Contested Planet: Atmosphere and Weather Systems Notes

Atmosphere and Weather Systems

• Focuses on the atmosphere, climate zones, and weather systems.
• Examines atmospheric characteristics and air movement.
• Discusses hazardous weather impacts on human populations and management strategies.

Weather vs. Climate

• Weather: Short-term atmospheric conditions (hours/days).
  • Includes temperature, humidity, precipitation, wind, and pressure.
  • Highly variable.
• Climate: Long-term weather patterns (decades/centuries).
  • Includes average temperature, precipitation, and wind patterns.
  • Influenced by latitude, altitude, ocean currents, and topography.
  • Changes slowly, more predictable.

Factors Affecting Climate

• Latitude: Temperatures decrease further from the equator.
  • Sunlight has more atmosphere to pass through, lower angle of sun, more energy reflected by ice/snow.
• Altitude: Temperatures decrease with height.
  • Temperature drops $0.6°C$ per 100 meters.
  • Air is thinner at higher altitudes.
• Distance from Sea: Oceans heat/cool slower than land.
  • Coastal areas are cooler in summer/warmer in winter than inland areas.

Composition of the Atmosphere

• Air surrounding the earth, mixture of gases held by Earth's gravity.
• Contains oxygen for humans/animals and carbon dioxide for plants.
• Stops harmful UV rays and maintains suitable temperature.
• Extends up to 1600 km, but 99% of mass is within 32 km.

Atmospheric Gases

• Nitrogen and oxygen make up 99% of the atmosphere.
• Other gases: argon, carbon dioxide, neon, helium, hydrogen.
• Oxygen decreases at heights above 120 km.
• Carbon dioxide and water vapor are found up to 90 km.

Carbon Dioxide

• Transparent to incoming solar radiation but opaque to outgoing terrestrial radiation.
• Absorbs terrestrial radiation and reflects some back, causing the greenhouse effect.
• Increasing CO2 from fossil fuels is the main reason for global warming.

Ozone Gas

• Found between 10-50 km above Earth’s surface.
• Absorbs ultraviolet rays from the sun.
• Limited to the ozone layer in the stratosphere.

Water Vapour

• Gaseous form of water, source of precipitation.
• Decreases with altitude and from equator to poles.
• Maximum amount is 4% in warm, wet regions.
• Reaches the atmosphere through evaporation and transpiration.
• Absorbs solar radiation and preserves Earth's radiated heat, acting like a blanket.

Dust Particles

• Found in lower layers of the atmosphere (sand, smoke, salt, pollen).
• Higher concentration in subtropical/temperate regions.
• Help in condensation of water vapor, forming clouds.

Structure of the Atmosphere

• Five layers based on temperature and density:
  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere (Ionosphere)
  • Exosphere

Troposphere

• Lowermost layer, 18 km at equator, 8 km at poles.
• Thickness greatest at the equator due to convection currents.
• Contains dust particles and water vapor.
• Most weather changes occur here.
• Temperature decreases with height: Normal Lapse Rate (1°C per 165 m).
• Separated from stratosphere by tropopause.

Stratosphere

• Above troposphere, extending up to 50 km.
• Temperature constant in lower part, then increases with height due to ozone.
• Ideal for flying aircraft, as weather incidents don't take place here and air flows horizontally.
• Upper limit known as stratopause.
• Contains ozone layer that absorbs UV radiation.

Thermosphere (Ionosphere)

• Located between 80 and 400 km above the mesopause.
• Contains ions, reflecting radio waves back to earth.
• Temperature increases with height.

Exosphere

• Uppermost layer of the atmosphere.
• Gases are sparse due to lack of gravity, low air density.
• Transition zone to outer space.

Global Atmospheric Circulation

• Air moves due to temperature differences between the equator (warm) and the poles (cold).
• Pressure measured in millibars; standard pressure at sea level is 1013 millibars.
• Rising warm air causes low pressure; sinking cool air causes high pressure.
• Equator: high temperatures, rising air, low pressure, condensation, rainfall (tropical rainforests).
• 30° N/S: sinking air, high pressure, dry conditions, few clouds (deserts).

Tricellular Model

• Provides framework for understanding atmospheric circulation.
• Emphasizes vertical and latitudinal movement of air masses.
• Explains global temperature, precipitation, and vegetation distribution.

Hadley Cell

• Located near the equator, characterized by rising warm air and low pressure.
• Air rises, cools, condenses, and forms clouds/rain.
• Air moves poleward, descends around 30° latitude creating high-pressure zones.
• Responsible for ITCZ and distribution of tropical rainforests/deserts.

Ferrell Cell

• Located between 30° and 60° latitude in both hemispheres.
• Dominated by prevailing westerly winds.
• Air masses converge, leading to mid-latitude cyclones.
• Characterized by variable weather with temperate forests and grasslands.

Polar Cell

• Located near the poles, characterized by sinking cold air and high pressure.
• Sinking air flows towards lower latitudes, forming polar easterlies.
• Transports cold air to mid-latitudes, contributing to polar deserts/tundra.

Earth’s Heat Budget

• Balance between incoming solar radiation and outgoing terrestrial radiation.
• Influenced by surface properties, atmospheric composition, circulation patterns.
• Solar Radiation: Primary energy source; varies by time, season, latitude.
• Albedo: Reflectivity of a surface (high: ice/snow; low: forests/oceans).
• Atmospheric Absorption/Scattering: Gases absorb/scatter solar radiation.
• Outgoing Radiation: Earth emits longwave radiation; influenced by temperature.
• Heat Storage: Surface/atmosphere store/redistribute heat.

World Distribution of Atmospheric Pressure

• Pressure belts oscillate with the apparent movement of the sun.
• Equatorial Low: Near the equator; low pressure.
• Subtropical High: Along 30° N/S; high pressure areas.
• Sub-polar Lows: Along 60° N/S; low pressure belts.
• Polar Highs: Near poles; high pressure.

Precipitation Types

• Rain: Liquid water droplets.
• Snow: Ice crystals.
• Sleet: Small ice pellets.
• Hail: Large ice pellets formed in thunderstorm clouds.

Formation of Precipitation

• Condensation: Water vapor condenses onto condensation nuclei.
• Deposition: Water vapor directly changes into ice.

Relief (Orographic) Rainfall

• Moist air rises over elevated terrain, cools, and condenses on windward side.
• Leeward side experiences rain shadow effect (drier conditions).

Frontal (Cyclonic) Rainfall

• Occurs at boundaries between air masses.
• Warm air rises over colder air, forming clouds and precipitation along the front.
• Warm Front: Widespread, prolonged rainfall as warm air rises over a retreating cold air mass.
• Cold Front: Intense, short-lived showers as cold air forces warm air to rise rapidly.

Convectional Rainfall

• Sun heats Earth's surface, causing air to rise rapidly.
• Rising air cools, condenses, and forms cumulus clouds, leading to showers/thunderstorms.
• Common in tropical regions with high temperatures and moisture.

Air Masses

• Equatorial: Warm, moist, unstable; move towards poles.
• Tropical: Warm, dry, stable; move towards higher latitudes.
• Polar: Cold, dry, stable; move towards lower latitudes.
• Arctic: Exceptionally cold, dry, stable; move towards lower latitudes during winter.

Seasonal Variations in Global Circulation

• Changes in atmospheric circulation due to Earth's tilt and orbit around the Sun.
• Tilt of the Earth Leads to variations in solar radiation which drives pressure belts movement.
• ITCZ shifts with the seasons.
• Jet Stream and Rossby Waves affect Mid-latitude weather.

Role of Jet Stream

• High-speed air current in upper atmosphere.
  • Polar Jet Stream: Temperature Gradient between the polar and mid-latitude air.
  • Subtropical Jet Stream: Temperature Gradient between the mid-latitude and the tropical air.
• Affects weather patterns by steering storms and influencing air mass movement.