atmospheric composition, structure, and radiative balance

composition of the atmosphere

78% N2, 21% O2, 0.9% Ar, 0.04% CO2, and water vapor

ppm

parts per million, what CO2 concentration is listed in (400), refers to the number of molecules of CO2 in every million molecules of dry air

pressure-altitude relationship

pressure decreases exponentially with increasing altitude → density also decreases

temperature-altitude layers

troposphere (temperature decreases with height, where weather occurs), stratosphere (temperature increases, ozone layer absorbs UV), mesosphere (temp decreases, coldest), thermosphere (temp increases, absorbs high-energy solar radiation)

Energy in = energy out, S₀(1-α) + εσT₍ₐ₎⁴ = σT₍ₛ₎⁴

Radiative Balance for Earth’s Surface, Absorbed solar radiation + back radiation from atmosphere = thermal emission from surface

Energy in = Energy out, S₀(1-α) = (1-ε)σT₍ₛ₎⁴ + εσT₍ₐ₎⁴

Radiative Balance for top of atmosphere, Absorbed solar radiation = surface radiation directly to space + atmospheric radiation to space

S₀

S/4, average solar radiation received

α

albedo, the fraction of incoming solar radiation reflected by the atm/surface

ϵ

emissivity, the fraction of infrared from the surface that is absorbed by the atmosphere

T₍ₛ₎

temperature of the Earth’s surface

T₍ₐ₎

temperature of the Earth’s atmosphere

Stefan-Boltzmann Law

all objects emit radiation according to this law where Energy flux = σT^4 in which T = temperature in K and σ = 5.67 x 10^-8 Wm^-2 K^-4

Wien’s Law

objects emit at all wavelengths; the peak wavelength depends on Wien’s law where λpeak=C/T, C = Wien’s constant = 2.898 × 10^-3 m K and T = temperature in K

insolation

incoming solar radiation that is highest at the equator where sunlight strikes most directly, decreases toward poles due to curved Earth surface causing sunlight to spread over larger areas, southern hemisphere receiving more radiation through angle of incidence

albedo

reflected solar radiation, highest over ice and snow surfaces + bright deserts/clouds, lowest over darker surfaces like forests/oceans

infrared radiation

longwave radiation that follows temperature patterns of warmer regions emitting more, highest in tropical regions and lowest in poles, affected by cloud cover and greenhouse gases that trap radiation

conduction

direct transfer of heat between two objects of different temperature

convection

movement of a fluid, such as air or water, in response to a temperature & density difference Conduction and radiation Convection

back radiation

greenhouse gases absorb outgoing infrared radiation and re-emit it in all directions, warming Earth’s surface beyond direct solar radiation

solar irradiance

amount of solar radiation received by the Earth, does not correlate with the long-term temperature trends

tropical surplus zones

the equatorial regions receive strong incoming shortwave radiation due to direct sunlight and have lower reflection, creating energy surpluses

polar deficit zones

higher latitudes receive less solar radiation due to the angle of incidence. ice and snow-covered surfaces at high latitudes have high albedo, reflecting a lot of incoming solar radiation back to space

energy transfer

heat surplus regions (tropics) transfer energy to deficit regions (poles) through atmospheric and oceanic circulation, wind patterns, currents, and weather systems

σ

Stefan-Boltzmann constant (5.67 × 10⁻⁸ W/m²K⁴)