What does isobar mean?
An isobar is a line connecting places that have the same atmospheric pressure, especially on a weather map. Isobars help forecasters understand air movement: where the lines are widely spaced, winds are generally light, while closely spaced isobars indicate a stronger pressure gradient and potentially stronger winds. The term comes from Greek roots meaning “equal” and “weight,” reflecting the early scientific association of atmospheric pressure with the weight of air. Although “isobar” is most common in meteorology, the same principle can describe lines of equal pressure in other fluids. It is distinct from an isotherm, which connects equal temperatures, and an isohyet, which connects equal amounts of precipitation. For anyone learning to read a synoptic weather chart, isobars are among the most useful basic features because they reveal the arrangement of pressure systems and help indicate where windy conditions may develop.
nounA line on a weather map joining points at which the atmospheric pressure is equal. More generally, any line representing equal pressure within a fluid.
- A line on a weather map or diagram connecting points of equal atmospheric pressure.
- A line in a fluid or other physical system connecting points of equal pressure.
"The forecast map showed tightly packed isobars over the region, indicating strong winds."
"Several isobars crossed the chart, with lower pressure toward the centre of the low."
"The laboratory plot uses isobars to show how pressure changes across the chamber."
The standard plural is used when referring to several lines of equal pressure on a map.
"The isobars curved around the edge of the high-pressure system."
On a weather map, every isobar is an equality line for pressure—and the closer they bunch together, the stronger the wind tends to be.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of isobar
Isobar was formed in the 19th century from Greek isos, meaning “equal,” and baros, meaning “weight,” a root also used in words such as barometer and barometry. In meteorological usage, the word developed the specific meaning of a line joining locations with equal atmospheric pressure. Its scientific context reflects the older conception of air pressure as the weight of the atmosphere pressing on a surface.
Related word forms
How isobar is actually used
Chiefly a technical term in meteorology and related physical sciences. In ordinary weather discussion, it is usually understood specifically as a line of equal atmospheric pressure on a map.
Easily confused with isobar
An isobar joins places with equal atmospheric pressure, whereas an isohyet joins places with equal precipitation.
An isobar represents equal pressure, while an isotherm represents equal temperature.