surfaces of equal air pressure in the atmosphere.
The relative location of isobaric surfaces gives an idea of the spatial distribution of air pressure. In a cyclone (that is, an area of reduced pressure) an isobaric surface is a concave surface and in an anticyclone (that is, an area of increased pressure) it is convex. The slope of isobaric surfaces determines wind speed: the greater the slope of the isobaric surfaces, the greater the wind speed, all other conditions being equal. The intersection of isobaric surfaces with a horizontal plane (at sea level and other level surfaces) produces isobars.