isobar

 

(meteorology and climatology)

A curve along which pressure is constant. Leading examples of its uses are in weather forecasting and meteorology. The most common weather maps are charts of weather conditions at the Earth's surface and mean sea level, and they contain isobars as principal information. Areas of bad or unsettled weather are readily defined by roughly circular isobars around low-pressure centers at mean sea level. Likewise, closed isobars around high-pressure centers define areas of generally fair weather. See also Air pressure.

A principal use of isobars stems from the so-called geostrophic wind, which approximates the actual wind on a large scale. The direction of the geostrophic wind is parallel to the isobars, in the sense that if an observer stands facing away from the wind, higher pressures are to the person's right if in the Northern Hemisphere and to the left if in the Southern. Thus, in the Northern Hemisphere, flow is counterclockwise about low-pressure centers and clockwise about high-pressure centers, with the direction of the flow reversed in the Southern Hemisphere. See also Geostrophic wind; Weather map.

Isobar (nuclear physics)

One of two or more atoms which have a common mass number A but which differ in atomic number Z. Thus, although isobars possess approximately equal masses, they differ in chemical properties; they are atoms of different elements. Isobars whose atomic numbers differ by unity cannot both be stable; one will inevitably decay into the other. See also Electron capture; Radioactivity.

(ī'səbär') or isobaric line (ī'səbăr'ĭk) , line drawn on a weather map through points of equal atmospheric pressure. Isobars are used to define cyclones (low-pressure regions) and anticyclones (high-pressure regions). Weather maps are designed to depict the horizontal pressure distribution across an area of land, but atmospheric pressure also varies vertically, i.e., with altitude. To eliminate any consideration of the vertical variations of pressure, the barometer readings at all stations are reduced to their corresponding sea-level pressures before the isobars are drawn.

The word isobar derives from the two ancient Greek words, ισος (isos), meaning 'equal', and βαρος (baros), meaning 'weight'.

• In meteorology, thermodynamics, and similar science (and engineering), an isobar is a contour line of equal or constant pressure on a graph, plot, or map. (For further discussion, see under Contour line)

• In nuclear physics, two nuclides with the same mass number are called isobars. For example, boron-12 and carbon-12 are isobars.

• Isobar has also occasionally been used as a synonym for a heat pipe.

• Isobar is the title of a 2007 science fiction film.

• Isobar is an international network of digital marketing agencies.

See also

• Isosurface
• Isobaric process

Similar terms

• Isotope - one of multiple varieties of the same element of different atomic masses
• Isotone - one of multiple nuclides with equal numbers of neutrons
• Isomer - one of multiple molecules with the same formula
• Nuclear isomer - a nuclide in a neutral state (i.e., containing more energy, but with no change in number of protons and neutrons)

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