Solar Radiation and Climate

Chapter 2: Solar Radiation and Climate

I. Important Concepts

• Climate:

  • Defined as the average weather conditions in a region over the year(s), encompassing temperature, moisture, precipitation, and winds.

  • Holds substantial ecological significance by influencing various natural processes and life forms.

II. Factors that Affect Climate

1. Solar Radiation:

   • Serves as the key factor influencing climate.

   • Solar Constant:

     • The amount of solar radiation that reaches a point (83 km) on a surface that is perpendicular to the sun’s rays.

A. Fate of Solar Radiation

• Of the incoming solar radiation:

  • 50% is reflected by the atmosphere.

    • Of this 50%, 30% is reflected into space, and 25% is absorbed by atmospheric components like dust, water vapour, and CO₂.

    • Out of this absorption, 12% is reflected back to space, while 88% is reradiated back to Earth.

  • 45% is absorbed by Earth’s surface.

B. Incoming Solar Radiation Example

• Total incoming solar radiation: 100%

  • Reflected solar radiation: 30%, detailed as follows:

  • Reflected by the atmosphere: 29%

  • Reflected by the surface: 5%

  • Absorbed by the atmosphere: 25%

  • Absorbed by the surface: 45%

  • Emitted longwave radiation: 66%

C. Net Radiation Equation

• Net Radiation:

  • Defined as:
    $ext{Net Radiation} = ( ext{Incoming SW} - ext{Reflected SW}) - ( ext{Emitted LW} - ext{Downward LW})$

D. Skylight Composition

• Most ultraviolet radiation is filtered out by atmospheric gases.

• Shorter wavelengths are scattered, resulting in a blue sky effect, while dust scatters longer wavelengths resulting in red and yellow skies.

• Water vapor from clouds scatters all wavelengths, leading to a white cloudy sky.

E. Albedo

• Defined as the percentage of incoming solar radiation that is reflected from the surface back into space.

• Albedo of various surfaces:

  • Water:

  • Direct overhead rays yield low albedo: 2%

  • Low angle rays yield high albedo.

  • Snow/Ice:

  • High albedo: 45-90%

  • Forests and Grasslands: 5-30%

  • Clouds: 90%

F. Importance of Humidity

• Defined as the maximum amount of water vapor that air can contain, which is dependent on temperature.

• Dew Point:

  • Temperature at which moisture content in the air saturates, leading to the formation of condensation.

G. Adiabatic Process

• No heat is lost or gained from the outside environment.

• Occurs when a column of air warms, rises, or expands, and subsequently cools with no energy loss.

III. Influence of Earth's Rotation on Climate

1. Coriolis Force:

   • The effect caused by the Earth’s rotation, influencing the direction of winds and ocean currents.

   • In the atmosphere, it primarily affects prevailing winds and storm rotations.

IV. Movement of Air Masses

1. Heating near the Equator:

   • Air at the equator heats, causing it to rise and spread towards the North and South poles.

2. Effects of Earth's Rotation:

   • Generates the Coriolis effect, deflecting winds into distinct patterns based on latitude.

     • Polar easterlies, westerlies, and trade winds are all impacted by this deflection:

     • Tropical (Hadley Cell), Mid-latitude (Ferrel Cell), and Polar Cells illustrated.

V. Ocean Currents

1. Play a crucial role in the global transfer of heat.

2. Upwellings:

   • The process by which cold, nutrient-rich water rises to the surface, supporting diverse marine life and increasing phytoplankton production.

3. Thermohaline Circulation:

   • Describes the movement of ocean currents driven by differences in temperature and salinity, which impacts global climate patterns.

VI. Topographical Influences

1. Mountains:

   • Exhibit temperature changes with altitude and can create rain shadows via adiabatic processes.

VII. Microclimates

• Defined as climate variations on very local scales influenced by topographical features and vegetation.

1. Example:

   • North/South Facing Slopes:

     • South-facing slopes receive more solar energy; hence, they experience:

     • Higher temperatures, high evapo-transpiration, lower soil moisture, which affects local vegetation types.

     • North-facing slopes are cooler and more humid, making them preferable for certain species like salamanders.

VIII. Reality of Climate Change

1. Irregular Climate Variation:

   • Occurs at regional and larger scales due to stochastic and natural variability, exemplified by the Little Ice Age.

2. Causes of Climate Change:

   • Variable sun output, volcanic activities, thermohaline circulation disruptions, and large-scale population dynamics that lead to ecosystem changes (e.g., after the Black Death).

3. Human-Induced Climate Change:

   • Rapid increases in greenhouse gases (CO₂, CH₄, N₂O, and fluorinated gases) resulting from industrial activities.

   • A remarkable temperature increase since the early 1900s, with recent years featuring the warmest recorded temperatures.

IX. Historical Climate Patterns

• References to historical climate swings, notably during the Holocene period, including warm and cold periods with significant ecological and cultural impacts.

Figures and Illustrations (Referenced)

• Multiple figures and graphs referenced throughout the notes, illustrating concepts such as net radiation, solar visibility spectrum, temperature changes, and migration patterns associated with climate changes, although not quoted in detail here for brevity.