Radiative Processes in the Lower and Middle Atmosphere

The circulation and dynamics of the Earth’s atmosphere depend mainly on the magnitude and distribution of the net radiative heating of the Earth atmosphere system. In the troposphere, the net diabatic heating rate is dominated by the imbalance between the transfer of heat from the surface and the thermal emission of radiation to space. Latent heat is the major component of the flux from the surface to the atmosphere, and clouds play a major role in the emission of radiation to space.

In the stratosphere, the net heating depends solely on the imbalance between local absorption of solar UV radiation and infrared radiative loss. In this region, ozone is the principal absorber and carbon dioxide is the dominant emitter. Infrared emission by ozone and water vapor, and solar radiation absorption by water vapor, molecular oxygen, carbon dioxide, and nitrogen dioxide play secondary roles. The distribution of the radiative sources and sinks due to the above gases exerts a zeroorder control on the large-scale seasonally varying mean temperature and zonal wind fields of the stratosphere (Andrews et al. 1987). These radiative processes are therefore significant to understand the stratosphere–troposphere interactions.

In this chapter, we will discuss the basic principles of radiation, solar radiation, and their processes in the stratosphere and troposphere. Detailed information on the radiative processes in the atmosphere is available elsewhere (Chandrasekhar 1950, Goody 1964, Kondratyev 1972, Liou 1980, Paltridge and Platt 1976, Smith 1985, etc.).