Physics, Atmospheric

the branch of meteorology that studies the physical regularities of processes and phenomena that occur in the atmosphere, including the processes and phenomena that determine the structure of the atmosphere. For example, atmospheric physics deals with the properties of the gases that constitute the atmosphere, the absorption and emission of radiation by the gases, the distribution of temperature and pressure, the evaporation and condensation of water vapor, the formation of clouds and precipitation, and the various forms of motion in the atmosphere.

Solar energy conversion and the thermal radiation of the atmosphere and underlying surface are studied by actinometry (in the broad sense of the term) and atmospheric optics. The latter also deals with various optical phenomena in the atmosphere, such as twilight, the colorful phenomena observed in the sky before sunrise and after sunset, halos, the color and polarization of the sky, and the visibility of objects. The study of atmospheric electricity is concerned with electrical phenomena in the atmosphere—that is, with lightning and other electrical discharges—and with the electrical properties of the atmosphere, such as conductivity, ionization, electric currents, space charges, and the charges of clouds and precipitation. Sound propagation and generation in the real atmosphere and the investigation of sound generation by acoustic methods are the subject of atmospheric acoustics. Atmospheric physics also encompasses cloud physics and the physics of the microprocesses that result in the formation of solid and liquid aerosols; these fields include the modification of atmospheric processes.

Atmospheric physics also studies the interaction of the atmosphere and the underlying surface—that is, the ocean or dry land—that occurs in the atmospheric boundary layer and results in the exchange of momentum, heat, and moisture. Turbulence in the atmosphere and hydrosphere plays a governing role in the interaction.

Processes in the upper atmosphere and the structure and dynamics of the upper atmosphere are investigated by the physics of the upper atmosphere or by aeronomy, a broader division of atmospheric physics that also studies the various chemical processes that occur in the upper atmosphere.

One of the fundamental problems of all the divisions of atmospheric physics is the development of a physical basis for the numerical modeling of various atmospheric processes. In this respect, the most important problem is parameterization, that is, the description of various small-scale processes by means of quantities that characterize average atmospheric conditions on larger scales that form the background against which the processes being studied develop. Such a description is necessary for computer simulations of atmospheric phenomena. For example, cumulus clouds, whose sizes are of the order of several kilometers, play an important role in atmospheric moisture and heat exchange, radiative transfer, and other processes. In numerical models, the effects of such clouds on radiation, heat exchange, and other atmospheric processes are parameterized, that is, expressed by means of temperature, wind, humidity, and other variables, which are given at specified points that form the three-dimensional grid of the numerical models; the distance between any two points is usually a few hundred kilometers.

Atmospheric physics also deals with the study of the atmospheres of the other planets, which contributes to a deeper understanding of the phenomena that occur in the earth’s atmosphere.