Chapter 4 : Atmospheric Energy and Global Temperatures

Earth's Energy Balance

-Absorbs longwave radiation from the sun (UV, visible, and near infrared)

-Emits shortwave (from reflection) and longwave radiation into space.

-Whatever is absorbed is converted to heat.

Insolation

Incoming solar radiation; Earth's energy input.

What causes greater insolation at low-latitude deserts?

Frequent cloudless skies; less reflection.

Insolation patterns across latitudes

Insolation increases towards lower latitudes (tropics) and decreases at higher latitudes (poles).

Insolation as it approaches Earth

- About half of total insolation arrives at Earth's surface.

-Rest of it is reflected, scattered back into space or absorbed by the atmosphere.

Transmission

-Uninterrupted passage of shortwave and longwave energy through atmosphere or water.

-This is how direct radiation arrives.

Scattering

-Increasing density in atmospheric molecules as insolation approaches Earth's surface. (Remember; less dense higher in atmosphere, more dense as approach surface)

-Atmospheric gases, dust, cloud droplets, water vapor, pollutants, etc. redirect radiation (reflection)

-Does not alter wavelengths.

Diffuse Radiation

- Energy that reaches Earth's surface after scattering.

-Weaker, dispersed, travels in lots of directions.

-Casts shadowless light on ground.

Direct Radiation

- Energy that reaches Earth's surface without being scattered.

Principle of Rayleigh Scattering

- Shorter wavelengths are scattered more.

- Longer wavelengths are scattered less.

Why is the sky blue?

- Rayleigh principle

-Blues and violets are shorter wavelengths so they scatter more, when we look at the sky we are seeing the most scattered wavelengths.

Why are sunsets and sunrises red?

-When the sun is at a lower altitude (horizon), shorter wavelengths are scattered out which leave the orange and reds for us to see.

Refraction

- Changes insolation speed and direction.

-Can be caused by change in medium (going from less dense area to dense area or change in surrounding like going from air to water)

-Example: the rainbow you see when light passes through prism or the distortion of sun at sunset.

Reflection

- When solar energy bounces directly back into space.

- Clouds reflect about 20% of insolation over year.

- Air pollutants also reflect incoming energy.

Albedo

- Reflective quality/intrinsic brightness of a surface.

- Reported as percentage of insolation that is reflected (0% means total absorption, 100% means total reflectance)

Surface colors and albedo

- Dark colored surfaces have lower albedos (more absorption)

- Lighter colored surfaces have more albedo (more reflectance)

Angles and albedo

- lower angles have more reflectance than higher angles

Surface texture and albedo

- Smooth surface has higher albedo than rough surface.

Absorption

- Assimilation and conversion of radiation from one form to another.

-Whatever isn't reflected is absorbed by Earth's surface.

What happens to absorbing surface during absorption?

-It's temperature increases which can change the rate and wavelength of the radiation it emits.

Absorbtion at Earth's Surface vs. Atmosphere

- More absorption occurs at Earth's surface because atmosphere gases are selective about what wavelengths they absorb.

Absorbed solar energy...

- Produces heat

- Reminder: Heat is the flow of kinetic energy between molecules from one body or substance to another because of temperature difference. (Like when you hold a warm mug and the heat flows from mug to your hand- always travels from high to low temp)

What are the two types of heat?

Sensible heat and latent heat

Sensible Heat

- Heat that can be sensed, you feel it.

Latent Heat

- Hidden heat

- Energy gained or loss when a substance changes from one state to another.

- Think of when water changes forms (ice, liquid, gas).

Difference between latent heat and sensible heat

- Latent heat does not cause substance to change temperature when changing physical state.

Specific Heat

Heat capacity of a substance.

Name 4 methods of heat transfer

- Radiation

- Conduction

-Convection

-Advection

Radiation

- Transfer of heat in electromagnetic waves.

-Ex: heat transfer from Sun to Earth

Conduction

- Molecule to molecule transfer of heat energy as it diffuses through a substance.

-Ex: walking on a hot sidewalk barefooted.

Convection

- Transfer of heat by mixing or circulation; vertical.

Ex: Boiling Water

Advection

Similar to convection but horizontal motion

Energy Balance

- Atmosphere energy naturally balances itself.

- inputs of shortwaves balanced by outputs of shortwave and longwave.

-When it is not balanced Earth can undergo a period of temporary warming or cooling that affects climate.

Greenhouse Analogy

- Atmosphere absorbs heat energy and delays transfer of heat into space; causing warming atmosphere.

Greenhouse Gases

- Gases that are mostly transparent to passage of shortwave solar radiation but are effective at absorbing longwave infrared radiation.

-Causes heat in lower atmosphere

Name some greenhouse gases

-Water Vapor
-Methane
-Carbon Dioxide
-Nitrous Oxide
-Ozone
-CFCs

Greenhouse gases and the Earth over the years

- Increase in greenhouse gases; especially carbon dioxide has caused a warming trend.

Clouds

- Reflects shortwave radiation which is why their presence or absence can make a 75% difference in amount of energy that reaches Earth's surface.

- Absorbs longwave radiation; acts as insolation that warm's Earth's atmosphere.

-Low and thick clouds reflect about 90% insolation (stratus and cumulus).

Cloud Albedo Forcing

Increase in thick clouds increases albedo which results in cooling of Earth's climate.

Cloud Greenhouse Forcing

Clouds that act as insolation trap heat and causes warming.

High Altitude ice crystal clouds

Reflect about 50 of incoming insolation but can also trap longwave radiation which raises the temperature (Cirrus)

Aerosols

Can cool or heat Earth's atmosphere (some absorb, some reflect)

Ex: aerosols from volcanic eruptions can block light and have a cooling affect whereas darker aerosols like black carbon absorb radiation and cause a warming effect.

Summary of Inputs and Outputs

- Starting with 100% of solar energy arriving at top of the atmosphere.

- 31% reflected back into space from Earth's average albedo.

-24% absorbed by atmosphere

- 45% transmits through Earth's surface as direct and diffused shortwave radiation.

- Eventually the 69% from absorbed/direct/diffused is emitted back into space.

Summary of Latitudinal Imbalances

- More emitted longwave radiation from subtropical deserts because less clouds and less at polar and tropical lands because more clouds.

- Think of clouds as a lid that can cover longwave radiation going to space.

Reminder from Ch2: in general, polar regions receive less insolation than they emit causing deficits and tropical regions receive more insolation than they emit so surplus.

Daily radiation patterns relate to...

air temperature

Incoming energy throughout the day

- Arrives during sunrise, peaks at noon, ends at sunset.

-Peaks between 3-4pm

-Lowest point right at or slightly after sunrise.

Radiation and temperature curves...

vary with season and latitude

Lag between insolation and air temperature curve occurs because...

Warmest part of the day does not occur until AFTER maximum insolation has been absorbed and emitted.

Microclimatology

the science of physical conditions at or near Earth's surface

Microclimate

Local climate conditions over small area (park)

Net Radiation

Sum of all radiation gains and losses.

Varies with daylength, amount of cloud cover, and latitude.

Positive during day, negative during night.

Energy Exchange

Positive when moving from atmosphere to surface (usually day) and negative when moving from surface to atmosphere (usually night)

..Think about how it gets colder at night- energy being loss.

Name 3 processes for Net Radiation Expenditure

- Latent Heat of Evaporation
-Sensible Heat
-Ground Heating and Cooling

Latent Heat and Evaporation

-Energy absorbed by water as it changes from liquid to gas.

-This absorption removes heat energy from surface.

-Dominant mechanism for dissipating net radiation gains.

-Highest at tropics, decreases as you move towards poles.

Sensible Heat

-heat transferred back and forth between air and surface through convection and conduction within materials.

-dissipates 1/5 of Earth's entire NR

-Highest at subtropics

Ground heating and cooling

flow of energy into and out of ground by conduction

Reminder from previous chapter; Temperature vs. Heat

Heat is a form of energy and temperature is what measures that energy

Absolute Zero

Lowest possible temperature at which atomic and molecular motion in matter completely stops.

Fahrenheit

-Daniel G. Fahrenheit
-Melting Point of Ice: 32F
-Boiling Point of Water: 212F

Celsius

-Anders Celsius
-Melting point of Ice: 0C
-Boiling Point of Water : 100C

Kelvin

-Lord Kelvin
-Melting Point of Ice: 273K
Boiling Point of Water: 373K

Why are mercury thermometers ineffective for assessing Earth's colder climates?

Mercury freezes at 38.2F

Land Surface Temperature

-Heating of land surface
-How satellites measure air temperature
-Highest in dry environments with clear skies and low albedo.

Principle Temperature Controls

latitude, altitude/elevation, cloud cover, land-water heating differences

Latitude

-Insolation more intense between tropics because sun is more direct.
-Insolation decreases as you move towards poles.
-Daylength varies with latitude which also affects insolation.

Altitude/Elevation

-Altitude: airborne objects of heights above Earth's Surface.

-Elevation: height of point on Earth's surface.

-Temperature decreases with altitude because molecule density decreases with altitude.

-Less molecules = less collisions = less heat = lower temp.

-Mountains have lower temperature than sea level;they lose energy quicker

Cloud Cover

-Any moment 50% of Earth covered by clouds
- Less clouds = cooler because clouds act as insulation.

Land-Water Heating Differences

-Land and water absorb and store energy differently.
-Land heats and cools faster than water.

Reasons for Land-Water Heating Differences

Evaporation, transparency, specific heat, movement, ocean currents and sea surface temperatures.

Evaporation

- Evaporation dissipates more energy over water than land; so lots of it over oceans.

-Evaporation absorbs heat energy and stores as latent heat which causes its surroundings to cool.

Transparency

-Waters transparency allows larger area of heat distribution so more heat is stored than land as a result.

Specific Heat

Energy required to increase temperature of water is greater than land

Movement

Water is fluid and capable of movement which allows mixing of cooler and warmer waters.

Ocean currents and sea surface temperatures

-Cool ocean currents flow from high latitudes to low, carrying colder water down.

-Similarly, warm currents can have warming effects.

Marine Effect

Oceans moderate temperature changes from day to night and during different seasons

Occurs along coastlines or islands

Dominate in Southern hemisphere

Continental Effect

land areas have greater range of temperatures from day to night and during different seasons

Occurs inland/ areas distant from large bodies of water.

DOminate in northern hemisphere

Isotherm

An isoline that connects patterns of equal temperature

January

High sun altitudes and longer days in southern hemisphere; summer

Low sun altitudes and shorter days in northern hemisphere; winter

Isotherms show decrease in insolation and net radiation with distance from the equator.

Thermal equator moves southward towards South America and Africa.

July

High sun altitudes and longer days in northern hemisphere; summer

Lower sun altitudes and shorter days in southern hemisphere; winter

Thermal equator moves northward

Thermal Equator

Line around earth connecting all points of highest mean temperature

Annual Temperature Range

Difference between the highest and lowest average annual temperatures for that location.

Largest average annual temperature ranges occur in subpolar locations.

More seasonal temperature variation in north, more land less water than southern hemisphere.

Polar Region Temperatures are...

more moderate than south

Cold Snap

a short period of cold weather

Heat Wave

a prolonged period of abnormally hot weather

Global Temperature Anomaly

An irregularity in temperature. (Like an outliar)

Positive anomalies indicate warmer temperatures than average.

Negative anomalies indicate cooler temperatures than average.

Arctic Amplification

Tendency for polar latitudes to experience enhanced warming relative to the rest of the planet.

Urban Heat Island

Maximum and minimum temperatures higher than nearby rural areas.

Highest in cities with dense population.

Lower in cities with more urban sprawl.

Some Causes:
Asphalt and glass
Building geometry
Pollution
Industry and transportation

Dust Dome

Trapped airborne pollution.

Pollutants collect due to decrease in wind speed then rise as surface heats and remains in air above city.

How some cities mitigate effects of UHI

Include vegetation

Include parks and open space

High albedo roofs

Average internal body temperature

36.8C

Humidity

The amount of water vapor in the air

Wind speed and air temperature affect our sense of comfort

Wind Chill

Correlates cold and wind speed.

Stronger wind, lower wind chill index.

Lower wind, higher wind chill index.

Heat Index

Correlates heat and humidity

Higher humidity, higher heat index

Lower humidity, lower heat index.