micrometeorology

The study of weather conditions on a small scale, as in the area immediately around a building, smokestack, or mountain.

The study of small-scale meteorological processes associated with the interaction of the atmosphere and the Earth's surface. The lower boundary condition for the atmosphere and the upper boundary condition for the underlying soil or water are determined by interactions occurring in the lowest atmospheric layers. Momentum, heat, water vapor, various gases, and particulate matter are transported vertically by turbulence in the atmospheric boundary layer and thus establish the environment of plants and animals at the surface. These exchanges are important in supplying energy and water vapor to the atmosphere, which ultimately determine large-scale weather and climate patterns. Micrometeorology also includes the study of how air pollutants are diffused and transported within the boundary layer and the deposition of pollutants at the surface.

In many situations, atmospheric motions having time scales between 15 min and 1 h are quite weak. This represents a spectral gap that provides justification for distinguishing micrometeorology from other areas of meteorology. Micrometeorology studies phenomena with time scales shorter than the spectral gap (time scales less than 15 min to 1 h and horizontal length scales less than 2–10 km or 1–6 mi). Some phenomena studied by micrometeorology are dust devils, mirages, dew and frost formation, evaporation, and cloud streets. See also Air pollution; Atmosphere; Mesometeorology.

Much of the early understanding of micrometeorology was obtained by studying conditions in large, flat, uniform areas that are relatively simple situations. Micrometeorologists have turned their attention to more complex situations that represent conditions over more of the Earth's surface. The micrometeorology of complex terrain, that is, hills and mountains, is important for air pollution in many towns and cities and for visibility in national parks and for locating wind generators. Another interest is the study of micrometeorology in areas of widely varied surface conditions. For instance, several different crops, dry unirrigated lands, lakes, and rivers may be located near one another. In these cases it is important to understand how the micrometeorology associated with each of these surfaces interacts to produce the overall heat and moisture fluxes of the region so that these areas can be correctly included in weather and climate forecast computer programs. See also Climatology; Mountain meteorology; Weather forecasting and prediction.

Microscale meteorological features are too small to be observed by the standard national and international weather observing network. Generally, micrometeorological phenomena must be studied during specific experiments by using specially designed instruments. Instruments used to study turbulent fluxes must be able to respond to very rapid fluctuations. Special cup anemometers are made from very light materials, and high-quality bearings are used to minimize drag. Other anemometers use the speed of sound waves or measure the temperature of heated wires to measure wind. Tiny thermometers are used, so that time constants are short. Instruments are usually placed on towers or in aircraft, or are suspended in packages from tethered balloons. Instruments have been developed that can measure turbulence remotely. Wind speed and boundary-layer convection can be measured with Doppler radar, lidar devices using lasers, and sodar (sound detection and ranging) using sound waves. See also Atmospheric acoustics; Lidar; Meteorological instrumentation; Meteorological radar; Meteorology.

The study of small-scale meteorological phenomena operating near the ground surface, such as the investigation of climates within a field of grain or in a forest.

Study of the climate of a microhabitat or a microclimate.