Figure 4.8
Visualizing isobars. (A) In this scenario, atmospheric pressure (molecular density) decreases across a region from left to right. Air pressure is quantified using a barometer, and a partition is drawn for every four millibars of pressure change. (B) When the top three-dimensional image is transferred onto a flat two-dimensional map, the partitions become lines of equal pressure, or isobars. Air pressure at location 1 is between the 1016 mb and 1020 mb isobars. Location 2 is on the 1012 mb isobar. Therefore, the pressure gradient runs from location 1 to location 2.