Earth’s Energy and Seasons

Geronimo R. Rosario

Energy is the ability or capacity to do work on some form of matter.

  Work is the measure of a quantity that is capable of

accomplishing macroscopic motion of a system due to the action of a Force over a Distance. ◦ Force is the agent of change, and Work is a measure of the change.

  Matter is anything that has mass and occupies space.   Three most important ideas of the model:

◦ All substances are made of particles too small to see◦ The particles are always in motion◦ The particles have space between them

Energy

Potential Energy- is the stored energy of position possessed by an object.

 ◦ Gravitational Potential energy- is the energy stored in an object

as the result of its vertical position or height. The energy is stored as the result of the gravitational attraction of the Earth for the object. 

◦ The gravitational potential energy (PEg) of any object is given as;   PEg = mgh,  

◦ Where m is the object’s mass, g is the acceleration of gravity, and h is the object’s height above the ground.

 

Types of Energy

Elastic potential energy- is the energy stored in elastic materials as the result of their stretching or compressing. Elastic potential energy can be stored in rubber bands, bungee chords, trampolines, springs, an arrow drawn into a bow, etc.

  The elastic potential energy (PEe) of any object is given as;   PEe = 0.5 kx2

  Where k is the constant of proportionality of the object and x is

the amount of compression of the object.

Types of Energy

Kinetic energy – is the form of energy that results from object’s motion.

  The kinetic energy (KE) of an object is equal to half its

mass multiplied by its velocity squared; thus;   KE = 1⁄2 mv2   The atoms and molecules that comprise all matter have

kinetic energy due to their motion. This form of kinetic energy is often referred to as heat energy.

Types of Energy

Things to note:   Energy is not a

substance. It cannot be

weighed It does not take

up space Energy

describes a condition

Types of Energy

Law of Conservation of Energy: Energy cannot be created or destroyed. It can only be transformed from one type to another or passed from one object to another. (First law of thermodynamics)

Temperature- is a measure of the average speed of the atoms and molecules, where higher temperatures correspond to faster average speeds.

Thermal Energy - The total energy of all the particles in a material.

The total potential and kinetic energy in an object. It depends on mass, temperature, and phase of an object.

Thermal energy is synonymous to Internal energy The atmosphere and oceans contain internal energy.

Temperature

All of the particles that make up matter are constantly in motion

Solid= vibrating atoms Liquid= flowing atoms Gas= move freely Plasma= move incredibly fast and freely   A plasma is a gas that has been energized to the

point that some of the electrons break free from, but travel with, their nucleus. Ex. Lightning, electric spark, neon lights

Kinetic theory of matter

Thermometer: Mechanical or electrical device for measuring temperature. Early thermometer was invented by Galileo.

Scale: A series of equally measured sections that are marked and numbered for use in measurement

Thermometer

Fahrenheit: Water freezes 32oF and boils at 212oFCelsius: Water freezes at 0oC and boils at 100oCScientists use Kelvin to explain the behaviour of gases.“Absolute Zero” is measured in Kelvin – which is the coldest possible temperature 0 Kelvin = -273 ºC

Formula for Conversion:   oC = (5/9) x (oF-32) oF = (9/5) oC +32 K = °C + 273   Thermal expansion/contraction - change in volume of a material due to

temperature change. Occurs because particles of matter collide more or less as temperature

changes.   Contract: Decrease in volume Expand: Increase in volume Temperature changes cause things to expand and contract Heated – usually causes expansion Cooled – usually causes contraction Usually more drastic in gases, then liquids then solids

Temperature Formula

Heat- is energy in transfer other than as work or by transfer of matter. ◦ When there is a suitable physical pathway, heat flows

from a hotter body to a colder one Heat Capacity: Amount of thermal energy that

warms or cools the object by one degree Celsius. Specific Heat: the amount of energy required to

raise the temperature of 1 gram of a substance by 1oC

Calorie is the unit used for the amount of energy

Heat

Latent- hidden

Latent heat- the quantity of heat gained or loss per unit mass as a substance undergoes a change of state at given temperature.

Latent heat of melting- is the energy needed to break the intermolecular bonds that hold water molecules rigidly in place in ice crystals without an increase in temperature.

Latent heat of vaporization- Is the amount of heat that must be added to 1 gram of a substance at its boiling point to break the intermolecular bonds and complete the change of state from liquid to vapor (gas).

Water’s latent properties

Latent heat of evaporation- the heat energy that must be added to one gram of a liquid substance to convert it to a vapor at a given temperature below its boiling point. 585 calories at 20oC at sea surface

Latent heat is the energy absorbed by or released from a substance during a phase change from a gas to a liquid or a solid or vice versa. 

All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor) but changes such as these require the addition or removal of heat. Heat that causes a change of state with no change in temperature is called latent heat.

Sensible heat is the energy required to change the temperature of a substance with no phase change

When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat

Latent Heat and Sensible Heat

Evaporation from lakes, oceans, rivers, etc. occurs for temperatures lower than 100 oC

Evaporation in the aquatic environments

But it requires more energy to do so

Energy moves heat in three ways

Conduction Convection Radiation

Heat Transfer

process of heat transfer in wave form, without the use or necessity of a transmitting medium. Ex: insolation (radiant energy) from the s

Radiation

All things (whose temperature is above absolute zero), no matter how big or small, emit radiation.

Most of the sun’s energy is emitted from its surface, where the temperature is nearly 6000 K (10,500°F, 5815.6 oC). The earth, on the other hand, has an average surface temperature of 288 K (15°C, 59°F). The sun, therefore, radiates a great deal more energy than does the earth.

Radiation of the Sun and Earth

States that the amount of energy emitted by an object is proportional to the object’s temperature.

 ◦ Stefan-Boltzmann Law describes this mathematically as;

  I =T4

  I is the intensity of the radiation in watts/m2, is the Stefan-Boltzmann

constant (5.67 x 10-8 watts/m2/K4) and T is the temperature of the body in K  

◦ Hotter objects emit more energy than cooler ones ◦ Graybodies denote objects which emit some percentage of the

maximum amount of radiation possible at a given temperature Most solids and liquids

◦ True radiation emitted is a percentage relative to a blackbody and reflects the emissivity of the object

Stefan-Boltzmann Law

The earth emits most of its radiation at longer wavelengths between about 5 and 25 μm, while the sun emits the majority of its radiation at wavelengths less than 2 μm. For this reason, the earth’s radiation (terrestrial radiation) is often called longwave radiation, whereas the sun’s energy (solar radiation) is referred to as shortwave radiation

The transfer of heat by the mass movement of a fluid (such as water and air)

The temperature gradients in the laminar boundary layer induce energy transfer upward through convection◦ This occurs any time the surface temperature exceeds

the air temperature◦ Normally, this occurs during the middle of the day◦ At night, the surface typically cools more rapidly than

air and energy is transferred downward

Convection

Convection can be generated by two processes in fluids◦ Free Convection

Mixing related to buoyancy Warmer, less dense fluids rise

◦ Forced Convection Initiated by eddies and other disruptions to smooth, uniform flow

Free Convection

Forced Convection

The transfer of heat from molecule to molecule within a substance

As the surface warms, a temperature gradient (rate of change of temperature over distance) develops in the upper few cm of the ground

Temperatures are greater at the surface than below◦ This transfers energy downward◦ Surface warming also causes a temperature gradient

within a very thin sliver of adjacent air called the laminar boundary layer

◦ Air is an extremely poor conductor of heat

Conduction

◦ Nearly two (2) calories on each square centimeter each minute or 1367 W/m2

◦ Insolation annually varies by 7%◦ Useful to think of a constant supply of radiation at the

top of the atmosphere◦ Need to account for the relative amount of radiation

that is transmitted through the atmosphere, absorbed by the atmosphere and surface, and scattered back to space

Incoming Solar Energy

Scattering- is the process by which "small particles suspended in a medium of a different index of refraction diffuse a portion of the incident radiation in all directions." ◦ With scattering, there is no energy transformation, but a

change in the spatial distribution of the energy Three different types of scattering

◦ Rayleigh scattering◦ Mie scattering◦ Non-selective scattering

Scattered and Reflected Light

Rayleigh scattering mainly consists of scattering from atmospheric gases. ◦ Involves gases, or other scattering agents that are

smaller than the energy wavelengths◦ Scatter energy forward and backward◦ Partial to shorter wavelength energy, such as those

which inhabit the shorter portion of the visible spectrum

◦ A blue sky results

Scattering

Mie scattering is caused by pollen, dust, smoke, water droplets, and other particles in the lower portion of the atmosphere.

Scattering

o Larger scattering agents, such as suspended aerosols, scatter energy only in a forward manner

o Larger particles interact with wavelengths across the visible spectrum

o Produces hazy or grayish skieso Responsible for the white

appearance of the cloudso Enhances longer wavelengths

during sunrises and sunsets, indicative of a rather aerosol laden atmosphere Longer radiation path lengths lead to

an increase in Mie Scattering and reddish skies

Non-selective scattering- It occurs in the lower portion of the atmosphere when the particles are much larger than the incident radiation. This type of scattering is not wavelength dependent and is the primary cause of haze.◦ Water droplets, typically larger than energy

wavelengths, equally scatter wavelengths along the visible portion of the spectrum

◦ Produces a white or gray appearance◦ No wavelength is especially affected

Scattering

is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated.◦ Process does not increase heat

in the reflector as energy is not absorbed

◦ In most instances, only a portion of incident energy is reflected

◦ Albedo = the percentage of reflected energy

◦ Specular reflection is reflection of energy as an equally intense energy beam

Reflection

Albedo- is the percent of radiation returning from a given surface compared to the amount of radiation initially striking that surface. Albedo, then, represents the reflectivity of the surface

Solar radiation is the primary heat source for the atmosphereMost gases are transparent to solar radiation and, instead,

absorb terrestrial radiationGases are also responsible for scattering incident energySolar input must balance solar outputTemperature increases/decreases if input is greater/less than

outputAverage Earth Temperature is 16oCWithout greenhouse gases, average T is -18oCSolar Energy is reradiated from the surface as a long wave.Surface of Earth (including oceans) is heated from aboveAtmosphere is heated from belowThe balance between incoming solar radiation, the absorption of

terrestrial radiation, and outgoing terrestrial radiation describes the global energy budget

Solar Radiation

Atmospheric Influences on InsolationRadiant energy incident upon the Earth-atmosphere system is

either absorbed, reflected, or transmitted by atmospheric gases and/or the Earth’s surface

Energy reflected and/or transmitted (scattered) does not contribute to heating

Absorbed energy encourages direct heating Absorption

Particular gases, liquids, and solids in the atmosphere absorb radiant energy

Heat increases in the absorber while less energy is transferred to the surface

Although atmospheric gases are rather selective in the wavelengths they absorb, they are overall poor absorbers of energy

Solar Radiation

Blackbody- any object that is a perfect absorber (that is, absorbs all the radiation that strikes it) and a perfect emitter (emits the maximum radiation possible at its given temperature).

Blackbodies do not have to be colored black; they simply must absorb and emit all possible radiation.

Earth’s surface and Sun are blackbodies Selective absorbers- Objects that selectively absorb

and emit radiation, such as gases in our atmosphere.

Absorption

States that good absorbers are good emitters at a particular wavelength, and poor absorbers are poor emitters at the same wavelength.

Atmospheric Window- range of wavelengths not absorbed

Kirchhoff’s law

is the overall dynamic property of the earth's atmosphere, taken as a whole at each place and occasion of interest, that lets some infrared radiation from the cloud tops and land-sea surface pass directly to space without intermediate absorption and re-emission, and thus without heating the atmosphere.

Atmospheric Window

As the main part of the 'window' spectrum, a clear electromagnetic spectral transmission 'window' can be seen between 8 and 14 µm. A fragmented part of the 'window' spectrum (one might say a louvred part of the 'window') can also be seen in the visible to mid-wavelength infrared between 0.2 and 5.5 µm.

There are 2 so-called atmospheric windows  Solar window: lets in almost all visible light and shortwave

infrared light from the Sun Thermal window (confusingly also called the atmospheric

window): allows out some of the longwave infrared from the Earth These energy flows balance to maintain the Earth's temperature.

Atmospheric Window

Global heat budget is the balance between incoming and outgoing solar radiation. Incoming solar energy varies at different times of year and for different locations across the globe.

Heat budget

An estimate of the heat budget for Earth. On an average day, about half of the solar energy arriving at the upper atmosphere is absorbed at Earth’s surface. Light (short-wave) energy absorbed at the surface is converted into heat. Heat leaves Earth as infrared (long-wave) radiation. Since input equals output over long periods of time, the heat budget is balanced.

Earth as a whole is in thermal equilibrium, but different latitudes are not.The average annual incoming solar radiation (red line) absorbed by Earth and the average annual infrared radiation (blue line) emitted by Earth. Polar latitudes lose more heat to space than they gain, and tropical latitudes gain more heat than they lose. The amount of radiation received equal the amount lost at about 38°N and S. The area of heat gained (orange area) equals the area of heat lost (blue areas) so Earth’s total heat budget is balanced.

Heat Budget

Energy imbalance – more energy comes in at the equator than at the poles

51% of the short-wave radiation (light) striking land is converted to longer-wave radiation (heat) and transferred into the atmosphere by conduction, radiation and evaporation.

Eventually, atmosphere, land and ocean radiate heat back to space as long-wave radiation (heat)

Input and outflow of heat comprise the earth’s heat budget

Heat budget

Qs= Qr + Qe + Qh Where: Qs = solar radiation (100%) Qr = radiation (41%) Qe = evaporation (53%) Qh = conduction (6%) Example: If we have 2500 units of Qs, compute for the

Qr, Qe and Qh. Qs= 1025 + 1325 + 150

Heat Budget

How solar energy input varies with latitude.

Equal amounts of sunlight are spread over a greater surface area near the poles than in the tropics.

Ice near the poles reflects much of the energy that reaches the surface there.

The atmosphere reflects, scatters and absorbs solar radiation. At high latitudes solar radiation travels a longer path through atmosphere.

Heat budget by latitudes

Uneven Solar Energy Inputs: Earth is heated unevenly by the sun due to different angles of incidence between the horizon and Sun.

This angle of incidence is affected two factors:

1) Latitude: solar inputs are most dense when the sun is overhead in the tropics; reflection is low. The reverse holds true in polar regions.

2) Season: Due to Earth’s annual orbit around the Sun on an axis tilted by 23.5º.

Latitude (o) Heat received (g cal/cm2/min)   0 0.339 10 0.334 20 0.320 30 0.297 40 0.267 50 0.232 60 0.193 70 0.160 80 0.144 90 0.140

Heat Budget by Latitudes

Heat budget for particular latitudes is NOT balanced

Sunlight reaching polar latitudes is spread over a greater area (less radiation per unit area)

At poles, light goes through more atmosphere so approaches surface at a low angle favoring reflection

Tropical latitudes get greater radiation per unit area and light passes through less atmosphere so they get more solar energy than polar areas

Heat budget by latitudes

Atmosphere and ocean one interconnected system

Change in atmosphere affects ocean Change in ocean affects atmosphere

Ocean and Atmosphere

Equatorial areas excess heat Polar regions heat deficient

Warm equatorial water flows to higher latitudes

Cool Polar water flow to lower latitudes

Re-distribution of heat• Heat gained at Equatorial latitudes• Heat lost at higher latitudes• Winds and ocean currents redistribute heat around the

EarthOceans do not boil away near the equator or freeze solid near the poles because heat is transferred by winds and ocean currents from equatorial to polar regions.

• To compensate for this energy imbalance, winds in the atmosphere and currents in the oceans transport cold air and water toward the equator

• About 1/3 of this transport occurs from the evaporation of tropical waters and subsequent transport into high latitudes, where it condenses and releases latent heat

• About 1/3 occurs from the poleward transport of warm waters by ocean currents

• The remaining 1/3 occurs from middle latitude cyclones and anticyclones

►Due to Energy transfer we get form solar energy and other forms we get different weathers.

►The Effects of the energy transfers in the future could result in melting Ice caps, higher sea levels , flooding, and warmer climate .

► The Polar Ice Caps absorb a lot of the CO2 and solar radiation.

►If these melt then there will be nothing to reflect the harmful radiation and to absorb CO2 .

Effects of Energy Transfer

◦ Earth revolves about the Sun along an ecliptic plane ◦ Distance varies

Perihelion (Jan 3; 148 mil km, 91 mil mi) Aphelion (July 4; 152 mil km, 94 mil mi)

◦ Total variation is about 3%◦ Using the inverse square law, radiation intensity varies

by about 7% between perihelion and aphelion

Earth’s Seasons

Aphelion- the point in the orbit of an object in the solar system that is farthest away from the sun. ◦ 152,200,000 km distance◦ July 4◦ 1.88 cal

Perihelion- point nearest the sun in the orbit of a planet◦ 148,500,000 km distance◦ January 3◦ 2.01 cal

Aphelion and Perihelion

◦ Earth rotates on its axis once every 24 hours

◦ Axis of rotation is offset 23.5o from a perpendicular plane through the ecliptic plane

◦ Because the axis of rotation is never changing, the northern axis aligns with the star Polaris

◦ Hemispheric orientation changes as the Earth orbits the Sun

◦ A particular hemisphere will either align toward or away from the Sun, or occupy a position between the extremes

Earth’s Rotation

Equinox- either of the two annual crossings of the equator by the Sun, once in each direction, when the length of day and night are approximately equal everywhere on Earth.

The equinoxes occur around March 21 and September 23

  Vernal equinox- March 21

(the sun shines directly above the equator)

Autumnal equinox – September 21 (the sun shines directly above the equator)

Equinoxes and Solstices

Solstice- either of the times when the Sun is farthest from the equator, on or about June 21 or December 21

  Summer solstice- June 21

(the sun shines down directly over the tropic of Cancer 23o 27’N )

Winter solstice- December 21 (the sun shines down directly over the tropic of Capricorn 23o 27’S )

Equinoxes and Solstices

Seasons do NOT arise from the distance the Earth is from the Sun but rather as a result of the Earth’s annual motion and axial inclination – the tip of our planet with respect to its orbital plane. As we move around the Sun, the orientation of our planet gives us seasons.