Intercomparison of four different Southern Hemisphere sea level pressure datasets

Four different monthly sea level pressure (MSLP) datasets for the Southern Hemisphere (SH, south of 15°S) are intercompared for the 1961–2000 period, contrasting the differences in decadal-average pressure and differences between correlations for the 1961–80 (pre-satellite measurement era) and the 1991–2000 (post-satellite) period. Agreement is very dependent on the locations in the observing network, and this becomes even clearer for the two decades (1961–80) before the satellite era. Away from the station locations it is impossible to say which provides the ‘best’ decadal average MSLP values, due to assumptions made in the dataset derivation. Improved reanalyses will be undertaken in the next few years, but they are only likely to provide the true decadal average values of MSLP for the 1961–80 period if a much higher percentage of observations made for this period are digitized, and provided they are quality controlled, assessed for homogeneity and given higher priority within the reanalysis system.