Problems with the Mean Sea Level Pressure Field over the Western United States

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Abstract Reduction of station pressure to mean sea level (MSL) is a difficult procedure. In general, the temperature structure of the fictitious air column between station height and MSL is not known and has to be estimated somehow. Normally, station pressure is reduced to MSL only for stations with relatively low elevations above sea level (ASL). At higher stations, station pressure is usually converted to the height of the closest standard pressure surface. In the United States, however, station pressure is reduced to MSL for stations as high as 2000 m ASL. In order to reduce the amplitude of the annual MSL pressure variation at stations situated above 305 m ASL (hereinafter referred to as “plateau stations”), a so-called plateau correction is applied at these stations. The correction increases reduced MSL pressure when the actual temperature at the station is greater than the yearly mean temperature at the same station, and vice versa. The correction can therefore change both magnitude and direction of...