Insolation & Temperature Notes (Hess Ch. 4)

The Sun is the ultimate energy source for Earth’s weather and climate.
Energy travels as electromagnetic radiation (EMR):
- Shortwave radiation (UV, visible light, some infrared) from the Sun.
- Longwave radiation (infrared/heat) emitted back from Earth.
Atmosphere is largely transparent to visible light but absorbs some UV and IR.

Radiation – Transfer of energy by EM waves (e.g., Sun → Earth).
Absorption – Atmosphere or surface absorbs radiation, converting it to heat.
Reflection – Radiation bounces back without absorption (e.g., clouds, ice).
Scattering – Radiation deflected in many directions (sky looks blue).
Transmission – Radiation passes through atmosphere (e.g., visible light).
Conduction – Heat transfer through direct contact (molecules → molecules).
Convection – Heat transfer by rising warm air and sinking cool air.
Advection – Horizontal transfer of heat by wind (e.g., sea breeze).
Adiabatic Cooling/Warming – Temperature change due to air expansion (cooling as it rises) or compression (warming as it sinks), without heat exchange.
Latent Heat – Energy absorbed/released during phase changes of water (melting, evaporation, condensation).

Certain gases (CO₂, CH₄, H₂O vapor) absorb Earth’s longwave IR radiation and re-radiate it back.
This traps heat and keeps Earth warmer than it would be (~33°C warmer).
Natural and necessary for life, but human activities have enhanced the effect → global warming.

Latitude:
- Equator → receives most direct, concentrated sunlight.
- Poles → sunlight spreads over larger area, lower angle, less energy.
Season:
- Caused by Earth’s axial tilt (23.5°), not distance from Sun.
- Summer hemisphere → more direct rays, longer days.
- Winter hemisphere → less direct rays, shorter days.
Atmosphere modifies insolation through absorption, reflection, scattering, reducing surface energy.

Specific heat = energy required to raise temperature of a substance.
- Water has high specific heat → heats/cools slowly.
- Land has low specific heat → heats/cools quickly.
Other factors:
- Water is transparent (heat distributed through depth).
- Mixing of water spreads heat.
- Evaporation cools water surfaces.
Implications for climate:
- Continental climates (inland): Larger temperature swings, hotter summers, colder winters.
- Maritime climates (coastal): Milder, smaller annual temperature range.

Insolation – Incoming solar radiation received at Earth’s surface.
Greenhouse Gases – Atmospheric gases (CO₂, H₂O vapor, CH₄) that trap heat.
Latent Heat – Energy absorbed/released during phase changes of water without changing temperature.
Albedo – Reflectivity of a surface (high for ice/snow, low for dark soil/ocean).

How the Sun’s radiation powers Earth’s climate system.
The 10 heat transfer processes in the atmosphere.
The greenhouse effect.
Why insolation varies by latitude and season.
Why land and water heat differently (and how this affects climate).
Real-world relevance:
- The greenhouse effect is natural and necessary for life-supporting temperatures, but human activities have enhanced it, contributing to global warming.
- Land–water contrasts help explain coastal vs inland climate differences and seasonal cycles.
Ethical and practical implications:
- Emissions reductions and climate policies influence future warming and regional climates.

Axial tilt (obliquity) of Earth:
- $\delta = 23.5^{\circ}$
Global warming magnitude associated with the enhanced greenhouse effect:
- $\Delta T \approx 33^{\circ}\mathrm{C}$
Sensible heat transfer (general):
- $Q = m c \Delta T$
Latent heat transfer (phase change):
- $Q = m L$
Albedo and absorbed radiation relationships:
- Reflectivity: $\alpha = \frac{R<em>{\text{reflected}}}{R</em>{\text{incident}}}$
- Absorbed solar radiation: $R<em>{\text{absorbed}} = (1-\alpha) R</em>{\text{incident}}$