Understanding Radiation Balance and Atmospheric Circulation

Infrared radiation

Infrared radiation

Energy per photon: lowest, Frequency: lowest, Wavelength: longest, 0.7-1000 μm

Ultraviolet radiation

Energy per photon: highest, Frequency: highest, Wavelength: shortest, 0.01-0.4 μm

Visible electromagnetic radiation

Energy per photon: low, Frequency: low, Wavelength: 0.4-0.7 μm

Wien's Law

λm = w / T, where λm = wavelength of maximum intensity (μm), w = Wien's constant (2897 μm K), T = absolute temperature (K)

Stefan-Boltzmann Law

F = σT^4, where F = energy emitted per unit time, per unit area (W/m^2), σ = constant [5.67*10^-8 W/m^2K^4], T = absolute temperature [K]

Earth's solar constant

1370 W/m^2

Earth's incoming solar radiation

342 W/m^2

Albedo

The amount of solar radiation being directly reflected back to space

Factors of albedo

Reflexivity of the surface, clouds, and dust

Earth's albedo

30%

Total energy absorbed by the surface

Energy absorbed = total energy captured at the surface of the atmosphere * the percentage of energy not being reflected back to space

Effective Radiating temperature

The Earth must emit the same amount of energy it absorbs from the sun (240 W/m^2), calculated using Stefan-Boltzmann's law

Greenhouse gases

Must have three or more atoms or molecules with two different types of atoms (e.g. H2O, CO2)

Non-greenhouse gases

Include O2 and N2

Greenhouse gas radiation absorption

When a GHG absorbs infrared radiation, it transitions to higher energy causing it to vibrate and/or bend, then emits radiation in a random direction

Greenhouse gases energy flow

Emit 50% of the radiation emitted by Earth back to Earth and 50% out to space

Fabs

240 W/m^2

IR surf.

480 W/m^2

Greenhouse effect

The Earth emits infrared radiation to maintain the effective radiating temperature, which is absorbed and re-emitted by greenhouse gases

Incoming radiation

Goes through the atmosphere and gets absorbed by the Earth

Equator-to-pole temperature gradient

Area closest to the poles is colder than the area near the equator due to Earth's curvature

Atmospheric circulation

Includes Polar Cells (60-90 degrees), Ferrell Cells (30-60 degrees), and Hadley Cells (0-30 degrees)

Hadley cells

Hot air rises at 0 degrees, cools down, then falls at 30 degrees

Ferrell cells

Hot air rises at 60 degrees and falls at 30 degrees

Polar cells

Hot air rises at 60 degrees and falls at 90 degrees

Surface winds direction

Predicted based on general atmospheric circulation for any latitude

Latent heat and sensible heat transfer

Other ways for energy to leave the Earth besides IR radiation, helping keep the surface cooler

Polar Easterlies

Winds that flow to the Southwest between 60 degrees North and 90 degrees North.

Westerlies

Winds that flow to the Northeast between 30 degrees North and 60 degrees North.

Northeast Trades

Winds that flow to the Southwest between 0 degrees and 30 degrees North.

Southeast Trades

Winds that flow to the Northwest between 0 degrees and 30 degrees South.

Westerlies (Southern Hemisphere)

Winds that flow to the Southeast between 30 degrees South and 60 degrees South.

Polar Easterlies (Southern Hemisphere)

Winds that flow to the Northwest between 60 degrees South and 90 degrees South.

Inter-Tropical Convergence Zone (ITCZ)

The area where trade winds meet near the equator and create a band of clouds.

Atmospheric Pressure

Higher over continents than over oceans, leading to air rising over oceans and wind moving from land to sea.

Cloud Formation

Occurs where there is low pressure.

Geostrophic Balance

A state where the Coriolis effect equals the horizontal pressure gradient force (HPGF), allowing air pockets to move along the hill.

Low Pressure Systems (Northern Hemisphere)

Flow counterclockwise.

High Pressure Systems (Northern Hemisphere)

Flow clockwise.

Low Pressure Systems (Southern Hemisphere)

Flow clockwise.

High Pressure Systems (Southern Hemisphere)

Flow counterclockwise.

Water Reservoirs

Ocean, inland seas, and saline lakes hold 97% of the total water on Earth.

Saline Groundwater

Holds less than 2% of the total water on Earth.

Fresh Water

Makes up less than 2% of the total water on Earth, most of which is locked in ice.

Residence Time

The time a water molecule spends in a reservoir, calculated as reservoir size divided by the net flux in/out.

Oceans Residence Time

3740 years.

Ekman Transport

The direction of water movement is 20-40 degrees to the right of the wind direction in the Northern Hemisphere.

Upwelling

Occurs when Ekman transport creates an area of divergence, leading to low pressure and a valley.

Downwelling

Occurs when Ekman transport creates an area of convergence, leading to high pressure and a hill.

Geostrophic Flow

The flow of ocean water that is 90 degrees to the left of the Coriolis effect in the Northern Hemisphere and 90 degrees to the right in the Southern Hemisphere.

Western Boundary Currents

Fast (up to 2m/s), narrow, deep, warm, and poleward.

Eastern Boundary Currents

Slow, broad, shallow, cool, and equator-ward.

Density Control Factors

Temperature, salinity, and pressure affect water density.

North Atlantic Deep Water (NADW)

Forms when surface water travels northwards, cools, and increases in salinity due to evaporation.

Antarctic Bottom Water (AABW)

Forms in a polynya where water loses heat and gains salt, resulting in dense water that sinks.

Deep Water Circulation

NADW sinks in the North Atlantic, travels south, and joins AABW, taking about 1000 years to complete the cycle.

Climate Modulation

Deep ocean circulation transports heat from the Southern Hemisphere to the Northern Hemisphere.