🌍 ATMOSPHERE – COMPLETE SUMMARY NOTES

(Structured + Exam-Oriented)

1. 🌡️ Heating of Atmosphere

• Atmosphere is heated from below (Earth’s surface)
• Process:
  • Solar radiation → passes through atmosphere
  • Earth absorbs → re-radiates heat upward
  • Atmosphere warms from terrestrial radiation

2. ✈️ Tropopause (Very Important for Aviation)

🔹 Definition

• Boundary between:
  • Troposphere (below)
  • Stratosphere (above)

🔹 Key Characteristics

• Acts as a lid on weather
• Temperature stops decreasing here
• Marks change in lapse rate

🔹 Height Variation

🔹 Temperature

• Equator: ~ -75°C to -80°C (very cold)
• Poles: ~ -50°C

🔹 Important Facts

• Height varies with latitude
• Higher surface temp → higher tropopause
• Decreases from equator → poles
• Discontinuous near 40° & 60° latitude

🔹 Aviation Importance

• Weather confined below tropopause
• Used for:
  • Flight planning
  • Altitude selection
  • Turbulence prediction

3. 🌍 Atmospheric Layers

🟢 Troposphere

• Lowest layer
• Extends up to ~11 km
• Contains:
  • ~75% of atmospheric mass
  • Almost all weather
  • Most water vapour
• Temperature: decreases with height
• Nature: Unstable

🔵 Stratosphere

• From tropopause → 50 km
• Features:
  • Temperature increases with height (inversion)
  • Very stable
  • Contains ozone layer

Sub-features:

• Lower stratosphere → isothermal (constant temp)
• Ozone peak → 20–25 km

🟣 Mesosphere

• Extends up to ~80–90 km
• Contains:
  • Noctilucent clouds (75–90 km)

🌐 Homosphere vs Heterosphere

• Homosphere: up to ~80 km → uniform composition
• Heterosphere: above → composition varies

4. ☁️ Cloud Types (High Altitude)

• Nacreous clouds → Stratosphere (>30 km)
• Noctilucent clouds → Mesosphere (75–90 km)

5. 🌬️ Atmospheric Composition

By Volume

Ratios

• O₂ : N₂ (volume) → 1 : 4
• O₂ : N₂ (weight) → 1 : 3

6. ⚖️ Atmospheric Mass Distribution

Reason

• Due to gravity → compresses air near surface

7. 💧 Water Vapour (MOST IMPORTANT for Weather)

Key Points

• Mostly in lower troposphere
• Exists as:
  • Gas
  • Liquid
  • Solid (ice)
• Responsible for:
  • Clouds
  • Rain
  • Humidity
  • Weather formation

8. 🔥 Heat Transfer in Atmosphere

Mechanisms

Latent Heat Process

• Evaporation → absorbs heat (cooling)
• Condensation → releases heat (warming)

9. 🌱 Greenhouse Gases

Major Gases

• Water vapour (H₂O) → MOST IMPORTANT
• Carbon dioxide (CO₂)
• Methane (CH₄)
• Ozone (O₃)
• Nitrous oxide (N₂O)
• CFCs

Not Greenhouse Gas

• Oxygen (O₂)

Function

• Trap infrared radiation → warm Earth

10. 🌡️ Temperature & Lapse Rate

Standard Lapse Rate

• 6.5°C / km
• 2°C / 1000 ft

Types of Lapse Rate

Special Conditions

• Troposphere → temp decreases
• Stratosphere → temp increases (inversion)

11. 📏 ISA (International Standard Atmosphere)

Key Values

ISA Temperature Profile

12. ❄️ Oxygen & Hypoxia

• FAA recommends oxygen above 10,000 ft
• Risk: Hypoxia
  • Fatigue
  • Poor judgment
  • Unconsciousness

13. ⚡ Properties of Air

• Poor conductor of:
  • Heat
  • Electricity
• Reason:
  • Molecules far apart
  • Few free electrons

14. 🌍 Special Observations

• Above 8 km → colder over equator
• Tropopause higher in warm regions
• Stratosphere is stable → less turbulence
• Troposphere unstable → weather formation

15. 📐 Important Numerical Facts (Quick Revision)

• 50% atmosphere → below 5.5 km
• 75% atmosphere → below 10 km
• Tropopause:
  • Equator → ~16–18 km
  • Poles → ~8–10 km
• Ozone peak → ~25 km
• Lapse rate → 6.5°C/km
• Tropopause temp → -56.5°C (ISA)

✅ Ultra-Short Revision (1-Min Recap)

• Atmosphere heated from ground upward
• Troposphere:
  • Weather + unstable + temp ↓
• Stratosphere:
  • Stable + ozone + temp ↑
• Tropopause:
  • Weather limit + varies with latitude
• Water vapour:
  • Most important for weather
• Latent heat:
  • Main heat transfer (77%)
• ISA:
  • 15°C at sea level
  • -56.5°C at tropopause
• Lapse rate:
  • 6.5°C/km