Meteorology Lec 2a - Energy in the Atmosphere

Energy

Capacity to do work; exists as kinetic or potential forms

Kinetic Energy (KE)

Energy of motion; ½mv²

Potential Energy (PE)

Stored energy; gravitational PE mgh

Internal Energy

Sum of all KE and PE within a system

First Law of Thermodynamics

Energy cannot be created/destroyed, only converted (Conservation of Energy)

Temperature

Measure of average molecular kinetic energy

Heat

Energy transferred due to temperature differences

Absolute Zero

0 K (-273.15°C); complete absence of thermal motion

Kelvin Scale

Absolute scale (0K is absolute zero); K

Celsius Scale

Freezing at 0°C, boiling at 100°C (sea level)

Fahrenheit Scale

Freezing at 32°F, boiling at 212°F

Specific Heat

Energy to raise 1g of substance by 1°C (water 1 cal/g°C)

Latent Heat

Energy absorbed/released during phase changes (no temp change)

Conduction

Heat transfer through molecular collisions (solids > liquids > gases)

Thermal Conductivity

Ability to conduct heat (air

0.023 W/m°C; silver

Convection

Heat transfer via fluid motion (e.g., rising warm air)

Advection

Horizontal transfer of air properties (e.g., warm air mass movement)

Radiation

Energy transfer via EM waves (no medium required; speed of light)

Wien's Law

Hotter objects emit shorter wavelengths (λ_max ∝ 1/T)

Stefan-Boltzmann Law

Hotter objects emit more total energy (E ∝ T⁴)

Shortwave Radiation

Solar radiation (peak at visible/UV wavelengths)

Longwave Radiation

Earth's emitted IR radiation

Blackbody

Perfect absorber/emitter of all radiation (Earth ≈ blackbody)

Selective Absorbers

Gases that absorb specific wavelengths (H₂O, CO₂ absorb IR)

Atmospheric Greenhouse Effect

Warming from IR absorption by greenhouse gases

Radiative Equilibrium Temp

Earth's theoretical temp (255 K) without atmosphere

Actual Surface Temp

288 K (15°C); difference due to greenhouse effect

Evaporation

Cooling process (energy absorbed to change liquid → vapor)

Condensation

Warming process (energy released when vapor → liquid)

Latent Heat of Vaporization (Lᵥ)

2.5×10⁶ J/kg (energy for liquid ↔ vapor)

Latent Heat of Fusion (Lᶠ)

3.34×10⁵ J/kg (energy for ice ↔ liquid)

Water's High Specific Heat

Moderates climate (stores/releases energy slowly)

Albedo

Surface reflectivity (fresh snow 75-95%; forests 70%)

Scattering

Deflection of light by small particles (e.g., blue sky from Rayleigh scattering)

Reflection

Backward deflection of light (contributes to albedo)

Earth's Energy Balance

30% reflected, 19% absorbed by atmosphere, 51% absorbed by surface

Greenhouse Gases

H₂O, CO₂, CH₄, N₂O, CFCs (absorb/emit IR radiation)

Enhanced Greenhouse Effect

Additional warming from increased greenhouse gas concentrations

UV-C

0.20-0.29 µm; blocked by ozone layer

UV-B

0.29-0.32 µm; causes sunburns/skin cancer

UV-A

0.32-0.40 µm; causes tanning (similar cancer risk to UV-B)

Specific Heat of Air

0.24 cal/g°C (1005 J/kg°C)

Specific Heat of Water

1.00 cal/g°C (4186 J/kg°C)

Earth's Albedo

30% (average reflectivity)

Solar Constant

~1361 W/m² (incoming solar energy at top of atmosphere