isobar

in atmospheric chemistry
https://doi.org/10.1351/goldbook.I03260
Lines on a plot joining points of equal barometric pressure in the atmosphere.
Source:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2198 (https://doi.org/10.1351/pac199062112167)