Noun

1. A line drawn on a map or chart connecting places of equal or constant pressure.
2. Either of two nuclides of different elements having the same mass number.
3. A set of points or conditions at constant pressure.

Usage notes

• Meteorology

  In meteorology, 'isobar' most often refers to a line drawn through all points of equal atmospheric pressure along a given reference surface, such as a constant height surface (notably mean-sea-level on surface charts); the vertical plane of a synoptic cross section, or a map of the air unaffected by surface heating or cooling. The pattern of isobars has always been a main feature of surface chart analysis. Until recently it was standard procedure to draw isobars at 3-millibar intervals. However, the advent of constant pressure charts for upper-air analysis has brought about the use of 4-millibar intervals to simplify the conversion from surface isobars to 1,000-millibar contour lines.

See also

• isotone
• isotope
• isotherm
• isochore
• isopleth
• adiabat