Lecture Notes on Solar Radiation and the Atmosphere

Solar Radiation and the Atmosphere

Formation of the Universe and Earth

• Big Bang (13.8 billion years ago):
  • The universe expanded and cooled, leading to the formation of atoms, galaxies, and stars.
• Formation of Earth (4.6 billion years ago):
  • Heavy metals like iron and nickel settled to Earth's core while lighter elements formed the crust.

Structure of Earth’s Atmosphere

• Layers of the Atmosphere:
  • Thermosphere:
  • Temperature increases with altitude due to solar X-ray absorption.
  • Mesosphere:
  • Temperature decreases with altitude as air density lowers.
  • Stratosphere:
  • Temperature increases with altitude; contains the ozone layer that absorbs UV radiation.
  • Troposphere:
  • Warm air at the surface; cooler with altitude, most weather occurs here.
  • The height of the tropopause varies from the equator to the poles. Evidence exists that the tropopause shifts as the troposphere warms and the stratosphere cools.

Solar Radiation

• Importance:
  • Weather, climate, and Earth's energy balance depend heavily on solar radiation.
• Factors Influencing Solar Input (GRIDA):
  1. Influx: Amount of solar energy received by Earth.
  2. Chemical Composition: The chemical nature of the atmosphere.
  3. Albedo: Reflectivity of Earth's surfaces.

Solar Influx and Variability

• Influences on Solar Influx:
  • Variations depend on eccentricity, obliquity, and precession of Earth's orbit.
  • Solar Activity: Total solar irradiance (TSI) can vary due to:
  • Milankovitch Cycles: Long-term cycles affecting climate.
  • Solar Cycle (Sunspot Cycle):
    • Frequent changes in the number of sunspots influence solar energy output.
    • Sunspots are cooler parts of the sun's surface that can lead to solar flares and geomagnetic storms.
    • Solar maximum and minimum periods correlate with variations in solar radiation received on Earth.

Solar Flares and Geomagnetic Storms

• Interactions of solar flares with Earth's atmosphere:
  • Solar flares release energetic particles that can cause geomagnetic storms on Earth.
  • Earth's magnetic field generally protects from solar storm impacts, but intense activity can lead to auroras.

Time Scales of Insolation

• Diurnal Patterns: Daily temperature fluctuations due to solar radiation.
• Seasonal Variation: Changes in solar radiation based on Earth’s tilt and orbit, affecting climate.

Solar Constant

• The solar constant is the average amount of solar energy received outside Earth's atmosphere:
  • Calculated: $1.366 ext{ W/m}^2$ (varies seasonally from $1422 ext{ W/m}^2$ in January to $1318 ext{ W/m}^2$ in July).
  • Total for Earth: $1.740 imes 10^{17} ext{ W}$ (±3.5%).

Atmospheric Composition Changes

• Earth's Early Atmosphere:
  • Likely contained N extsubscript{2}, CO extsubscript{2}, H extsubscript{2}, CH extsubscript{4}, NH extsubscript{3}.
• Chemical processes transformed the atmosphere into its current state over time.

Radiation Attenuation

• The atmosphere modifies the quality and intensity of solar radiation by absorbing or reflecting it:
  • UV Radiation: 7%
  • Visible Light: 44%
  • Infrared Radiation: 48%
• About 50% of incoming solar radiation is either reflected or absorbed by atmospheric components, clouds, and dust.

Volcanic Effects on Climate

• Cooling Effects: Eruptions release sulfur dioxide (SO extsubscript{2}) which combines with water vapor to form aerosols that can cool the troposphere by reflecting solar radiation.
• Major eruptions can lower global temperatures significantly (e.g., the eruption of El Chichón).

Albedo and Earth’s Temperature

• Albedo: Measure of reflectivity, with a mean surface temperature of $15^{ ext{o}} ext{C}$:
  • Forest: 0.05-0.10
  • Desert: 0.13
  • Ocean: 0.07
  • Ice: -0.52 (very high reflectivity)

Circulation of Atmosphere and Oceans

• Driven by Uneven Solar Heating:
  • Creates regions of high and low pressure, generating wind patterns.
  • Coriolis Effect: Wind is deflected right in the Northern Hemisphere, left in the Southern Hemisphere.
• Circulation Patterns:
  1. Equator: Low pressure, consistent rainfall.
  2. Trade Winds: Blow from high to low-pressure areas.
  3. Horse Latitudes: Characterized by high pressure and dry conditions.
  4. Prevailing Westerlies: Affect seasons in the mid-latitudes.
  5. Polar Front: Low pressure, year-round precipitation.
  6. Polar Easterlies: High latitudes with cold air.

Latent and Sensible Heat

• Sensible Heat: Can be measured with a thermometer; associated with temperature changes.
• Latent Heat: Energy involved in changing the phase of substance (e.g., evaporation); not associated with temperature changes.
• Role in Weather Systems: Key in forming storms and atmospheric systems.

Walker Circulation and ENSO

• Walker Circulation: East-West atmospheric circulation characterized by trade winds.
• El Niño Southern Oscillation (ENSO): Predictable weather pattern disrupts normal conditions affecting global climate:
  • El Niño: Warmer sea surface temperatures leading to varied climate impacts.
  • La Niña: Cooler sea surface temperatures, restoring normal conditions.

Impacts of El Niño and La Niña

• Local Effects: Disruption in fish populations due to changes in upwelling nutrient flows.
• Global Effects: Increased rainfall and drought patterns can lead to economic impacts, natural disasters, and variability in climate patterns worldwide.

The Cryosphere

• Comprises mostly solid water (ice): glaciers, sea ice, and permafrost.
• 97% of Earth’s water is in oceans; 2.5% in glaciers, and just 1% is available for consumption.
• Monitoring melt patterns and mass balance of ice sheets to understand climate variability and change.

Current Concerns

• Ice Sheet Melting: Most melting occurs from the bottom of ice sheets rather than calving, with significant implications for sea level rise.
• Role of the Cryosphere in Climate: Changes in ice and snow cover can significantly influence global temperatures and sea levels.