ClimatologyClimatology

The atmosphere comprises various gases, water vapor, and dust particles, layered systematically based on thermal characteristics.

• Permanent Gases: Nitrogen constitutes 78.08% and Oxygen 20.95% by volume, maintaining a relatively constant proportion up to an altitude of 80 km (Homosphere).
• Troposphere (Tropopause): Lowest layer containing 75% of atmospheric mass; temperature decreases with height at a Normal Lapse Rate of 6.4°C per 1,000 meters.
• Stratosphere (Ozonosphere): Contains the ozone layer absorbing harmful UV radiation; ideal for flying jet aircraft due to absence of weather disturbances.
• Mesosphere: Coldest layer of the atmosphere where temperatures drop to -90°C at the mesopause; meteors burn up upon entering this layer.
• Thermosphere (Ionosphere): Characterized by electrical charged ions reflecting radio waves back to Earth; includes the exosphere merging into outer space.

The earth receives energy from the sun in short wavelengths and radiates it back into space as long-wave terrestrial radiation.

• Solar Constant: The amount of solar energy received per unit area at the outer edge of the atmosphere, approximately 2 calories per sq cm per minute.
• Albedo: The reflected fraction of solar radiation by a surface; fresh snow has the highest albedo (70-90%), while forests have very low albedo.
• Earth's Heat Balance: Out of 100 units of incoming solar radiation, 35 units are reflected back (Albedo), 14 absorbed by atmosphere, and 51 reach the earth's surface.
• Greenhouse Effect: Absorption of long-wave terrestrial radiation by atmospheric gases like CO2, methane, water vapor, keeping the lower atmosphere warm.

Global atmospheric pressure distribution creates distinct pressure belts, driving planetary wind systems and ocean currents.

• Equatorial Low Pressure (Doldrums): Thermally induced low-pressure belt near the equator characterized by calm conditions, ascending air, and high convectional rainfall.
• Subtropical High Pressure (Horse Latitudes): Dynamically induced high-pressure belt around 30°-35° N/S latitudes, characterized by descending dry air and clear skies.
• Coriolis Force: An apparent force caused by earth's rotation; deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere (Ferrel's Law).
• Trade Winds and Westerlies: Trade winds blow from Subtropical High to Equatorial Low; Westerlies blow from Subtropical High to Sub-polar Low, steering mid-latitude weather.

India has a tropical monsoon climate heavily influenced by seasonal reversal of wind directions and upper tropospheric jet streams.

• Thermal Concept (Halley's Theory): Differential heating of the Asian landmass and the Indian Ocean creates high pressure over the ocean in summer and low pressure over land.
• Jet Stream Theory: The northward shift of the Sub-Tropical Westerly Jet (STWJ) and establishment of the Tropical Easterly Jet (TEJ) trigger the onset of the southwest monsoon.
• El Niño Southern Oscillation (ENSO): Periodic warming of surface waters in the eastern Pacific (El Niño) suppresses Indian monsoon rainfall, while La Niña enhances it.
• Indian Ocean Dipole (IOD): Difference in sea surface temperature between western and eastern Indian Ocean; a positive IOD is favorable for Indian monsoon rainfall.