4.15 sg

Chapter 15: Atmosphere, Circulation, and Climate

Overview

• The atmosphere is a complex system that consists of different layers, each playing significant roles in weather and climate.

1. Basic Concepts

• Weather: Refers to short-lived, local atmospheric conditions (temperature and precipitation) influenced by tropospheric circulation.

• Climate: Represents long-term patterns (averages over time) of temperature and precipitation.

• Composition:

  • Nitrogen gas (N2)

  • Oxygen gas (O2)

  • Water vapor (H2O)

  • Aerosols: Minute suspended particles and droplets in the atmosphere.

2. The Zones of the Atmosphere

A. Troposphere

• Location: Near Earth's surface, extends from 0 to about 18 km at the equator and 8 km at the poles.

• Characteristics:

  • Contains convection currents for heat and moisture redistribution.

  • Experiences a rapid decrease in temperature with altitude.

  • Tropopause: Boundary between the troposphere and stratosphere that limits vertical mixing.

B. Stratosphere

• Location: Extends from the tropopause to about 50 km.

• Characteristics:

  • Contains minimal water vapor but 1000 times more ozone than the troposphere.

  • Ozone layer absorbs UV light, warming this layer and protecting life on Earth.

  • Pollution Impact: Ozone depletion by substances like Freon and bromine.

C. Mesosphere

• Location: The middle atmospheric layer where temperatures again drop.

D. Thermosphere

• Location: Begins around 80 km above the Earth.

• Characteristics:

  • Made up of ionized gases at high temperatures.

  • Lower thermosphere contains ions that interact with high-energy radiation, causing the Aurora Borealis.

3. Solar Energy Absorption

• Solar energy reaching the outer atmosphere behaves as follows:

  • Reflection: 25% of solar energy is reflected by clouds and atmosphere.

  • Absorption: 25% absorbed by gases (CO2, water vapor, methane, ozone); 50% reaches the Earth's surface.

  • Certain surfaces reflect energy (e.g. water, snow).

• Albedo: Reflectivity of surfaces can vary:

  • Fresh snow: 80-85%

  • Dense clouds: 70-90%

  • Water (sun overhead): 5%

  • The average for Earth/atmosphere: 30%.

4. The Greenhouse Effect

• Mechanisms:

  • Absorption and re-emission of solar energy primarily as infrared radiation.

  • Greenhouse gases such as CO2, water vapor, and methane trap heat, supporting life.

• Anthropogenic Influences:

  • Burning fossil fuels increases CO2 levels, impacting the natural balance.

  • Deforestation reduces carbon sinks, exacerbating climate change.

5. Convection and Atmospheric Dynamics

A. Heat Transfer

• Solar energy absorption leads to the evaporation of water, storing latent heat, which is released upon condensation.

• Heat Movement:

  • Moves from equatorial regions toward the poles, redistributing warmth.

B. Pressure Systems

• Convection Currents: Result from temperature differences, creating low and high-pressure areas.

• Air moves from high to low pressure, resulting in wind and other weather patterns.

6. Weather Patterns and Phenomena

A. Coriolis Effect

• Describes the deflection of winds and currents due to Earth's rotation, leading to clockwise movement in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

B. Jet Streams

• High-altitude winds that influence weather patterns and can be affected by temperature variations.

C. Monsoons

• Seasonal wind reversals due to differential heating between oceans and continents, critical for subtropical and tropical areas.

7. Frontal Systems and Storms

A. Cold Fronts

• Formed when cooler, denser air displaces warmer air, often resulting in strong thunderstorms.

B. Warm Fronts

• Occurs when warm air glides over cooler air, leading to prolonged drizzles.

C. Cyclonic Storms

• Include hurricanes and tornadoes, driven by temperature differentials between air masses.

8. Climate Variability and Change

A. Historical Climate Changes

• Examination of ice cores reveals significant climate shifts, including the Little Ice Age beginning in the 1400s.

• Evidence shows rapid changes can occur over decades rather than centuries.

B. Milankovitch Cycles

• Important periodic changes in Earth’s orbit and axial tilt that impact solar energy distribution.

9. ENSO and Oceanic Interactions

• El Niño Southern Oscillation (ENSO): A periodic warm surface water movement between Indonesia and South America, altering global weather patterns.

• Changes affect North American weather significantly, resulting in increased storm activity during El Niño years and dryness during La Niña.