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 energy across 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 23.5 o

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 Northern hemisphere

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 a substance to absorb heat heat capacity = density x specific heat cal / cm 3 g / cm 3 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/cm 3 ) (g/cm 3 ) (cal/g) For water: 1 g/cm 3 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 more at 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, precipitation patterns & 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 to move vertically & horizontally across the 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. air masses, ocean currents) on planet caused by planetary rotation deflection to right in northern hemisphere, to left in southern hemisphere

In red: apparent path of objects moving towards or away from equator

westerlies easterlies

Why? Flow of heat in atmosphere also determines precipitation patterns. “It rains most at the equator, and least in the tropics (+- 30 o 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 (+- 30 o latitude) and poles”.

desert belt rain belt desert belt

Circulation of oceans (currents)