# Isobars

Isobars of a weather front system during a hurricane over the British Isles

An isobar (from ancient Greek ἴσος ísos 'equal' and βάρος báros 'pressure') is an isoline of the same pressure (  ). ${\ displaystyle p = {\ text {const.}}}$

In meteorology in particular , the isobars on meteorological ground weather maps indicate places with the same air pressure . Measured values ​​from neighboring locations are used to determine the locations with this air pressure. All locations determined in this way result in a closed line (curve). The measure on the isolines is given in hPa . A soil weather map shows several isobars for an area, i.e. in addition to the isobars for 980 hPa also those for 985 hPa etc. The distances between the isobars are thus, conversely, a measure of the pressure gradient.

The direction of the wind can be estimated from the course of the isobars, and the wind strength can be estimated from their distance ( estimation of the wind speed ): If the isobars are closer together, the pressure gradient is greater and thus the wind is stronger.

The information on air pressure in weather maps always relate to sea ​​level . The values ​​of the measuring stations must be corrected with the help of the reduction to sea level . Unless otherwise stated, isobars are generally drawn for an air pressure of 1000 hPa and values ​​at a distance of 5 hPa. In England, the USA, Canada and other Anglo-Saxon countries, intervals of 4 hPa are common.

The use of isobars in meteorology goes back to Alexander Buchan (1829–1907).