isobar

isobar or isobaric line , line drawn on a weather map through points of equal atmospheric pressure. Isobars are used to define cyclones (low-pressure regions) and anticyclones (high-pressure regions). Weather maps are designed to depict the horizontal pressure distribution across an area of land, but atmospheric pressure also varies vertically, i.e., with altitude. To eliminate any consideration of the vertical variations of pressure, the barometer readings at all stations are reduced to their corresponding sea-level pressures before the isobars are drawn.

isobar Line on a weather map connecting points of equal pressure, either at the Earth's surface or at a constant height above it. The patterns of isobars depict the variation in atmospheric pressure, showing areas of high and low pressure on the map.

isobar Line on a weather map connecting points at the same atmospheric pressure. On surface charts the values are ‘reduced’ to sea level. Such isolines are drawn at a given interval in millibars. Contours of isobaric surfaces may be drawn to represent surfaces in the upper atmosphere composed of points at the same pressure.