mean sea level

From Glossary of Meteorology
(Abbreviated MSL; popularly called sea level.) The arithmetic mean of hourly heights observed over some specified period.

In the United States, mean sea level is defined as the mean height of the surface of the sea for all stages of the tide over a 19-year period. Selected values of mean sea level serve as the sea level datum for all elevation surveys in the United States. In meteorology, mean sea level is used as the reference surface for all altitudes in upper-atmospheric work; in aviation it is the level above which altitude is measured by a pressure altimeter. Along with mean high water, mean low water, and mean lower low water, mean sea level is a type of tidal datum.
Compare half-tide level, still-water level.

Copyright 2024 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact permissions@ametsoc.org. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.