydrocarbons & oxides of Nitrogen produced from factories and automobiles.
  • Chemically Oxidising and hence called Oxidising Smog
  • Ozone, PAN (Peroxyacetyl Nitrate), Acrolein & Formaldehyde are produced in it which can cause serious health problems .

5. Mist

  • The only difference between the mist and fog is that mist contains more moisture than the fog.
  • In mist, each nuclei contains a thicker layer of moisture.
  • Mists are frequent over mountains as the rising warm air up the slopes meets a cold surface.
  • Visibility is more than 1 Km but less than 2 km.

Visibility Comparison : Mist > Haze  > Fog > Smog.

6. Cloud

  • Cloud is a mass of minute water droplets formed by the condensation of the water vapour in free air at considerable elevations.
  •  As the clouds are formed at some height over the surface of the earth, they take various shapes


  • Clouds are tiny water droplets suspended in the air formed due to the condensation.
  • To understand the nomenclature of Clouds, one must be aware of the meaning of some Latin words.
Cirrus Curl of hair/ high .
Cumulus Heap or pile of cotton.
Strato Sheet or layer.
Nimbo Rain.
Alto Middle altitudes.

Classification of Clouds

The clouds can be classified based on their form, height and appearance as follows:

Classification of Clouds

1 . High Clouds

Different types of Cirrus clouds are present above height of 6Km

1.1 Cirrus Clouds

  • They look like curl of hair
  • It indicates fair weather and gives brilliant sun set.

1.2 Cirro Cumulus 

  • This appears as white globular masses, forming a mackerel sky.

1.3 Cirro Stratus 

  • This resembles a thin white sheet. The sky looks milky and the sun and moon shines through this clouds and form a ‘halo’

2. Middle Clouds

Different types of  Alto clouds  are found between 2 km to 6 km above the ground.

2.1 Altocumulus

  • These are woolly, bumpy clouds arranged in layers appearing like waves in the blue sky.
  • They indicate fine weather.

 2.2 Altostratus

  • These are denser and have watery look.

3. Low Clouds

Mainly Stratus or sheet clouds below 2 km height.

3.1 Stratocumulus

  • This is rough and bumpy clouds with wavy structure.

3.2 Stratus

  • This is very low cloud, uniformly grey and thick, appears like highland fog.
  • It brings dull weather and light drizzle. It reduces the visibility and is a hindrance to air transportation.

3.3 Nimbostratus

  •  This is dark dull cloud, clearly layered, as it brings gentle rain, snow and sleet and it is called as rainy cloud.

4. Clouds with vertical extend

These are mainly cumulus clouds whose  height extend from 2 km to 10 km approximately.

4.1 Cumulus

  •  This is vertical cloud with rounded top and horizontal base, associated with convectional process in the tropical region.

4.2 Cumulonimbus

  • This is over grown cumulus cloud with great vertical extent, with black and white globular mass.
  • This is formed due to heavy convection in the tropical regions. It is accompanied by lightning, thunder and heavy rainfall


Precipitation is the process by which all forms of water particles fall from the atmosphere and reach the ground.

Conditions necessary for precipitation

  • Air parcel must be cooled below dew point.
  • Presence of condensation nuclei(i.e. minute hygroscopic particles serving as nuclei for water particles) in the air . Eg salt, smoke & dust particles=> if they aren’t present, precipitation will not occur even if relative humidity is above 100% .
  • Condensation must occur rapidly & for fairly long time . If occur for small time  , then it may not reach to earth as it would be absorbed by unsaturated air present in lower parts .

Forms of precipitation

1 . Rainfall

  • Most common type of precipitation in temperate & tropical regions.
  • When water droplets of more than 0.5 mm diameter falls from the atmosphere to the ground it is called as ‘Rainfall’.
  • If the diameter is less than 0.5mm, it is called as ‘Drizzle’.

2. Hail

  • When condensed moisture in form of raindrops is carried to great heights by strong convection currents & they get frozen due to low temp at greater heights=> when they come down they gather more water around them & size of pellets become large.
  • Ice pellets has size of 5 to 50 mm or some times more. 

3. Snowfall

  • Precipitation occurs at below freezing point and falls as thin ice flakes or powdery ice, called  ‘Snow’.

4. Sleet

  • Precipitation in the form of mixture of raindrops  & ice pellets less than 5 mm in diameter.
Forms of precipitation

Types of  Rainfall

Since rainfall is the major type of precipitation, we will look of type of rainfalls. It can be of various types depending upon process of rising up of air

1 . Convectional Rainfall

  • As a result of heating of the surface air, the warm moist air expands and is forced to rise to a great height. As the air rises, it cools, reaches dew point and condenses to form clouds.
  •  Cumulonimbus clouds are formed in this .
  • This type of rainfall occurs
    1. Throughout the year near the equator in the afternoon. It is called as 4 ‘O’ clock rainfall region.
    2. In middle latitudes, convectional rainfall occurs in early summer in the continental interiors
Convectional Rainfall

2. Orographic Rainfall

  • Air is forced to move up by landform features like   mountain, plateau , escarpment etc and air thus rising may cool below dew point causing rain.
  • Windward side gets heavy rain whereas leeward side is rain shadow area.
  • Most of rain occurring in India and world is orographic . In India, Western coast & North East India gets rainfall by this process.
Orographic Rainfall

3. Cyclonic Rainfall

  • This type of precipitation is associated with a cyclonic activity (Tropical and Temperate cyclones)
  • Cyclonic rainfall is associated with Cumulo-Nimbus  clouds. The rainfall is very heavy and accompanied with lightning and thunder and high speed winds which has the potential to cause damage.

4. Frontal Rainfall

  • ‘Frontal rainfall’ is associated with fronts which form due to collision of different air masses.
  • It can be of two types
    1. Warm Air Front Rainfall : In this , warm air invades cold air leading to formation of Nimbostratus clouds and gentle rainfall.
    1. Cold Air Front Rainfall : In this, cold air invades warm air leading to formation of Cumulonimbus cloud and violent rainfall with lightening.

Wind Systems

Wind Systems

This article deals with ‘Wind Systems’ This is part of our series on ‘Geography’ which is important pillar of GS-1 syllabus . For more articles , you can click here


  • Wind is the horizontal movement of air molecules from areas of high pressure to areas of low pressure to maintain the atmospheric equilibrium.
  • Nomenclature of Winds
    • Winds are named easterly, westerly, northerly etc on basis of direction of their origin.
    • Easterly wind is that which originate in east & blow from east to west.
  • Wind direction is identified by an instrument called Wind Vane and wind speed is measured by Anemometer.

Factors affecting direction & velocity of wind

1 . Pressure Gradient

  1. If pressure gradient is more, velocity will be more in magnitude because differences in atmospheric pressure produces a force.
  2. The wind always moves perpendicular to isobars.

2. Frictional Force

  • Lower is frictional force, greater will be the speed .
  • Over the sea surface the friction is minimal.

3. Coriolis Force

  • If the earth did not rotate, the winds would blow in a straight path. Then the rotation of the earth results in Coriolis effect and it deflects the direction of the wind.
Northern Hemisphere Deflect towards Right or Clockwise (NCR)
Southern Hemisphere Towards Left or Anticlockwise.
  • Coriolis force is directly proportional to the angle of latitude. It is maximum at the poles and is absent at the equator.

Type of Winds

Type of Winds

1 . Primary / Global/ Permanent Winds

Pressure belts lead to the formation of primary wind system resulting in Trade Winds, Westerlies and Polar Easterlies

1.1 Trade Winds

  • The winds blow from the sub tropical high pressure belt towards the equatorial low pressure belt.
  • Due to Coriolis Effect, these winds are deflected to the right in the northern hemisphere and to the left in the southern hemisphere.
  • As winds are named after the direction from which they originate they are called as the North East and South east trade winds.
  • As the winds favoured trading ships they are called as ‘Trade winds’.

Side Topic : Tropic Deserts & Trade Winds (aka Trade Wind Deserts or Trade Deserts)

  • Tropical easterlies/ Trade Winds flow from east to west  . Hence, windx becomes dry when they reaches the western coast of continent as all the moisture  is already shed in form of rainfall on eastern coast .As a result, in tropical region, deserts are found on western coasts of continents .They are also known as Trade Deserts.
  • Apart from that, Cold Currents near the western coasts of continents also provides desiccating imapct on the surrounding lands leading to more dryness .

1.2 Westerlies

  • Westerlies flow towards the Sub Polar High from Sub-Tropic Low
  • They turn towards right and left in northern and southern hemisphere respectively due to Coriolis force.
  • As they flow from West to East, they are called Westerlies
  • Ocean is dominant in the southern hemisphere between the latitudes 40º and 60ºS. Hence the westerlies are so powerful and persistent that the sailors used such expressions as “Roaring Forties”, “Furious Fifties” and “Screeching Sixties” for these high velocity winds in the latitudes of 40º, 50º and 60º respectively.

1.3 Polar Easterlies 

  • Polar Easterlies  flow towards the Sub Polar High from Polar High .
  • They turn towards right and left in northern and southern hemisphere respectively due to Coriolis force.
  • As they flow from East to West, they are called Easterlies

2 . Secondary / Regional / Seasonal Winds

Monsoon and Cyclones are considered to be Secondary or Seasonal Wind

2.1 Monsoons

  • Monsoons are seasonal winds which reverse their direction due to various reasons .
  • These winds bring rainfall in India and are the major climatic feature of climate of Indian Sub-continent.
  • We will detail with these winds in Indian Climate .

2.2 Cyclones

  • Wind blowing in circular manner around an area of low pressure 
  • Due to Coriolis effect – blow in anticlockwise direction in Northern hemisphere & clockwise direction in southern hemisphere.
  • Cyclones are of two types.
Tropical cyclones Develop over oceans in summers in tropical regions . Eg : in Bay of Bengal, China sea , Caribbean sea etc.
Temperate / Extra tropical Develop in middle latitudes in winter season

More about cyclones in separate article

3. Tertiary / Local Winds

Tertiary winds are formed due to pressure gradients which may develop on a local scale because of differences in the heating and cooling of the earth’s surface.

3.1 Sea and Land Breezes

  • Sea Breeze :  During daytime, land heats up much faster than water. The air over the land warms and expands leading to formation of low pressure. At the same time, the air over the ocean remains cool because of water’s slower rate of heating and results in formation of high pressure. Air begins to blow from high pressure over ocean to the low pressure over the land. This is called as ‘Sea breeze’.
  • Land Breeze : During night time, the wind blows from land to sea and it is called as ‘Land breeze’
Sea and Land Breezes

Note :  Sea breeze and land breeze influence the movement of boats near the coastal region and fisher men use these winds for their daily fish catching. Fishermen go for fishing at early morning along the land breeze and return to the shore in the evening with the sea breeze.

Sea and Land Breezes

3.2 Mountain and Valley Breezes

  • Valley Breeze / Anabatic Winds  : During the day, mountain hillslopes are heated intensely by the Sun, causing the air to expand and rise. This draws in air from the valley below, creating a valley breeze.
  • Mountain Breeze / Katabatic Winds  :  During the night the hillslopes get cooled and the dense air descends into the valley as the mountain wind

3.3 Warm and Cold Local  Winds

Warm and Cold Local  Winds

Cold Local Winds

  • High Pressure  conditions are created in areas situated in high latitudes due to cold weather. As a result,   air starts to come down and diverge into different directions (forming anti-cyclones) blowing as ‘Cold and Dry Local Winds’ and reducing temperature of surrounding regions as well.
  • In Siberia such anti cyclonic winds are created and diverge in different directions  . These winds are called Buran
Buran Explained above
Mistral (Europe) Cold northerly from central France and the Alps to Mediterranean
Bora (Eastern Europe) North easterly wind from eastern Europe to north eastern Italy
Blizzard (USA & Canada) Cold and dry snowy winds blowing in USA and Canada
Pampero (Argentina) Cold and dry wind blowing in Pampas of Argentina
Southern Bursters Cold and dry wind blowing in  Australia

Warm Local Winds

  • Low  pressure develops  over Deserts and low latitudes in summers due to excessive heating of land . The air starts to move upward and diverges in different directions blowing as upper tropospheric wind. They carry sand and dust with them and raises temperature of regions over which they flow. These winds are known with different names in different regions like
Loo India (Punjab, Haryana, Rajasthan, UP, Delhi etc)
Sirocco From Sahara desert to Italy and Spain after crossing Mediterranean Sea
Khamsin Egypt
Harmattan From Sahara desert to Gulf of Guinea
  • Other  type of warm and local winds like Chinook winds develop when warm, moist air blows from the adjoining ocean ( Pacific Ocean in this case) towards the Mountain range situated near the coast (Rockies in this case). In such situation, dry and warm air over the mountain will descend in the adjoining valley on the leeward side of wind .  Other such type of winds are Fohn and Zonda
Chinook US and Canada Rockies
Fohn Europe Alps
Zonda Argentina & Uruguay Andes
Santa Ana California Santa Ana Mountains
Chinook , Fohn , Conda

Upper Atmospheric / Meridional  Circulations

Hadley cycle Air from equator being lighter move up & diverges toward poles & descends at subtropical areas causing higher pressure there. That wind is again carried by trade winds to equator.
Ferrel Cycle Same  thing between subtropical & subpolar pressure belts
Polar cell  Between polar & subpolar pressure belts
Meridional  Circulations

Side Topic : Upper Tropospheric Winds and Geostrophic Winds

To understand formation of Jetstreams, it is important to know what are Geostrophic winds.

  • Unlike air moving close to the surface, an air parcel in the upper troposphere moves without a friction force because it is so far from the source of friction—the surface. So, there are only two forces on the air parcel, the pressure gradient force and the Coriolis force.
  • A useful heuristic (i.e. theoretical model) is to imagine that air parcel in the upper troposphere is starting from rest under the influence of ‘Pressure Gradient Force ”  moving from point of High Pressure to Low Pressure .
  • Due to pressure gradient force and absence of friction force , speed of wind will  keep on increasing . Since, Coriolis force increases with increase in speed and acts perpendicular to Pressure Gradient Force,  situation will be reached when Pressure Gradient Force equals Coriolis Force  & these winds will deflect 90° (clockwise) . At this point, the flow is no longer  from high to low pressure, but parallel to the isobars. Such winds are called Geostrophic winds
Geostrophic Winds
  • These are also known as Upper Tropospheric Westerlies
  • Jetstreams are an example of Geostrophic winds .

Direction of Geo Strophic winds

Always move from WEST TO EAST  (hence called Westerlies)

Northern Hemisphere Geostrophic winds deflect clockwise .
Move from West to East.
Southern Hemisphere Geostrophic winds deflect Anti Clockwise.
Move from West to East.


  • Jet streams are special type of Geostrophic winds .
  •  These are strong and narrow bands of meandering wind blowing at height of 6 to 14 km ( just below Tropopause) at very high speed of upto 450 Km/hr. They occur at points where atmospheric pressure gradients are strong and friction force acting on moving air is absent.
  • Jetstreams flow in wavy fashion and create alternate   High Pressure & Low Pressure zones .

Location of Jet Streams

  • They aren’t found arbitrarily . They are situated at typical positions like  where two Meridional Circulations meet. (Reason : Point where  two air masses of different temperatures meet, the resulting pressure difference is highest.  Only in such condition, Pressure Gradient Force can increase the speed of wind to such an extend that Coriolis Force can balance the Pressure Gradient Force and rotate it by 90°) (I know it is hard to understand. To properly understand what is happening, you can refer this useful video What is the jet stream and how does it affect the weather?)
  • Hence , 4 permanent Jet streams are always found .
2 Polar Jet  Between Polar cell & Ferrel cell.
2 Sub Tropical Westerly Jet  (STWJ) Between Ferrel cell & Hadley cell.
Jet Streams

Apart from that, there are some temporary Jet-streams like

  • Tropical Easterly Jetstream
  • Somali Jetstream

Speed of Jetstreams

  • Cause of Jetstreams is the pressure difference (due to temperature difference) in the upper atmosphere. Hence , higher the pressure gradient (or temperature gradient) higher will be speed of Jetstream.
  • Temperature variations are more in winters (lowest ~ -70 C & highest ~ 15 C) compared to summers (lowest ~ 20 C & highest ~ 55 C) . Hence, Jetstreams are faster in winters of the respective hemisphere.

Importance of Jetstreams

1 . Sub Tropical Westerly Jet Stream (STWJ) & Indian Weather

  • It is centred around 25° N & S at altitude of 12 km & is strong in winter season with velocity of 40 mph.
  • It greatly determines the weather of Indian Sub continent .
    1. During summer until it is present over Indian subcontinent , High Pressure is maintained over there & monsoon can’t start. Only when STWJ moves above Himalayas & low pressure is created over Indian subcontinent  , monsoon hits India.
    2. Western Disturbances : STWJ comes to India after passing over Mediterranean Sea where rainfall occurs during  winter. STWJ bring those cyclonic disturbances to north India along with it. This results in winter rain & hailstorms in North India  & occasional high snowfall in hilly areas  .

2. Jetstreams and Frontal / Temperate Cyclones

  • Jetstreams play important role in formation of Temperate Cyclones which are important feature of the climate of temperate regions like Britain etc .

3. Tropical Easterly Jet and Somali Jetstream

  • These Jetstreams play important role in the Indian Monsoon.
  • More about this can be read in (chapter) Indian Climate .

4. Role in Aviation Industry

  • If aeroplanes moves in the direction of Jetstream, it can lead to large fuel savings and vice-versa

Impact of Climate Change on Jetstreams

Due to Climate change and Global warming, Earth’s Polar regions are warming more rapidly than other parts . This has resulted in weakening of Polar Jet Streams because temperature contrast that drives Jetstreams has decreased.

Pressure and Pressure Belts

Pressure and  Pressure Belts

This article deals with ‘Pressure and  Pressure Belts’ This is part of our series on ‘Geography’ which is important pillar of GS-1 syllabus . For more articles , you can click here

Atmospheric Pressure

  • Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air molecules above the earth surface.
  • Atmospheric pressure is measured by an instrument called ‘Barometer’
  • The atmospheric pressure is not distributed uniformly over the earth. The  amount of pressure increases or decreases, according to the amount of molecules, that exerts the force on the surface.
    1. When temperature of air increases, the air expands and reduces the number of molecules over unit area leading to reduction in pressure.
    2. Similarly, when the temperature falls, the air contracts and the pressure increase.
Atmospheric Pressure

Factors affecting Atmospheric Pressure of area

1 . Temperature

  • As the temperature increases, air expands because of which its density decreases resulting in low pressure over area.
  • On the other hand, cold climate makes air denser resulting in high pressure over area.
  • Equatorial regions have low pressure because of high temperatures. On the other hand Polar regions have high pressure due to low temperature.

2. Height from Sea

  • The pressure at sea level is highest and keeps on decreasing rapidly with increasing altitude because of the progressive reduction of the mass above the point where it is measured.
Impact of height on pressure

3. Humidity

  • Water vapours are light in weight therefore pressure of humid air is less compared to dry air.

4. Gravitation of Earth

  • Atmosphere glues around the Earth due to its gravitation
  • Due to shape of earth,  Polar regions are nearer to core of the Earth as compared to Equatorial regions and hence have higher air pressure.

5. Rotation of Earth

  • Rotation of Earth results in centrifugal force.  Centrifugal force pushes things away from its core.
  • Centrifugal force is highest over equator and zero over poles. Hence,  air pressure will decrease in Equatorial regions as compared to that in polar regions.

Distribution of Atmospheric Pressure

Horizontal distribution of pressure is studied by drawing isobars . Isobars are lines connecting places having equal pressure. In order to eliminate the effect of altitude on pressure, it is measured at  sea level. These distributions change with season as well.

Distribution of Atmospheric Pressure

Pressure Belts of Earth

Atmospheric pressure belts envelope on the surface of the earth. They are equatorial low pressure belt, sub tropical high pressure belts, sub polar low pressure belts and polar high pressure belts

Pressure Belts of Earth

1 . Equatorial Low Pressure Belt

  • Region extending between 5° N latitude  to 5° S
  • Following are the reasons creation of low pressure belt over this region :
    1. Rays of sun fall vertically => High temperature creates low pressure.
    2. Owing to high temperature, evaporation process is also very fast => large amount of water vapours decrease the weight and density of air resulting in reduction of air pressure.
    3. Rotation of Earth and resulting centrifugal force has its maximum magnitude on Equator 
  • When air moves upward , it leads  to formation of clouds . Hence, it rains heavily in these  areas  (Cumulonimbus clouds & Convectional rainfall) . There is single  season throughout the year ie high temperature & high rainfall .
  • Advection is absent in this region because gradient of pressure is low  . Hence known as Belt of Calm / Doldrum .

2. Sub-Tropical High Pressure Belt

  • At about 30°N and 30°S latitudes on both sides of equator
  • Air which rises in equatorial region begins to cool when it reaches higher altitude over equatorial region and flows towards the poles. This wind collides with the wind coming from the polar region at higher altitude and subsides down over sub tropical latitudes. This leads to formation of high pressure belt
  • It is said that to avoid the slowing down of ship due to high pressure, the horses were thrown into the sea. So this belt is called as ‘Horse latitude’.

3. Sub Polar Low Pressure Belt

  • These are low pressure belts found at 60°N and 60°S latitudes on both sides of equator
  • The warm westerly wind from sub tropical region moves towards the pole and collide with the cold polar easterly wind from polar high pressure region and raises up to form sub polar low pressure belt.

4. Polar High Pressure Belt

  • Region at poles on both sides of equator
  • In this region, high pressure is formed because temperature remains low for whole of the year.

 Side Note : Basis of formation of pressure belts

Pressure belts can be created because of two reasons

1 . Temperature / Thermally formed

  • The Equatorial Low Pressure Belt and Polar High Pressure Belt are formed due to high and low temperature respectively. Hence, these are ‘thermally formed pressure belts’

2.  Dynamically formed

  • The Sub Tropical High and Sub Polar Low pressure belts are formed due to movement and collision of wind systems. Hence, they are called ‘Dynamically formed pressure belts’.

Temperature and Heat Budget of Earth

Temperature and Heat Budget of Earth

This article deals with ‘Temperature and Heat Budget of Earth’ This is part of our series on ‘Geography’ which is important pillar of GS-1 syllabus . For more articles , you can click here

Air Temperature

  • Air temperature of a particular place denotes the degree of hotness or coldness of air at a given place. It is generally measured in Celsius

Heating  process of Atmosphere

There are different ways of heating & cooling of the atmosphere.

  • Conduction :The air in contact with the land gets heated by conduction . Conduction is important in heating the lower layers of the atmosphere.
  • Convection : The air in contact with the earth rises vertically on heating in the form of currents and further transmits the heat of the atmosphere. This process of vertical heating of the atmosphere is known as convection. The convective transfer of energy is confined only to the troposphere.
  • Advection : The transfer of heat through horizontal movement of air is called advection.  (In northern India, during summer season local winds called ‘loo’ is the outcome of advection process).
  • Radiation (Green House effect)  : The insolation received by the earth is in short wave form and it heats up  surface. The earth after being heated itself becomes a radiating body and it radiates energy to the atmosphere in long wave form. The long wave radiation is absorbed by the atmospheric gases particularly by carbon dioxide & other Green House Gases. Thus, the atmosphere is indirectly heated by the earth’s radiation.
Green House Effect

Heat Budget of Earth

The earth as a whole does not accumulate or loose heat. It maintains its temperature. This can happen only if the amount of heat received in the form of insolation equals the amount lost by the earth through terrestrial radiation. This is known as Heat Budget of Earth

This is done in following way

Suppose 100 units are coming to earth

Heat Budget of Earth
Temperature and Heat Budget of Earth

Factors affecting  Horizontal temperature distribution

1 . Latitude of the place

  • Insolation received by any place depend upon latitude because when we move from equator towards pole, sun-rays become slanted . In slanted sun-rays, same energy is diffused over large area
  • Conclusion : Temperature decreases from the equator to the poles.

2. Distribution of Land and Water

  • Compared to land, the sea gets heated slowly and loses heat slowly. Land heats up and cools down quickly.
  • So more land mass in northern hemisphere leads to higher average temperature than the southern hemisphere

3. Presence of warm & cold current

  • Places located on the coast where the warm ocean currents flow record higher temperature than the places located on the coast where the cold currents flow.

4. Air mass circulation

  • The passage of air masses also affects the temperature. The places, which come under the influence of warm air-masses experience higher temperature and the places that come under the influence of cold airmasses experience low temperature.

5. Cloudiness

  • Cloudy  sky obstructs the solar radiation from the sun to reach earth. Hence, clear sky increases the temperature of place.
  • Due to this, Maximum insolation is received over the subtropical deserts, where the cloudiness is the least. Equator receives comparatively less insolation than the tropics because of clouds.

6. Nature of Surface

  • Albedo ie ability of surface to reflect the sunrays also impact temperature of place.
  • Fresh snow has albedo of upto 90% and  more reflection from the snow surface leads to low temperature accumulation compared to bare land.

7. Local aspects

  • Depend on position to position.

Factors affecting  vertical  temperature distribution

  • The temperature decreases with increasing altitude from the surface of the earth.
  • Reason : Atmosphere is indirectly heated by terrestrial radiation  from below. Therefore, the places near the sea-level record higher temperature than the places situated at higher elevations.
  • The vertical decrease in temperature of troposphere is called as ‘Normal Lapse Rate’ which is 6.5 C per 1000 meter of ascent.

Temperature Inversion

  • Normally , within Troposphere, temperature decreases with increase in  height . But if  reverse happens,  it is called Temperature Inversion .
  • Since cold air is denser/heavier than warm air , in case of temperature inversion, air will not be able to move upward .
temperature inversion

When Temperature Inversion can happen

  • At Tropopause :  Temperature starts to increase from here . As a result,  air  packets reach  till Tropopause & then starts moving downward . There is  no vertical air movement after that
  • A cool winter night with no clouds and stable air : Air above cold surface gets cold but layer  above cold air is still warmer & hence it cant move upward . This phenomenon is prominent till 400 m above earth’s surface.
temperature inversion
  • Valley Inversion/Air Drainage  :  In winter, mountain top becomes cold quickly compared to  valley . As a result, cold air  comes down to occupy valley . This  uplifts warm air of valley & situation is created when lower layer is cold & upper layer is warm 
valley inversion
  • Frontal inversion occurs when a cold air mass undercuts a warm air mass and lifts it 

Implications of Temperature Inversion

1 . Formation of Fog

  • As we have seen in currents ,  where ever warm & cold current meet , fog is created
  • In same way , when warm air & cold air meets , fog is created . This lowers the visibility in region.

2. Atmospheric Stability

  • Temperature Inversion prevents upward & downward movement of air.
  • Hence, it discourages rainfall.

3. Impact on Agriculture

  • Frost formed due to valley inversion damages crops in foothills, whereas trees and vegetation at top of hills and mountains are not damaged. The valley floors in the hills of Brazil are avoided for coffee cultivation because of frequent frosts.
  • (Beneficial Case : Though generally fog (caused due to temperature inversion) is unfavourable for many agricultural crops such as grams, peas, mustard plants, wheat etc. but sometimes they are also favourable for some crops such as coffee plants in Yemen hills of Arabia where fog protect coffee plants from direct strong sun’s rays. )

4. Environmental problem

  • In winters, concentration of pollutants raises to very high levels in cities as due to temperature inversion, air gets trapped . Eg : Delhi’s pollution levels are more in winters than summers.
impact of temperature inversion

Urban Heat Island

An urban heat island is an urban area or metropolitan area that is significantly warmer than its surrounding rural area due to high concentration of high rise concrete buildings, metal roads, sparse vegetation cover and less exposure of soil. These factors cause urban regions to become warmer than their rural surroundings, forming an “island” of higher temperatures.

Urban Heat Island

Composition and Structure of Atmosphere

Composition and Structure of Atmosphere

This article deals with Composition and Structure of Atmosphere’ This is part of our series on ‘Geography’ which is important pillar of GS-1 syllabus . For more articles , you can click here


  • Atmosphere is combination of two words ‘Atmo’ and ‘sphere’. It means that region of Earth which has ‘air’.
  • Atmosphere is present as life saving layer between outer space and land surface. It is the source of important gases which are important for the existence and continuity of life. It also filters the harmful rays travelling towards Earth

Composition of Atmosphere

  • Earth’s atmosphere is composed of a mixture of various gases .
  • It is held to earth by gravitational forces
  • Atmosphere is denser at sea level & thins or gets  rarefied rapidly upward . It should be noted that, 99% of the mass of atmosphere is confined to height of 32 km
  • Percentage of different gases (by volume) in atmosphere is as follows :-
Composition of Atmosphere
  • Atmospheric gases don’t interact with each other chemically & don’t lose their own property.
  • These gases can be divided into two groups based on their distribution horizontally
Permanent Gases Nitrogen , Oxygen, Hydrogen & Argon.
Their quantity remain same on all places .
Variable Gases Water Vapour , Carbon dioxide & Ozone
Their quantity vary from region to region. Eg : In coastal areas, there will be more water vapours and in cities, there will be more Carbon dioxide. 
– They can absorb heat & hence known as Green House Gases.
  • Based on vertical distribution, they can also be grouped into two groups. Heavy gases like Nitrogen , Oxygen and Methane have high composition near earths surface. While going up, composition of lighter gases keep on increasing but since there is high turbulence, no effective separation occurs in most of gases except for  two gases.
Water Vapour Near surface of earth, they are upto 2% by volume but no trace present above 10-12km.  
Ozone Found mainly between  10-50 km in stratosphere.

Side Note : Important gases in Atmosphere ( not on basis of percentage but function )

1 . Nitrogen

  • Present in atmosphere in highest proportion (78%)
  • It is very important for living organisms because it is an important element of Amino acids which form protein

2 . Oxygen

  • Second most abundant gas in atmosphere (21%)
  • All the living organisms use it for breathing

3. CO2

  • Meteorologically very important gas .
  • It is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation . Hence, it is mainly responsible for Green House effect.

4. O3

  • Ozone gas is found between 10-50 km
  • It act as filter and absorb UV rays .
  • But scientists are very concerned about the depletion of ozone layer due to action of chlorofloro carbons on Ozone

5. Water Vapour

  • Variable gas
    1. Can be upto 4% by volume in wet tropics
    2. In dry & cold areas of desert & polar deserts it can be less than 1% of air .
  • It also absorbs parts of the insolation from the sun and preserves the earth’s radiated heat.

6. Dust

  • May originate from different sources & include sea salts, fine soil, smoke-soot, ash, pollen, dust & disintegrated particles of meteors.
  • It is concentrated in lower parts , yet convectional air currents can take them to great heights .
  • They perform two very important functions
    1. It provides Hygroscopic nuclei around which water vapour condenses to produce clouds .
    2. They absorb  and reflect small amount of radiation rays of sun.

Structure of Atmosphere

Structure of Atmosphere

Atmosphere can be divided into five distinct layers   based on the thermal characteristics and temperature variations (note : these divisions are based on thermal characteristics)

1 . Troposphere

  • Troposphere is the  lowest layer of atmosphere and it is very important for all the living organisms
  • Name has been derived from Greek word ‘Tropos’ which means mixing  and ‘sphere’ which means ‘region’. Hence, ‘troposphere’ means ‘region of mixing’
  • Troposphere is zone of air turbulence because in this zone,   convectional air currents rise due to heating of earth surface
  • Thermal Characteristic of Troposphere
    1. Temperature decreases with increase in height (reaches  – 60 degree Celsius at tropopause).
    2. In normal conditions,  the rate of decrease of temperature is (ie lapse rate) is 6.5 degree Celsius per kilometre . This happens because of decrease in gases with increase in height 
    3. However, due to local reasons, at some places this phenomena reverses also (called Temperature Inversion).
  • Height of Troposphere
    1. on Equator, it is 18 km (gases are heated up and rises upward from strong convectional currents)
    2. on poles, it is 8 km (gases are cold and settles down)
    3. At average its height is upto 12 kilometre from ground.
  • All weather phenomena occur in this layer as it has dust particles and water vapour. This layer has clouds which produce precipitation on the earth.


  • It is the region between Troposphere and Stratosphere which is 1.5 kilometre high
  • The fall in temperature comes to an end in this region
  • Turbulent mixing of gases, winds, and radiation etc. none of the weather activities take place in this region

2. Stratosphere

  • Stratosphere  extends from  end of Tropopause up to a height of 50 km from the earth’s surface.
  • The lower part of this layer  is highly concentrated with ozone gas which is called as ‘ozonosphere’. It prevents the harmful ultra-violet rays from the Sun to enter into the lower part of the atmosphere
  • Thermal Characteristics of Stratosphere
    1. Temperature increases with height (ie from – 60 degree Celsius at start to 0 degree Celsius at Stratopause) .
    2. Temperature increases because of absorption of ultra violent rays by ozone gas
  • It is turbulence free zone . Hence, it is ideal for flying jet aircraft.(important prelims question)

3. Mesosphere

  • Mesosphere lies above the stratosphere, which extends up to a height of 80 km from earth’s surface .
  • Thermal characteristics of Mesosphere
    1. In this layer, once again, temperature starts decreasing with the increase in altitude
    2. From 0 degree Celsius at start, it reaches up to minus 100°C at the height of 80 km.
  • Most of the shooting stars get burned in Mesosphere .Luminous noctilucent clouds form here due to the presence of cosmic dust. ( important prelims question)
  • It is the coldest layer of earth .

4. Ionosphere /Thermosphere

  • It extends from 80 km to 400 km above Earths Surface  ..
  • It is called ionosphere due to presence of electrically charged ions that reflect radio waves back and thermosphere because it is at very high temperature.
  • Thermal characteristics of Ionosphere
    1. Temperature increases rapidly  with height  .
    2. The temperature increases rapidly up to 1,000 degree Celsius. This is due to absorption of high energy solar radiation and cosmic waves ( which break molecules to ions).
  • How Ionosphere is formed ?
    1. High energy sun rays  and cosmic rays break atoms of gases in this region .
    1. Molecules become ionised (positive charged ).
    2. These are highly energised particles & behave as free particle .
  • Luminous phenomenon called auroras at higher latitudes  when Solar Winds are able to reach ionosphere and collide with ions present in this layer  (Aurora Borealis (Arctic Zone ) & Aurora Australis(Antarctic Zone) )
  • Use of Ionosphere in radio communication : It is useful in radio communication  because ions can reflect radio waves.

5. Exosphere

  • Outermost layer of atmosphere and lies from 400 km  to 1000 km from earth’s surface.
  • This is the highest layer but very little is known about it.
  • It has rarefied contents. It contains mainly oxygen and hydrogen atoms. These atoms can travel hundreds of kilometres without colliding with one another. Hence, matter in exosphere doesn’t behave like gases.
  • It gradually merges with outer space.

Magnetosphere/ Van Allen Radiation Belt

  • Magnetosphere lies above Atmosphere and extends from 1000 km to 36000 km from earth’s surface
  • Although it isn’t  part of atmosphere but plays important part in shielding earth from solar & other cosmic winds .
  • Magnetosphere is formed due to earth’s magnetic field and it prevents most of  solar winds(highly energised particles) from reaching earth .

Polar cusps: regions above geomagnetic poles where solar wind can enter relatively easy to earth’s atmosphere.

Magnetospheric Storms

  • Magnetospheric storms are temporary disturbances in earths magnetic field  caused by occurrence of  magnetic flares & sunspot. In this process,  material from solar  coronal mass ejection  hits earth
  • Major effect in such event is global disruption of radio & telegraphic communication.


  • Luminous  phenomenon observed in high latitude regions .
  • May appear as rolling lights or coloured streaks .
  • Produced by entry of charged particles from sun into earths atmosphere  &  collision of these charged particles with ionised particles in ionosphere .  They emit energy on interaction leading to formation  of aurora.
  • Entry of these charged particles occur at Cusp . Hence, formed at particular places on earth (& not everywhere)
  • Occur in Ionosphere.
  • Most frequent during intense period / solar minimum of sun spot cycle(sun spots have cycle of 11yr).

Side Topic : Sunspot , Sunspot Cycle & Solar Minimum

  • Sun-spots are the regions on the sun where the solar magnetic field is very strong (and as a result, it doesn’t allow solar streams to escape the sun)
  • Sun-spot cycle is the solar magnetic activity cycle with the average time period of eleven years.
  • Solar minimum is the period of least solar activity in the eleven year solar cycle. During this time, sunspot activity diminishes. According to NASA and other agencies, a solar minimum is about to occur in 2020-21. 

Impact of Solar Minimum

  • During the solar minimum, coronal holes can last for a longer time. Coronal holes are vast regions in the sun’s atmosphere where the sun’s magnetic field opens up and allows streams of solar particles to escape the sun.
  • It could enhance  events of  geomagnetic storms & auroras, potentially disrupting communications and navigation systems.
  • Sun’s magnetic field weakens and provides less shielding from the cosmic rays. This can pose an increased threat to astronauts travelling through space.