1. Temperature and Pressure Belts of the World

Temperature Belts

  • The Earth receives uneven solar radiation due to its spherical shape, leading to the formation of temperature zones.
  • These zones are roughly:
    • Torrid Zone (between Tropic of Cancer and Tropic of Capricorn)
    • Temperate Zones (between tropics and polar circles)
    • Frigid Zones (beyond polar circles)
  • Insolation (incoming solar radiation) is highest at the equator and decreases toward the poles.
  • The angle of incidence of the sun’s rays is a major factor in determining the temperature distribution.
  • The land-sea contrast, ocean currents, altitude, and winds cause deviations in the actual temperature belts.

Pressure Belts

  • The Earth’s surface is divided into seven major pressure belts:
    • Equatorial Low (0°)
    • Subtropical Highs (~30°N and S)
    • Subpolar Lows (~60°N and S)
    • Polar Highs (90°N and S)
  • These belts form due to thermal and dynamic factors:
    • Equatorial low pressure is thermally induced due to intense heating and rising air.
    • Subtropical high is dynamically induced due to descending air from Hadley Cells.
    • Subpolar low is a result of converging air from Ferrel and Polar cells.
    • Polar high is thermally induced due to cold, dense air.
  • The belts are not fixed and shift north and south with the apparent movement of the sun.

2. Heat Budget of the Earth

  • The heat budget refers to the balance between incoming solar radiation and outgoing terrestrial radiation.

Key Components:

  • Incoming Solar Radiation (Insolation): Only about 51% reaches Earth’s surface; the rest is absorbed or reflected.
  • Reflected Radiation (Albedo): Roughly 30% of the total insolation is reflected back into space by clouds, aerosols, land, and oceans.
  • Absorbed Radiation:
    • Surface absorbs ~51%
    • Atmosphere absorbs ~19% (mostly by water vapor, ozone, etc.)
  • Outgoing Radiation:
    • The Earth’s surface emits longwave radiation (infrared) into the atmosphere.
    • Some is absorbed and re-emitted by greenhouse gases (CO₂, CH₄, H₂O vapor), warming the Earth through the greenhouse effect.
  • A balance is maintained over the long term, but local and short-term variations cause weather changes.

3. Atmospheric Circulation

  • Driven by pressure differences and the Coriolis force, the atmosphere circulates to maintain heat balance.

Global Circulation Cells:

  1. Hadley Cell: Warm air rises at the equator, travels poleward at high altitude, and descends around 30° latitude.
  2. Ferrel Cell: Lies between 30° and 60° latitude. Air flows poleward at the surface and equatorward at high altitude.
  3. Polar Cell: Cold air sinks at poles and moves towards 60° latitude at the surface.

Major Wind Systems:

  • Trade Winds: Blow from subtropical highs towards equatorial low (NE in Northern Hemisphere, SE in Southern Hemisphere).
  • Westerlies: Blow from subtropical highs to subpolar lows (SW in NH, NW in SH).
  • Polar Easterlies: Flow from polar highs to subpolar lows.

Seasonal Shifts:

  • The Inter-Tropical Convergence Zone (ITCZ) shifts with the sun, influencing monsoon and tropical climates.
  • Jet Streams, narrow bands of strong winds in the upper atmosphere, also impact circulation patterns.

4. Atmospheric Stability and Instability

Atmospheric Stability:

  • The atmosphere is stable when a displaced air parcel returns to its original position.
  • This occurs when the environmental lapse rate is less than the adiabatic lapse rate.
  • In such cases, vertical motion is suppressed, leading to clear skies and stable weather conditions.

Atmospheric Instability:

  • The atmosphere is unstable when a displaced air parcel continues to rise.
  • This happens when the environmental lapse rate is greater than the adiabatic lapse rate.
  • Promotes vertical air movement, cloud formation, and convective precipitation (common in tropical regions).

Types of Stability Conditions:

  • Absolutely Stable: ELR < SALR < DALR (no vertical movement).
  • Absolutely Unstable: ELR > DALR > SALR (intense vertical movement).
  • Conditionally Unstable: DALR > ELR > SALR (instability depends on air saturation).

Relevance:

  • Understanding stability is crucial for forecasting thunderstorms, fog, inversions, and air pollution dispersion.

Published by Pragyanxetu

One Earth. One Future

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