Meteorology · Barometer — Sea-Level Reduction
Why are barometer readings reduced to sea level before plotting on a synoptic chart?
- ASo pressures measured at different elevations are directly comparable, isolating the horizontal pressure pattern✓ Correct
- BTo convert millibars to inches of mercury
- CTo remove the effect of temperature on the instrument
- DTo account for the tide
Explanation
Pressure decreases with height, so readings from instruments at different elevations must be reduced to a common datum (sea level) before they can be compared and isobars drawn. Otherwise elevation differences would mask the real weather pattern.
Authority: WMO; Bowditch (Pub. No. 9), pressure reduction
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