Effects of Global Mean Atmospheric Pressure Variations on Mean Sea Level Changes from TOPEX/Poseidon

The authors used meteorological pressure fields from the European Centre for Medium-Range Weather Forecasts to calculate a mean global pressure to serve as a reference for an improved inverse barometer correction of altimeter data. These global pressure fields, available every 6 h on a \textonehalf degree grid, enabled the extraction of the dominant mean pressure signals. Then, the effect of an improved inverse barometer correction on TOPEX/Poseidon mean sea level variation was estimated. Different low-pass smoothings of global mean pressure were used with cutoff frequencies ranging from (40 to 2 days)-1. Best results were obtained with the (2 days)-1 cutoff frequency, which was then used for an improved inverse barometer correction. The improved correction reduces the standard deviation of mean sea level variations (relative to an annual cycle and slope) by more than 20\% when compared with standard inverse barometer correction and no correction at all. It also slightly reduces the variance of sea surface height differences at crossover points. The impact of the improved correction on the mean sea level annual cycle and slope is also not negligible.