regions of decreased and increased atmospheric pressure; parts of the isobaric field of the atmosphere. The main isobaric fields—cyclones (low-pressure fields) and anticyclones (high-pressure fields)—are shown on ground pressure-distribution charts by closed isobars—that is, lines that connect points of equal pressure. Isobaric fields with open isobars may also be found—low-pressure troughs and high-pressure ridges. Most frequently these are some-what isolated peripheral sections of cyclones and anticyclones. Another type, the saddle, is a region in which two cyclones and two anticyclones intersect each other. Isobaric fields vary in size; however, they usually cover areas as large as continents and oceans or major portions thereof. Isobaric fields shift, change in size and intensity, reform, and vanish continuously. They are accompanied by specific systems of air currents (winds), temperature distribution, cloud cover, precipitation, and so on.
S. P. KHROMOV