METEOROLOGY

scientific discipline concerned with atmospheric phenomena, particularly of the troposphere and lower stratosphere. Meteorology entails a systematic study of short-termthat is, day-to-dayvariations in temperature, humidity, air pressure, wind, cloud cover, and precipitation, along with their causes. It provides the basis for weather forecasting. Meteorology is closely related to, but distinct from, climatology (q.v.), which deals with weather conditions in a given area over an extended period of time (from a month to many millions of years). Meteorology is divided into two major branches, dynamic and synoptic. Dynamic meteorology deals primarily with the motions of the atmosphere and the physical processes involved in air flow. Research in the field involves the extensive use of computer models of general global circulation and of small-scale motion systems such as tornadoes and hurricanes. These mathematical models contribute much to the understanding of the physics and structure of the lower atmosphere. Synoptic meteorology concentrates on atmospheric phenomena that are directly associated with weather. It derives its name from the synoptic method, in which simultaneous observations of atmospheric conditions for a specific time are plotted on a map for a broad area whereby a general view of the weather in that area is attained. The observations are routinely collected from a worldwide network of facilities, including ground-based radars and remote-sensing systemse.g., balloon-borne radiosondes and Earth-orbiting meteorological satellites. Synoptic meteorologists use data from these facilities to make short-range forecasts of local weather. Such forecasts project atmospheric conditions for time periods of a few hours to 12 hours in advance. For extrapolating weather for a longer range and perhaps a larger area, they employ numerical weather prediction models consisting of mathematical representations of the physical conservation laws of motion, heat, mass, and moisture in the form of nonlinear, partial differential equations. Such numerical models, integrated with high-speed supercomputers, make it possible to accurately predict pressure fields, temperature anomalies, and, to a lesser degree, precipitation, fairly accurately five to seven days in advance. Numerical forecasting is in large part based on the principles and methodology of dynamic meteorology.