Chapter 2: Heating and the Earth's Atmosphere

How many million of miles away from earth is the Sun?

The sun is about 93 million miles away from the earth

How big is the sun diiameter?

The sun’s diameter is 109 times that of the earth

What is solar irradiance?

it is the amount of radiant power from the sun received per unit on earth.

Solar Irradiance = insolation = energy per unit time per unit area

[Earth’s Motion ] What is rotation ?

it is the spinning of the earth on its tilted axis (23.5 degree tilt)

[earth motions] what is revolution?

movement of earth around the sun

[earth motions] what is perihelion?

it is the point in orbit closest to the sun

[earth motions] what is a aphelion?

it is the point in orbit farthest from the sun

what is latitude?

latitude are lines, imaginary lines on the earth which run east and west but measure a degree north or south from the equator.

what is longitude?

Longitude lines are imaginary lines on the Earth but these lines run north and south but measure a degree east or west from the prime meridian.

Remember earth rotates 360* / 24 hr = 15* per hour. which defines the Time Zones.

what are the impacts of the important lines of latitude and longitude?

Important lines of latitude are a direct consequence of the Earth’s tilt.

What causes the seasons?

The primary cause of Earth’s seasons is the earth’s tilt. This changes the angle of the sun’s rays at earth’s surface causing different amounts of energy to be absorbed throughout the year.

So what season is in the Southern Hemisphere (enter image later)?

Winter. Because the southern hemisphere is tilted away from the sun. Southern hemisphere spring begins on Sept. 22. (Like how in Australia they celebrate christmas completely different from us)

[earth sun geometry] what is the sun angle?

sun angle is the angle between the surface and the sun’s rays

[earth sun geometry] what is the Zenith Angle?

Zenith Angle is the angle between sun’s rays and the vertical (lines perpendicular to the surface)

How do you find out the solar declination?

TO find the solar declination the formula is = 23.5 x SIN (N).

N is the number of days to the nearest Equinox.

N is (+) between March and September while (-) is between september and march

[earth sun geometry] What is the solstices (June and December 21st or 22nd)?

During the summer Northern Hemisphere titled towards the sun. Solar declination is at 23.5*N.

Winter Southern Hemisphere tilted toward the sun. Solar declination is at 23.5*S.

Basically on the solstices we have max and min daylight.

[earth sun geometry] What is the Equinoxes? (March and September 21st or 22nd)

During the spring (vernal) Earth is not titled away or towards sun. Solar declination is at 0*.

Fall (Automnal) Earth is not tilted away or toward the sun. Solar Declination is 0*

So on the equinoxes we have equal daylight at every location on earth.

How do sun angles vary with latitude?

• In tropics, Sun angle is high and changes somewhere between 23.5* and 47* throughout the year and have 2 days with SA = 90 (1 day at 23.5 Latitude).

• Outside the topics, the sun angle NEVER reaches 90*. All locations between tropics and polar regions have a sun angle which varies by exactly 47* throughout the year. No days with SA= 0 or 90*.

• whereas in the Polar Regions have low sun angles which changes by 23.5* and 47*.

[calculations] What is the solar elevation (sun) angle?

90* [Difference (degree measure “distance”) Between location’s latitude and solar declination) = 90*- ZA

[calculations] What is the Zenith Angle?

Difference (degree measure “distance”) between location’s latitude and solar declination ) = 90 -SEA

[ Calculation ] What is the solar declination aka the Sub solar point?

Latitude at which the sun’s rays are perpendicular to earth’s surface.

What is the impact of Daylight hours over the globe?

• Length of daylight (in addition to solar intensity) is another principal factor that determines solar radiation receipt on earth.

• circle of illumination at any given time half of the earth is illuminated by the sun

• Daylight length changes daily throughout the year for every location not on the equator.

• So solar radiation exposure time, like solar intensity, is not distributed uniformly on earth. Except on the equinoxes (everywhere receives 12 hours of daylight)

So in NYC what direction is the best to face solar panels?

South because we never directly hit the sunlight. (think about the ppl who look for south facing apartments bcs of the sunlight)

Which planet(s) would have the highest seasonality and which ones would have the least?

Uranus experiences the most extreme seasonal variations. While venus experiences the least seasonality effectively having none at all.

What is temperature?

Temperature is the average kinetic energy of the atoms or molecules in a substance

What is heat?

Heat is energy transfered into or out of an object because of temperature differences between that object and its surroundings. Also referred to as thermal energy (total energy contained in a substance due to its temperature)

What is latent heat?

Latent Heat is heat released or absorbed due to phase changes

what is sensible heat?

Sensible heat is heat that we can feel and measure but does not result in a phase change.

(mechanism of heat transfer) What is conduction?

Conduction is the heat transferred through collisions of molecules and electrons from one molecule to another.

(mechanism of heat transfer) What is convection?

Convection is the heat transferred via movement or circulation of a fluid substance due to changes in density.

• Advection primarily describes the horizontal component of convective flow.

(mechanism of heat transfer) What is radiation?

radiation is the movement of thermal energy from one object or system to another due to a temperature difference.

Stefan Boltzman Law (Put in the picture later)

States that the time amount of energy emitted by a body per unit area across all wavelenghts per unit time is proprotional to its temperature.

Wien’s Displacement Law (Put pic in later)

describes the “character” of the radiation. More specifically, it describes an inverse relationship between a body’s temperature and its peak (most common) emission wavelength.

Warmer temps = SHORTER wavelengths of peak emission

What are the laws of radiation?

• all objects continually radiate energy from a range of wavelengths.

• hotter objects radiate more total energy per unit area than colder ones (Stefan Boltzmann Law)

• Hotter objects radiate more shortwave radiation than cooler ones (Wien’s displacement law)

• objects that are good absorbers of radiation are also good emitters.

What happens to incoming solar radiation?

Transmission

absorption

reflection

scattering

What is transmission?

Transmission is the passing of energy through the atmosphere without interacting with gases or other particles.

What is absorption?

Lights gets absorbed and reemitted at another lower wavelength

what is reflection?

Light bounces back from an object at the same angle and intensity

what is scattering?

scattering produces a large number of weaker rays traveling in different directions.

What determines how much energy is absorbed at the surface?

albedo

surface roughness

cloud cover

sun angle

What is albedo?

the percent of light reflected from a surface due to its color, roughness and incident ray angle.

• high albedo means mostly reflection while low albedo means mostly absorption

What is surface roughness?

Smoother surfaces reflect more light → leads to higher albedo.

what is cloud cover?

More cloud cover blocks radiation from both leaving the earth system and entering.

what is sun angle?

Decreased sun angle increases albedo meaning more sunlight is reflected at sharp angles.

Why is the sky blue?

The sky is blue because blue light is scattered most efficiently through our atmosphere.

Then why are sunsets red?

When the sun is setting its light passes through a greater length of the atmosphere allowing all shorter wavelengths to be filtered out and leaving red and orange behind.

Heating of the atmosphere

• gasses in Earth’s atmosphere absorb mostly outgoing longwave radiation from the earth (absorbing then reemitting heat)

• ozone absorbs incoming shortwave UV radiation

• CO2 and H20 absorb outgoing LW radiation

What are greenhouse gases?

Gaseous molecules which absorb outgoing longwave radiation. Most important are CO2 and H20.

What are Greenhouse effect?

Greenhouse gases absorb outgoing LW radiation and re-emit in all directions, including back down to the surface. These gases act as a blanket essentially trapping heat in our atmosphere. (PICK UP FROM SLIDE 60).