Atmosphere and Ocean Heat Budgets

02.12.2012 Atmos. & Ocean Heat Budgets ([email protected])

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Atmosphere & Oceanic Heat

BudgetsDr. Tarek M. El-GeziryLab. of Physical OceanographyDivision of Marine Environment


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Objectives: What is a heat budget? Heat vs Temperature Heat Balance of the Atmosphere Oceanic Heat Budget


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The heat budget of a system consists of inputs and outputs.

"Input" identifies a process through which the system gains heat, while "output" represents a heat loss from the system.

In a system heat budget (+) indicates input or heat gain, (-) signifies output or heat loss.

What is a heat budget?


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The heat from the Sun travels to the Earth in the form of short-wave radiation (solar radiation), which passes through the atmosphere without warming it.

Temperature is considered to be a measurement of the amount of heat in a particular body. Actually temperature is a measure of the average or mean motion of the molecules within a substance. But it is temperature that determine the flow of heat from one object to another. Heat will flow only from a body of higher to a body of lower temperature.

Heat vs TemperatureThe Sun is the origin of energy which causes variation of the temperature on Earth.

On striking the Earth some of the heat will be absorbed to warm the Earth.Some of the heat will be reflected from the Earth’s surface to the atmospheric boundaries to warm the atmosphere.


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The Sun heats the Earth and the Earth in its turn is responsible for heating the overlying air.

Temperature is a measurement of a state, while Heat is an energy quantity.

REMEMBER


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The name given to all the radiant energy we receive from the sun is "insolation".


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Insolation Processes

ReflectionAbsorptionScatteringTransmission


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If the sun's rays have little effect on the atmosphere on their passage through the air to the earth, the reflected radiation doesn't have any effect on the air.

We can consider that no significant change takes place in this energy as a result of reflection.

Reflection is important in that it lessens the amount of energy the earth would otherwise absorb and utilize in heating the air.

Reflection


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The amount of reflection depends on the color and smoothness of the surface.

Ocean surfaces will reflect far more insolation than land. Depending on the state of the sea, the ocean water will reflect from 40 to 50 % of all the insolation striking it.

The amount reflected by land varies considerably with locality, owing to the wide variation of the surface composition from place to place. Some substances will reflect a few per cent, while others, such as beach sand, will reflect a very large proportion of the sun's rays.

Reflection


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Dark, rough surfaces are the best absorbers of heat.

When a substance absorbs solar radiation (consisting of light and heat energy), the nature of this energy is changed almost completely into heat, increasing the heat content of the absorbing medium.

Since land surfaces differ so much as compared to the oceans, it follows that land temperatures will show much greater variation than water temperatures.

Absorption


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Absorption•Ozone absorbs UV radiation

•Water Vapor, CO2 absorb IR Radiation

Examples of gases which absorb radiation in the atmosphere

Absorption


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Transmittance

•Nitrogen and Oxygen are mostly transparent to both IR and UV radiation…but they do absorb higher forms of radiation…

Examples of gases that allow radiation to transmit through them

Absorption


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The better the absorber, the better the radiator.The better the absorber, the better the radiator.

Absorption


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•Aerosols and clouds scatter and reflect radiation

Back scattered light (same wavelength, same intensity)

Gas molecules more efficiently scatter the shorter wavelengths of visible light (blue and violet) than the longer wavelengths (red and orange).

ScatteringWhen light passes through a medium, containing particles less in diameter than the wavelength of the light, a portion of the light is scattered in all directions. This is called scattering.


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By the evening, when the sun is low on the horizon, all the blue light is scattered out leaving mostly red and orange light.

Blue skies are produced as shorter wavelengths of the incoming visible light (violet and blue) are selectively scattered by N2 and O2 – which are much smaller than the wavelength of the light.

Scattering


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Larger particles (haze, fog, or smog) scatter light more equally in all wavelengths. When there is a fog event the sky appears white because no wavelength of light is preferentially scattered.

Scattering


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This is the process of transfer of insolation after it has been absorbed. Heat energy may be transmitted from place to place by three different processes:Conduction: is transferring of heat between adjacent portion of matter by molecular contact without the transfer of the matter itself.Convection: is the processes of transmitting heat by actual motion of the heated material.Radiation: is the transmission of heat energy in wave-forms without the aid of a material medium. The energy of these waves is transferred into heat only when they strike bodies capable of absorbing heat.

Transmission


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visible light

+100% from Sun

-5% backscattered to space

-50% absorbed by Earth

-20% absorbed by clouds

-20% reflected from clouds

-5% reflected from land-sea

0 leftover

visible light

infrared light

Review of the Average Distribution of Incoming Solar Radiation


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The Heat Balance of the Atmosphere


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Ocean Heat Budget

• The sunlight reaching Earth– 1/2 oceans and land– 1/5 atmosphere

• The heat stored by the ocean– Evaporation and infrared radiation

atmosphere– Transported by current ameliorate Earth’s

climate development of ice age


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The Oceanic Heat Budget

Oceanic Heat Budget

Primary sources Secondary sources(+)

Solar radiation (+) Long-wave back radiation (-)

Air/Water heat transfer (+/-)

Evap./Condens. heat transfer (-/+)

Chemical/biological processes Hydrothermal activity

Current friction Radioactivity

Advection (+/-) Negligible for most applications


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• Heat budget– QT = QSW + QLW + QS + QL + QV

• The resultant heat gain or loss QT [wm-2]• Insolation QSW, the flux of sunlight into the sea• Net Infrared Radiation QLW, net flux of infrared radiation from

the sea• Sensible Heat Flux QS, the flux of heat out of the sea due to

conduction• Latent Heat Flux QL, the flux of heat carried by evaporated

water• Advection QV, heat carried away by currents

• Change in energy– ∆E = CpmDT

• Cp 4.0 103 J kg-1 C-1

The Oceanic Heat Budget


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Atmosphere and Ocean Heat Budgets

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