Key facts

  • Insolation is shortwave incoming solar energy; Earth returns longwave radiation, creating the greenhouse-effect basis.
  • Troposphere hosts most weather; stratospheric ozone absorbs ultraviolet radiation and causes temperature to rise upward.
  • Pressure belts migrate with the apparent Sun and are broken by land-sea contrast and relief.
  • Coriolis force is zero at the equator, so tropical cyclones rarely form exactly there.
  • Trade winds, westerlies and polar easterlies are planetary winds generated by pressure belts and rotation.

Key Points at a Glance

  1. 1

    Insolation is shortwave incoming solar energy; Earth returns longwave radiation, creating the greenhouse-effect basis.

  2. 2

    Troposphere hosts most weather; stratospheric ozone absorbs ultraviolet radiation and causes temperature to rise upward.

  3. 3

    Pressure belts migrate with the apparent Sun and are broken by land-sea contrast and relief.

  4. 4

    Coriolis force is zero at the equator, so tropical cyclones rarely form exactly there.

  5. 5

    Trade winds, westerlies and polar easterlies are planetary winds generated by pressure belts and rotation.

  6. 6

    Local winds such as sea breeze, valley breeze, loo and föhn arise from local thermal or terrain contrasts.

  7. 7

    Jet streams are upper-tropospheric fast winds; subtropical westerly jet helps steer western disturbances in winter.

  8. 8

    Monsoon cannot be explained by a single factor; ITCZ shift, land heating, jets and cross-equatorial flow interact.

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Scope, order and Prelims map

  • Core frame: Climatology in UPSC Prelims begins with an energy chain: Sun → insolation → unequal heating → temperature pattern → pressure pattern → winds → moisture movement → weather systems. If the first link is misunderstood, later topics such as monsoon, cyclones and western disturbances become guesswork.
  • Atmosphere first: The atmosphere is a gravitationally held envelope of gases, water vapour, aerosols and suspended particles. It is not a uniform blanket; it is layered by temperature trend, composition and function. The lowest layer, the troposphere, contains most weather because it holds most water vapour and is heated strongly from below.
  • What this note covers: composition and vertical structure; controls of insolation; horizontal and vertical temperature distribution; inversion; pressure belts; forces controlling wind; planetary winds; local winds; jet streams; and India-facing applications.
  • Prelims demand: UPSC usually tests process logic rather than isolated definitions. A common item may ask why the subtropical high exists near 30°, why tropical cyclones rarely form exactly at the equator, or why the subtropical westerly jet shifts before the monsoon.
  • Map discipline: Remember latitudinal bands with rough ranges, not rigid borders. Equatorial low, subtropical highs, subpolar lows and polar highs migrate with the apparent movement of the Sun; land-sea contrast breaks them into cells.
  • India link: Western disturbances, winter rain in northwest India, heat waves, loo, sea breeze, valley wind, inversion-linked fog and monsoon onset all depend on the same temperature-pressure-wind chain.
  • High-value trap: Weather is short-term atmospheric condition; climate is the long-term pattern. A pressure belt is a broad latitudinal tendency; a pressure cell is a more local high or low centre shown by isobars.
  • Study method: Draw one clean diagram of the three-cell circulation and annotate it with trade winds, westerlies, polar easterlies, ITCZ and jet streams. Then attach Indian examples to each mechanism.
  • Source discipline: For this foundation topic, prefer NCERT diagrams first, then standard physical geography texts. Do not import disaster-management cyclone facts into every wind question; UPSC may only be asking the basic pressure-temperature mechanism.
  • Sequence memory: Atmosphere and insolation are not separate chapters in practice. Insolation sets the thermal contrast, thermal contrast sets pressure contrast, pressure contrast starts wind, and wind redistributes heat and moisture.
  • Why diagrams matter: A single labelled circulation diagram prevents three common errors: placing deserts at the equator, treating 30° highs as cold highs, and drawing trades without Coriolis deflection.

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PredictedPredicted Questions

Use these prompts to test answer structure before moving to practice.

1MCQConsider the following statements about pressure belts: 1. Equatorial low pressure is associated with strong convection. 2. Subtropical highs are mainly produced by the descending branch of Hadley circulation. 3. Polar highs are formed because warm air rises near poles. Which statements are correct?1 marks · 50 words
  1. A1 and 2 onlyCorrect
  2. B2 and 3 only
  3. C1 and 3 only
  4. D1, 2 and 3

Explanation

Statements 1 and 2 are correct. Polar highs are linked with cold dense air subsiding, not warm air rising.

~50 words · 1 marks