Energy and Radiation

Net Radiation

Net Radiation is the difference between incoming (i.e., S and L↓) and outgoing components of radiation (S+D)a and L↑.

Q*= [(S+D) - (S+D)a] + L↓ - L↑

Net radiation can be positive, negative, or zero. Net radiation is positive 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.

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Figure 4.20 A net radiometer measuring incoming and outgoing radiation from an alpine snow pack. Measurements such as this aid in determining snow melt and the availability of water to fill community reservoirs like those near Boulder, CO. Courtesy Michael Ritter

Understanding net radiation and its distribution is fundamental to explaining many geographical patterns of the components of the earth system. Net radiation is the radiant energy that is available to do work within the earth system. This work is manifested in a variety of ways, from heating the air, to warming the surface, to causing water to evaporate.

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