Atmosphere & Weather
Geography · वायुमंडल और मौसम
📋Quick Overview
Earth's atmosphere is a layer of gases surrounding the planet, held by gravity. It is composed mainly of Nitrogen (78%) and Oxygen (21%), with trace gases like Argon (0.93%) and Carbon Dioxide (0.04%). The atmosphere has 5 layers from bottom to top: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. Weather occurs in the troposphere, while the ozone layer is in the stratosphere.
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Weather = short-term atmospheric conditions at a place (hours/days). Climate = average weather pattern of a place over 30+ years.
📖5 Layers of Atmosphere
| Layer | Height | Temperature | Key Facts |
|---|---|---|---|
| Troposphere | 0–12 km | Decreases with height (6.5°C/km) | ALL weather occurs here, densest layer, contains 75% of atmospheric mass, clouds form here |
| Stratosphere | 12–50 km | Increases with height (due to ozone) | Ozone layer (20–35 km) absorbs UV rays, aircraft fly here (stable), no weather |
| Mesosphere | 50–80 km | Decreases sharply (-90°C at top) | Coldest layer, meteors burn here (shooting stars) |
| Thermosphere | 80–700 km | Increases greatly (up to 2,000°C) | Ionosphere is part of it (reflects radio waves), Aurora occurs here, ISS orbits here |
| Exosphere | 700–10,000 km | Very high but sparse | Outermost layer, merges with space, satellites orbit here |
📝Pressure Belts
| Pressure Belt | Location | Type |
|---|---|---|
| Equatorial Low Pressure (Doldrums/ITCZ) | 0°–5° N/S | Low pressure — hot air rises, heavy rainfall, calm winds |
| Subtropical High Pressure (Horse Latitudes) | 25°–35° N/S | High pressure — descending air, dry conditions, deserts formed here |
| Subpolar Low Pressure | 60°–65° N/S | Low pressure — warm and cold air meet, frontal rainfall |
| Polar High Pressure | 85°–90° N/S | High pressure — extremely cold, descending dry air |
📝Wind Systems
| Wind | Zone | Direction |
|---|---|---|
| Trade Winds | 0°–30° | NE in Northern Hemisphere, SE in Southern Hemisphere — most constant winds on Earth |
| Westerlies | 30°–60° | SW in NH, NW in SH — bring rainfall to western coasts of continents |
| Polar Easterlies | 60°–90° | NE in NH, SE in SH — cold and dry winds |
- •Jet Streams are high-altitude (9–12 km) fast-flowing narrow air currents in the upper troposphere. They move west to east and influence weather patterns, especially the Indian monsoon.
📖Cyclones — Tropical vs Temperate
📝Humidity & Precipitation Types
- •Humidity = amount of water vapor in the air. Relative Humidity = actual moisture / capacity x 100%
- •Convectional Rainfall — caused by heating of ground, air rises and cools (common in equatorial regions, afternoon thunderstorms)
- •Orographic/Relief Rainfall — moist wind hits a mountain, rises, cools and rains on windward side. Leeward side = rain shadow (dry)
- •Frontal/Cyclonic Rainfall — warm and cold air masses meet, warm air rises over cold air (common in temperate regions)