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 fo r Medium-Range Weather Forecasts to calculate a mean global pressure to ser ve as a reference for an improved inverse barometer correction of altimeter data. These global pressure fields, available every 6 h on a 1/2 degree gr id, 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, wh ich was then used for an improved inverse barometer correction. The improve d correction reduces the standard deviation of mean sea level variations (r elative to an annual cycle and slope) by more than 20% when compared with s tandard inverse barometer correction and no correction at all. It also slig htly reduces the variance of sea surface height differences at crossover po ints. The impact of the improved correction on the mean sea level annual cy cle and slope is also not negligible.