WEAX 201 Lesson 3 - Atmospheric Energetics

what are the 3 heat transfer mechanisms?

• rad…

• con…

• conv…

• radiation

• conduction

• convection

what is radiation? examples?

• transfer of energy by…

• can occur across…

• examples:

• transfer of energy by electromagnetic waves (light)

• can occur across empty space

• examples: microwaves, cell phone signals, visible light, xrays, etc

• campfire: you feel the warmth on your face and hands when sitting next to a fire, even though the hot air or flames are not touching you

what is conduction?

• transfer of heat from…

• examples:

• transfer of heat from one molecule to another

• examples: cooking on a stove, melting chocolate, walking on hot sand, ironing clothes

• campfire: a metal roasting stick gets dangerously hot to the touch because heat travels directly through the metal from the fire

what is convection?

• random vertical…

• transport by horizontal…

• examples:

• random vertical air motions

• transport by horizontal air motions = advection

• examples: hot air balloons, room heaters, convection ovens

• campfire: the air directly above the fire gets hot, becomes lighter, and rises into the sky, creating currents of warm air

what is adiabatic cooling/heating?

• when air goes up and down, its temperature can change () being lost or gained

• it requires () to () or () air

• when air rises, it () and () - with enough temperature ()/() form

• when air sinks, it () and () - clouds tend to ()

• when air goes up and down, its temperature can change WITHOUT HEAT being lost or gained

• it requires work energy to expand or compress air

• when air rises, it expands and cools - with enough temperature clouds/precipitation form

• when air sinks, it compresses and warms - clouds tend to dissipate (clearing skies)

what is stefan-boltzman law?
- energy/area is () to () to the () power

• describes the intensity of the () emitted by ()

• energy/area is proportional to temperature to the 4th power

• describes the intensity of the thermal radiation emitted by matter

what is wien’s law?

• peak wavelength is emitted (…) to temp

• sun emits mainly (), earth ()

• incoming () radiation warms ground

• outgoing () radiation cools ground

• peak wavelength is emitted inversely proportional to temp

• sun emits mainly visible light, earth infrared

• incoming solar radiation (insolation) warms ground

• outgoing infrared radiation (terrestrial radiation) cools ground

what happens to insolation?

• () absorbed by earth and its atmosphere

• () reflected back to space

• the earth has an albedo of ()

• 70% absorbed by earth and its atmosphere

• 30% reflected back to space

• the earth has an albedo of 30%

why are there colors in the sky?

• as sunlight penetrates the atmosphere…

• shorter wavelengths scatter…(makes sky appear () )

• when the sun is low on the horizon…

• longer wavelengths are…(long path through air - gives more () in the sky)

• as sunlight penetrates the atmosphere, molecules scatter visible light in all directions

• shorter wavelengths scatter more in air (makes sky appear blue)

• when the sun is low on the horizon, aerosol and clouds scatter light in forward directions

• longer wavelengths are scattered more (long path through air - gives more red appearance in the sky)

why is the troposphere warmest near the surface?

• the surface absorbs () and () the air directly above it

• the surface absorbs solar energy and heats the air directly above it

where is most of the incoming solar radiation absorbed?

• mostly from () and () rather than the atmosphere

• a smaller portion is absorbed by (), (), and () in the atmosphere

• mostly from lands and oceans rather than the atmosphere

• a smaller portion is absorbed by clouds, water vapor, and gases in the atmosphere

how is the solar energy transferred to the air?

• solar radiation () through the atmosphere without () it significantly

• instead, sunlight () the () and () first

• that () moves from the () surface into the () layer of air and then circulates ()

• solar radiation passes through the atmosphere without heating it significantly

• instead, sunlight warms the ground and water first

• that heat moves from the warm surface into the lowest layer of air and then circulates upward

which heat mechanisms are involved?

• radiation: the sun sends () through space () to reach earth

• conduction: the () ground transfers heat through () to the () layer of air molecules sitting right on top of it

• convection: (), less () air near the surface (), while (), () air (), creating () currents that distribute () throughout the troposphere

• latent heat: energy is also transferred when water changes (), such as () and ()

• radiation: the sun sends energy through space via electromagnetic waves to reach earth

• conduction: the warm ground transfers heat through direct contact to the thin layer of air molecules sitting right on top of it

• convection: warm, less dense air near the surface rises, while cooler, denser air sinks, creating vertical currents that distribute heat throughout the troposphere

• latent heat: energy is also transferred when water changes phases, such as evaporation and condensation

what are the 3 factors affecting surface heating?

1. amount of solar radiation absorbed

2. heat capacity = the amount of heat needed to raise temperature a given amount

3. depth to which heat is distributed

explain “amount of solar radiation absorbed”

• solar elevation angle (angle of sun over horizon) which is affected by time of day, latitude, and season

• albedo (fraction of solar radiation reflected) - dark soil (lower albedo) vs clouds or snow (high albedo)

explain “heat capacity = the amount of heat needed to raise temperature a given amount”

• which changes temperature more rapidly? soil or water?

• water has high heat capacity, soil has low heat capacity

• soil because it has a lower heat capacity and needs much less energy than water to change its temperature, also sunlight warms only the top layer of soil which concentrates the heat in a small area, also soil is solid

explain “depth to which heat is distributed”

• Therefore, why are oceans considered heat reservoirs?

• heat is absorbed over a greater depth of water

• water has a high specific heat capacity which allows it to absorb and store massive amounts of solar energy and excess greenhouse gas heat without a drastic change in temp

what is the effect of the solar elevation angle?

• the solar elevation angle determines the () of () and () reaching the earth’s surface, driving (), climate (), and solar energy ()

• higher solar angles (closer to 90 degrees) concentrate () over a () surface area, leading to () heating. low angles spread light across a () area and requires () to pass through more atmosphere, () intensity

• the solar elevation angle determines the intensity of solar radiation and heat reaching the earth’s surface, driving temperature changes, climate patterns, and solar energy production

• higher solar angles (closer to 90 degrees) concentrate solar energy over a smaller surface area, leading to intense heating. low angles spread light across a wider area and requires rays to pass through more atmosphere, reducing intensity

Why do subtropical oceans absorb the most solar radiation?

• low solar…

• low cloud…

• low () of water

• combine () solar angles with () cloud cover in persistent () descending air zones

• high solar angles

• low cloud cover

• low albedo of water

combine high solar angles with minimal cloud cover in persistent dry descending air zones

why do we have seasons?

• earth’s axis is tilted at an angle of about 23.5 degrees as it travels around the sun relative to its orbital plane

what is the vernal equinox?

• march () in () hemisphere

• Day = () hr (except at (), getting longer)

• march 20-21 in N hemisphere

• Day = 12 hr (except at poles, getting longer)

what is the summer solstice?

• june () in () hemisphere

• sun’s rays directly over () degrees ()

• north of (), the sun never goes ()

• june 21-22 in N hemisphere

• sun’s rays directly over 23.5 degrees N

• north of arctic circle, the sun never goes down

what is the autumnal equinox?

• sept () in () hemisphere

• day = ()hr (except poles, getting ())

• sept 22-23 in N hemisphere

• day = 12hr (except poles, getting shorter)

what is the winter solstice?

• dec () in () hemisphere

• sun’s rays directly over () degrees ()

• north of (), the sun never ()

• dec 21-22 in N hemisphere

• sun’s rays directly over 23.5 degrees S (-23.5)

• north of arctic circle, the sun never rises

At which latitude are the sun’s rays most direct throughout the year?

• the equator (0 degrees latitude)

what is the noontime solar elevation angle equation?

What influences how much infrared radiation Earth emits?

• Surface (): Because of the fourth-power relationship in the Stefan-Boltzmann law, even () in Earth's surface temperature lead to a () increase in the infrared energy it radiates.

• () Gas Concentration: Greenhouse gases (like water vapor, carbon dioxide, and methane) absorb () and () it in all directions. Higher concentrations of these gases () more heat, () the amount of infrared radiation that immediately escapes directly into space.

• () Cover: Clouds act as a (). () clouds tend to () infrared radiation rising from the surface, while (), () clouds () infrared radiation into space from their () (which are cooler than the Earth's surface).

• Surface () (Reflectivity): While albedo directly controls how much () radiation is absorbed, it indirectly drives (). Surfaces with low albedo (like dark oceans) () more sunlight, () up, and consequently () more infrared radiation.

• Surface Temperature: Because of the fourth-power relationship in the Stefan-Boltzmann law, even small increases in Earth's surface temperature lead to a massive increase in the infrared energy it radiates.

• Greenhouse Gas Concentration: Greenhouse gases (like water vapor, carbon dioxide, and methane) absorb outgoing infrared radiation and re-emit it in all directions. Higher concentrations of these gases trap more heat, reducing the amount of infrared radiation that immediately escapes directly into space.

• Cloud Cover: Clouds act as a blanket. High, thin clouds tend to trap infrared radiation rising from the surface, while low, thick clouds emit infrared radiation into space from their tops (which are cooler than the Earth's surface).

• Surface Albedo (Reflectivity): While albedo directly controls how much solar radiation is absorbed, it indirectly drives infrared emission. Surfaces with low albedo (like dark oceans) absorb more sunlight, warm up, and consequently emit more infrared radiation.

When does the earth emit more radiation?

• when its surface is (), it gives off more ()

• when its surface is warmer, it gives off more radiation

What happens to its temperature as it radiates?

• the earth’s temperature () as it emits radiation because radiating energy causes a () of () energy

• air () and () IR radiation - greenhouse gases keep earth () by reducing () lost to space

• the earth’s temperature decreases as it emits radiation because radiating energy causes a net loss of thermal energy

• air absorbs and re-emits IR radiation - greenhouse gases keep earth warmer by reducing infrared radiation lost to space

On the whole, the earth emits the () amount of energy it () from the sun.

On the whole, the earth emits the same amount of energy it receives from the sun.

why is that not the case for individual regions? for example, the tropics or regions poleward of around 37 degrees latitude?

• tropics: () solar radiation is () than () radiation

• regions poleward: experience a radiation () ( () radiation is () than () solar radiation

• tropics: incoming solar radiation is greater than outgoing radiation

• regions poleward: experience a radiation deficit (outgoing radiation is greater than incoming solar radiation

What prevents the tropics from warming and the high latitudes from cooling to reach a balance?

• atmospheric (): approx 60-70% of heat transport, () air () at the equator and moves toward the (), while () air () at the poles and moves toward the ()

• ocean (): approx 30-40% of heat transport as surface ocean currents, driven by (), push () tropical waters toward the () while (), () water () and floats back toward the ()

• atmospheric circulation: approx 60-70% of heat transport, warm air rises at the equator and moves toward the poles, while cold air sinks at the poles and moves toward the equator

• ocean currents: approx 30-40% of heat transport as surface ocean currents, driven by winds, push warm tropical waters toward the poles while cold, dense water sinks and floats back toward the equator

by what means?

• () sensible heat ( () atmos, () oceans )

• () latent heat

• 70% sensible heat (30% atmos, 40% oceans)

• 30% latent heat

what is diurnal radiation balance?

• the daily cycle of () and () energy at the earth’s surface over a () hr period

• the daily cycle of incoming and outgoing energy at the earth’s surface over a 24 hr period

() energy > () means T ()

Incoming energy > outgoing means T rises

() energy < () means T ()

incoming energy < outgoing means T falls

when do maximum and minimum temperatures occur?

incoming energy () outgoing

incoming energy = outgoing

the air is heated and cooled from below WHEN:

1. If (), () night, get () dense layer of air near surface

(a.k.a. ())

2. () mixes () surface air with () air above, ()

cooling near ground

3. ()/() absorb () radiation and () it back

- reduces cooling

1. If calm, cloudless night, get cold dense layer of air near surface

(a.k.a. inversion)

2. Wind mixes cold surface air with warmer air above, reducing

cooling near ground

3. Cloud/moisture absorb outgoing radiation and re-radiate it back

- reduces cooling

Therefore, where and under what conditions is the diurnal (day-to-day) temperature range greatest?

• high-elevation ()

• (…) areas far from moderating influence of ()/large bodies of ()

• next to the ()

key conditions:

• low () and () air

• (), () skies

• sparse () and () soil

• high-elevation deserts

• dry inland areas far from moderating influence of oceans/large bodies of water

• next to the ground

key conditions:

• low humidity and dry air

• clear, cloudless skies

• sparse vegetation and dry soil

when do we get low temperatures?

• near sunrise

when do we get high temperatures?

• late afternoon

when are these not true?

• () and (): heavy rain, thunderstorms, or sudden heavy snow can () the air rapidly during the middle of the day

• changing…: gusty winds can bring in a completely different () of () or () air at any hour, overriding the sun

• cloud ()/(): thick () or () can act like a (), () heat overnight to prevent normal cooling or block the sun during the day

• passing (): a () front or () front moving through during the day or night can cause temps to () or ()

• storms and rain: heavy rain, thunderstorms, or sudden heavy snow can cool the air rapidly during the middle of the day

• changing wind direction: gusty winds can bring in a completely different mass of warm or cool air at any hour, overriding the sun

• cloud cover/fog: thick clouds or fog can act like a blanket, trapping heat overnight to prevent normal cooling or block the sun during the day

• passing fronts: a cold front or warm front moving through during the day or night can cause temps to rise or fall

what is latent heat?

• energy released or absorbed when water changes state without changing its temperature

What happens to incoming solar radiation?

• () and (): () and () surfaces like ice () about 30% of incoming sunlight straight back into space

• atmospheric…: (), (), and () absorb roughly 23% of (…) into the atmosphere

• surface (): nearly half of the solar radiation reaches and () earth’s land and oceans

• reflection and scattering: clouds and bright surfaces like ice reflect about 30% of incoming sunlight straight back into space

• atmospheric absorption: gases, dust, and ozone absorb roughly 23% of solar energy into the atmosphere

• surface absorption: nearly half of the solar radiation reaches and warms earth’s land and oceans

What happens to outgoing infrared radiation?

• thermal (): earth () the () solar energy back () as longwave (….) (heat)

• greenhouse (): greenhouse gases like co² and water vapor () much of this () heat and () in all directions

• space (): some (…) passes directly through the atmosphere’s open windows into space, () the planet

• thermal emission: earth releases the absorbed solar energy back upward as longwave infared radiation (heat)

• greenhouse trapping: greenhouse gases like co² and water vapor absorb much of this outgoing heat and re-emit in all directions

• space escape: some infrared radiation passes directly through the atmosphere’s open windows into space, cooling the planet

What controls the temperature of the atmosphere, the oceans, and the surface of the earth?

• uneven heating of the sun