Definition: Isobars are lines of equal atmospheric pressure drawn on a meteorological map. Each line passes through a pressure of a given value, provided certain rules are followed. The rules for drawing isobars are-
- Isobar lines may never cross or touch.
- Isobar lines may only pass through pressures of 1000 + or - 4. In other words, allowable lines are 992, 996, 1000, 1004, 1008, and so on.
- The atmospheric pressure is given in millibars (mb). One millibar = 0.02953 inches of mercury.
- Pressure lines are usually corrected for sea level so any differences in pressure due to altitude are ignored.
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