UPSC Prelims 2020 Important Topics: Climatology, Atmosphere, Pressure & Temperature systems, Rainfall

UPSC Prelims 2020 Important Topics: Climatology, Atmosphere, Pressure & Temperature systems, Rainfall and Climatic regions of the world.

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It refers to the physical state of the atmosphere within 24 hours, described by weather elements such as temperature, atmospheric Pressure, humidity, rainfall, cloudiness, wind speed and wind direction.


  • The India Meteorological Department (IMD) is an agency of the Ministry of Earth Sciences of the Government of India. It is the principal agency responsible for meteorological observations, weather forecasting and seismology. IMD is headquartered in New Delhi and operates hundreds of observation stations across India and Antarctica.
  • IMD is also one of the six Regional Specialised Meteorological Centres of the World Meteorological Organization. It has the responsibility for forecasting, naming and distribution of warnings for tropical cyclones in the Northern Indian Ocean region, including the Malacca Straits, the Bay of Bengal, the Arabian Sea and the Persian Gulf


  • It is commonly defined as the weather averaged over a long period of time and over a large area.
  • The Standard averaging period is 30 years
  • The world climate is derived from the ancient Greek world ‘Klima’ which means ‘inclination’.
  • It is measured by assessing the patterns of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over periods of time.
  • A region’s climate is generated by the climate system, which has five components: Atmosphere, Hydrosphere, Cryosphere, Lithosphere and biosphere.


The Cryosphere is those portions of Earth’s surface where water is in solid form, including Sea ice, Lake ice, River ice, Snow cover, Glaciers, Ice caps, Ice sheets and frozen ground (which includes permafrost)


I. Latitude

  • The equator received vertical sunrays which fall over a smaller area
  • In contrast, the Polar Regions receive slanting sunrays and they fall over a wider area.
  • As a result of this, the places near the equator are hotter than the poles.

II. Altitude

  • The places located on higher altitudes are always cooler than those on the plains. This is because the air becomes thinner and they absorb only less heat.
  • Secondly the atmosphere can be heated upwards only from the Earth’s surface.
  • The air near the surface of the earth is denser and contains more carbon dioxide, water vapour, dust and other impurities. Hence it absorbs more heat than the thin and clear air in the upper layers.

Normal Lapse Rate:

Temperature decreases at the rate 6.50C for every 1000 metres high on the earth’s surface, this is known as Normal Lapse Rate.

III. Distance from the Sea:

  • Due to the phenomena of land and sea breezes the temperature of the coastal margins is comparatively cooler than that of a place situated far away from the sea.

IV. Oceanic Currents:

Warm ocean currents make coastal areas warm, wet and free from ice and cold currents make them cool, dry and to have ice bags.
It is classified as
1. warm ocean currents
2. Cold Ocean

Currents Oceanic Currents:

It is a continuous movement of ocean water from one place to another. There are created by wind, water temp, salt content and the gravity of the moon.

V. Direction of Prevailing winds:

  • The winds that blow from the sea contain more moisture so they are cell and wet cause rainfall. E.g. South west Monsoon.
  • The winds that blow from the land areas are warm and dry and hence there is no Rainfall. E.g. North east Monsoon.

VI. Human Influence

  • Deforestation and human development effects are felt in the name of Global warming, Greenhouse effect, and pollution, which have increased the amount of CO2
  • Creation of urban heat island. It occurs in metropolitan areas which are significantly warmer than their surrounding areas.

Elements of Weather and Climate:

The main elements of atmosphere which are subject to change and which influence human life on earth are temperature, pressure, winds, humidity, clouds and precipitation.

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