Atmospheric Pressure, Circulation, and Climate Dynamics
Air Pressure
- Definition: Force exerted by the weight of air on Earth’s surface.
- Measurement: Measured by a barometer.
- Standard: Sea-level pressure = 1013.25 mb (hPa).
Factors Affecting Air Pressure
- Temperature
- Altitude
- Water vapour
- Earth’s rotation
Pressure Belts
| Latitude | Belt |
|---|---|
| 0° | Equatorial Low (Doldrums) |
| 30° | Subtropical High (Horse Latitudes) |
| 60° | Subpolar Low |
| 90° | Polar High |
Memory Trick
0 Low → 30 High → 60 Low → 90 High
Forces Affecting Winds
- Pressure Gradient Force: High to Low
- Coriolis Force: Deflects right in the Northern Hemisphere, left in the Southern Hemisphere
- Frictional Force: Slows wind speed
Planetary Winds
- Trade Winds: 30° to 0°
- Westerlies: 30° to 60°
- Polar Easterlies: 90° to 60°
Local Winds
| Wind | Region | Nature |
|---|---|---|
| Chinook | Rockies | Warm, dry (“Snow Eater”) |
| Foehn | Alps | Warm, dry |
| Loo | North India | Hot, dry |
| Mistral | France | Cold, dry |
| Bora | Adriatic | Cold, strong |
| Sirocco | Sahara to Mediterranean | Hot, dusty |
| Harmattan | Sahara to West Africa | Hot, dusty |
| Blizzard | Polar regions | Snowstorm |
Jet Stream
- Definition: Fast upper-air winds near the tropopause.
- Speed: 100–400 km/h
- Direction: West to East
- Impact: Controls weather and the Indian monsoon.
Walker Circulation
- Definition: East-west circulation over the Pacific Ocean.
- Normal Conditions: Strong trade winds.
El Niño and La Niña
- El Niño: Unusual warming of the eastern Pacific; weakens trade winds, causing weak Indian monsoons and drought.
- La Niña: Cooling of the eastern Pacific; strengthens trade winds, usually strengthening the Indian monsoon.
Moisture and Precipitation
Evaporation and Condensation
- Evaporation: Liquid water changes into water vapour.
- Condensation: Water vapour changes into liquid droplets.
Humidity and Dew Point
- Humidity: Amount of water vapour in the air.
- Relative Humidity: Percentage of actual moisture compared to the maximum possible.
- Dew Point: Temperature at which condensation begins.
Clouds and Fog
| Type | Description |
|---|---|
| Cirrus | High, thin, feathery |
| Cumulus | White, heap-like |
| Stratus | Layered clouds |
| Nimbus | Rain-bearing clouds |
Fog: Cloud formed near the ground.
Precipitation Types
- Rain
- Snow
- Sleet
- Hail
Types of Rainfall (COC)
- Convectional Rainfall
- Orographic (Relief) Rainfall
- Cyclonic (Frontal) Rainfall
Stability and Instability
- Stable air: Resists rising.
- Unstable air: Rises and produces clouds and storms.
Climate Change and Global Warming
Weather vs. Climate
- Weather: Short-term atmospheric condition.
- Climate: Average weather over 30 years or more.
Greenhouse Effect
Atmospheric gases trap outgoing heat and warm the Earth.
Major Greenhouse Gases
- Carbon Dioxide (CO₂)
- Methane (CH₄)
- Nitrous Oxide (N₂O)
- Water Vapour
- CFCs
Global Warming
Increase in Earth’s average temperature.
Causes
- Burning fossil fuels
- Deforestation
- Industrialization
- Vehicle emissions
Effects
- Rising sea levels
- Glacier melting
- Heat waves
- Droughts and floods
- Biodiversity loss
Ozone Layer
Located in the stratosphere; absorbs ultraviolet (UV) radiation. Ozone depletion is mainly caused by CFCs.
International Agreements
- Kyoto Protocol
- Paris Agreement (keep warming well below 2°C)
Sustainable Development
Meeting present needs without harming future generations.