Atmosphere-Energy Balance

Latent heat

(Changes in energy state during evaporation/condensation) Energy Balance is the energy released or absorbed when a substance changes from one state to another (evaporation, condensation and freezing of water). When energy is added to water it will change states or phase. The phase change of a liquid to a gas is called evaporation. If we could see down to the molecular level we would find water being comprised of cluster of water molecules (H2O). The clusters are bound together by bonding between the hydrogen atoms of water molecules. The heat added during evaporation breaks the bonds between the clusters creating individual molecules that escape the surface as a gas. The heat used in the phase change from a liquid to a gas is called the latent heat of vaporization. We say it is "latent" because it is being stored in the water molecules to later be released during the condensation process. We can't sense or feel latent heat as it does not raise the temperature of the water molecules. .

diffuse radiation

(D) is shortwave radiation that has been scattered by gases in the atmosphere. Scattering is a process whereby a beam of radiation is broken down into many weaker rays redirected in other directions.

Direct radiation

(S) is shortwave radiation able to penetrate through the atmosphere without having been affected by constituents of the atmosphere in any way.

Net Energy Exchange =

342 - 107 - 235 = 0-keep the ground temperature around the same

Thermals (convective processes)

A thermal column (or thermal) is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and an example of convection. The Sun warms the ground, which in turn warms the air directly above it.

Non-radiative heat transfer

Available net radiation (Q*) is used to do work in the Earth system. The principal use of this energy is in changing the temperature the subsurface (ground heat, G), the air (sensible heat, H), and the phase change of water (latent heat, LE) or, Q* = G + H + LE

Energy Balance

Clouds warm at night and cool during the day

Short Wave Related terms

Direct/diffuse radiation Albedo - values for different surfaces/global average Net shortwave radiation

Seasonal variations in incoming shortwave (solar radiation)

During the vernal equinox the night and day are 50/50 The axis is tilted LOOK UP MORE

Net Radiation Balance

Gathering all the radiation terms together we have net radiation: Q*= [(S+D) - (S+D)a] + [L↓ - L↑] ***Net radiation can be positive, negative, or even zero.*** Net radiation is a positive value when there is more incoming radiation than outgoing radiation. This typically occurs during the day time when the sun is out and the air temperature is the warmest. At night, net radiation is usually a negative value as there is no incoming solar radiation and net longwave is dominated by the outgoing terrestrial longwave flux. Net radiation is zero when the incoming and outgoing components are in perfect balance, which doesn't occur too often.

Longwave radiation related terms

Greenhouse effect/Greenhouse gases Net longwave radiation

Electromagnetic radiation

Hotter the object , greater electromagnetic radiation, shorter waver Electromagnetic radiation travels through space in the form of waves. Unlike heat transfer by convection or conduction, heat transfer by electromagnetic radiation can travel through empty space, requiring no intervening medium to transmit it. The quantity of energy carried in a wave is associated with the height or amplitude of the wave. Everything else being equal, the amount of energy carried in a wave is directly proportional to the amplitude of the wave. The type or "quality" of radiation depends on the wavelength, the distance between successive crests. The greater the distance between wave crests, the longer the wavelength.

Changes in atmospheric density, pressure and temperature with altitude

LOOK UP

Influence of coastal environment on seasonal variations in temperature - importance of differences in specific heat of land and water

Specific heat is the amount of energy needed to raise the temperature of 1 gram of material by 1oC. Specific heat is different for every substance, a function of the molecular structure. Water has an unusually high specific heat.

Non-radiative heat transfer related terms

Subsurface heat (ground) Sensible heat Conduction/Convection - Transfer from surface (land and water) to atmosphere Thermals (convective processes)

Temperature/heat

Temperature is proportional to the average speed (kinetic energy) of the atoms or molecules in an object (matter).

Geographic and seasonal changes in surface temperatures

The different lines in the images are longitudinal Continentality is the tendency of land to experience more thermal variation than water, due to the land's lower specific heat capacity.

Greenhouse effect/Greenhouse gases

The energy absorbed at the surface is radiated by the Earth as terrestrial longwave radiation (L↑). The amount of energy emitted is primarily dependent on the temperature of the surface. The hotter the surface the more radiant energy it will emit. Certain gases of the atmosphere (namely CO2 and water vapor) are relatively good absorbers of longwave radiation and thus absorb the energy emitted by the Earth's surface. The absorbed radiation is emitted downward toward the surface as longwave atmospheric counter-radiation (L↓) keeping near surface temperatures warmer than they would be without this blanket of gases. This is known as the "greenhouse effect".

Maximum wavelength - function of temperature

The maximum wavelength at which a body emits radiation depends on its temperature. Wein's (pronounced "weens") Law states that the peak wavelength of radiation emission is inversely related to the temperature of the emitting body. That is, the hotter the body, the shorter the wavelength of peak emission. The figure below shows the wavelengths over which the sun and earth emit most of their radiation. The Sun being a much hotter body emits most of its radiation in the shortwave end and the Earth in the longwave end of the spectrum.

Radiation balance

The radiation balance of the Earth system is an accounting of the incoming and outgoing components of radiation. These components are balanced (incoming (short wave) = outgoing(long wave)) over long time periods and over the Earth as whole. If they weren't the Earth would be continually cooling or warming. However, over a short period of time, radiant energy is unequally distributed over the Earth, resulting in periods of localized heating and cooling.

Shortwave

The radiation balance of the Earth system is depicted in the above figure. (shortwave radiation is colored yellow and longwave radiation is in red.) Shortwave radiation from the Sun penetrates through space to the outer edge of the atmosphere unimpeded by the vacuum of outer space. ***If one places a surface oriented perpendicular to an incoming beam of light, 1360 W m2 of solar radiation will be received. This value is known as the solar constant** but actually varies by a small amount as the Earth-Sun distance changes through the year. When the solar constant is averaged over the entire Earth surface we get a value of 342 W m2. Once solar radiation begins to penetrate through the atmosphere this amount begins to decrease due to absorption and reflection.

the equation of direct, diffuse radiation

Together, direct and diffuse shortwave radiation accounts for the total incoming solar radiation or insolation (K↓). In equation form: K↓ = S+D

Conduction/Convection

Transfer from surface (land and water) to atmosphere

Geographic (latitude) variations in incoming shortwave (solar radiation)

When the Sun shines directly over the equator, the equator receives the most intense solar radiation, and the poles receive little. Latitude and longitude allow navigators to identify a location on a spherical Earth.

Sensible heat

is heat energy transferred between the surface and air when there is a difference in temperature between them. A change in temperature over distance is called a "temperature gradient". In this case, it is a vertical temperature gradient, i.e., between the surface and the air above.

Net shortwave radiation

is the difference between incoming and outgoing shortwave radiation expressed as: K*= (S+D) - (S+D)a During the day, K* is a positive value as incoming always exceeds outgoing shortwave radiation. At night, K* is equal to zero as the Sun is below the horizon.

Subsurface heat (ground)

major use of radiant energy is to warm the subsurface of the Earth. Heat is transferred from the surface downwards via conduction. A temperature gradient must exist between the surface and the subsurface for heat transfer to occur. Heat is transferred downwards when the surface is warmer than the subsurface (positive ground heat flux). If the subsurface is warmer than the surface then heat is transferred upwards (negative ground heat flux).

Dominant components of the atmosphere

nitrogen and oxygen

Net longwave radiation

the difference between incoming and outgoing longwave radiation is net longwave radiation expressed as: L* = L↓ - L↑

Albedo

values for different surfaces/global average A portion of the incoming solar radiation is absorbed by the surface and a portion is also reflected away. The proportion of light reflected from a surface is the_______ The amount of reflection (K↑) is given by the following equation:K↑ = (S+D)a