Earth’s Climate System (part 2)

• revisiting the radiation budget • heat capacity• heat transfer• circulation of atmosphere (winds)• Coriolis Effect• circulation of oceans (currents)

Earth’s climate system

• climate driven by “solar energy”

• climate operates to distribute solar energyacross surface

From last time:

Revisiting the radiation budget

energy in = energy used for warming+ energy radiated back to space

Unequal distribution across Earth

Energy input & output averaged over year

Earth’s spin axis is inclined, so we get seasons

23.5o

Energy input by latitude & month

Radiation budget

energy in = energy used for warming+ energy radiated back to space

Energy transferred to Earth:Raises temperature, drives winds, ocean currents

Energy input & output averaged over year:

Excess heat in equatorial areas, heat deficit in polar areas

Average surface temperatures:

Higher in equatorial than polar areas

Response to seasonal forcing: temperature changes

Northernhemisphere

Response to seasonal forcing:average surface temperature changes over year

Response to seasonal forcing: albedo changes(temperature-albedo feedback)

Why does land temperature undergo bigger temperature changes, and change more rapidly, than ocean temperature?

Because of differences in “heat capacity”.

Ocean Land

Northern hemisphere

Heat capacity

-- quantity that measures the ability of asubstance to absorb heat

heat capacity = density x specific heat cal / cm3 g / cm3 cal / g

Heat capacity

• water has higher heat capacity than rock• water has a greater ability to store heat

(it is a good “heat sink”)• it takes more energy to raise temperature of water

than rock

Heat capacity

Heat capacity = Density x Specific Heat (cal/cm3) (g/cm3) (cal/g)

For water: 1 g/cm3 1 cal/g

Ratios of heat capacities:

water : ice : air : land = 60 : 5 : 2 :1

so water has a capacity to absorb heat that is 60 times that of the land’s capacity fo absorb heat

On average, surface heats up moreat equator than at poles

• drives winds in atmosphere

• drives ocean currents

• strongly affects climate (& weather)

Heat transfer

• heat flows from hot to cold

• heat transfer by various means-- conduction-- convection-- radiation

• should get flow of heat from equator to poles

• heat imbalances drive winds, precipitationpatterns & ocean currents

Why?

We get flow of air & heat from ground upwards.

“Warm air rises, cold sinks”.

Circulation of atmosphere (winds)

Because:

• most heating at surface

• warm air has lower pressure & density than cold air

• lower density air moves up, higher density air moves down

“Warm air rises, cold sinks”.

Wind

Uneven heating of atmosphere causes it tomove vertically & horizontally acrossthe ground.

Air that moves across surface is called“wind”.

We get systematic wind patterns on planets.

Venus:(1) rotation rate very slow (243 Earth days)(2) get simple wind circulation pattern (northern and southern Hadley Cells)

Hadley Cells

Earth:(1) rotation rate fast(2) get complex wind circulation pattern owing to Hadley Cells + Coriolis Effect

Coriolis Effect

• apparent deflection of moving objects (e.g. airmasses, ocean currents) on planet caused by planetary rotation

• deflection to right in northern hemisphere,to left in southern hemisphere

In red:

apparentpath of objectsmoving towards or away from equator

westerlies

easterlies

Why?

Flow of heat in atmosphere also determinesprecipitation patterns.

“It rains most at the equator, and least in the tropics (+- 30o latitude) and poles”.

Because:

• Warm air can hold more water vapor than cold air

• When warm air rises, it cools

• Equator has lots of warm, wet, rising air

• Subtropics & poles have dry, sinking air

“It rains most at the equator, and least in the subtropics (+- 30o latitude) and poles”.

desert belt rain belt

desert belt

Circulation of oceans (currents)