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LESSONS AND MODULES

Effect of the Sun's Energy on the Ocean and Atmosphere

Learning the Science

Only a small portion of the total energy, called radiation or electromagnetic radiation, emitted from the Sun actually reaches the Earth. Since energy can be neither created nor destroyed, it is then absorbed, scattered, or reflected. An object that fully absorbs and radiates all its energy is called a black body. A white body is an object that only reflects and does not absorb. The Earth is considered a gray body because it not only absorbs and radiates energy but it also reflects some of it. It does this to maintain a balance between the amount of energy coming in and the amount of energy being emitted back into space. The image below illustrates how this process occurs. The equilibrium is called the radiative balance. If it is achieved a body will maintain its temperature.

Earth's Energy Budget
Source: ERBE, Atmospheric Sciences Division, NASA LaRC.

According to the Wein's displacement law, the energy received from the Sun is at shorter wavelengths than the energy being emitted by the surface of the Earth. This is because the hotter a radiating body is, the shorter the wavelengths being radiated.

As the energy of the Sun reaches the atmosphere of the Earth, it interacts with the gases. The selectivity of the gases in this interaction is dependent on the wavelength of the energy and determines whether it is absorbed, reflected, or simply scattered. Greenhouse gases, such as carbon dioxide, water vapor, nitrogen oxides, methane, and ozone, absorb energy. Some of these gases such as water vapor, ozone, and small particles called aerosols can also reflect energy. Scattering, caused by areosols and other gas molecules, changes the energy's direction, in turn altering the overall energy budget.

It is mainly the flux of energy along with fluxes of moisture, momentum, and mass that determine the Earth's climate conditions. However, it is necessary to consider all components of the earth system including the hydrosphere, cryosphere (region of ice), biosphere, and lithosphere (region of rock), and their interactions when trying to simulate the real world using climate models.

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