Global fluctuations in the distribution of atmospheric mass.

Two global data sets have been analyzed to determine the interannual variability of the zonal mean mass distribution. The 1st is a National Meteorological Center (NMC) global data set of sea level pressures beginning in December 1977 and surface pressures beginning in April 1979. The 2nd is an 11yr (1972-1982) hybrid set of sea level pressures from the Australian southern hemisphere and US Navy northern hemisphere analyses. The 2 sets are compared and evaluated by seeing how well they satisfy the constraint of conservation of mass. Anomalies in total mass due to changes in water vapor content of the atmosphere are lost in the data problems. Several inhomogeneities or discontinuities are found and are identified either with changes in analysis procedures in both data sets or the introduction of new orography and operational models at NMC. Consequently only limited periods of data are suitable for determining the dominant modes of variability. Nevertheless, hemispheric mean anomalies in mass in one hemisphere tend to be mirrored in the other, and it is clear that previously deduced fluctuations in hemispheric mean mass are mostly real. Predominant modes of variability of zonal means reveal systematic exchanges of mass 1) almost entirely confined within each hemisphere in isolation, 2) between the extratropics of each hemisphere with little impact on the tropics as an antisymmetric mode.-from Authors