Isobar

Origin

From Ancient Greek ἴσος (isos, "equal") + βάρος (baros, "weight")

Full definition of isobar

Noun

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

Usage notes

(meteorology)

In meteorology, the term isobar most often refers to a line drawn through connected points of equal atmospheric pressure on 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 layer of the air unaffected by surface heating or cooling. The pattern of isobars has always been a main feature of surface chart analysis. (See ) 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.