INTERANNUAL VARIATION OF ATMOSPHERIC MASS AND THE SOUTHERN OSCILLATION

Two reanalysis datasets, one generated by the Goddard Laboratory for A tmospheres for 1982-1993 and the other generated by the National Cente rs for Environmental Prediction for 1982-1995, are used to examine the relationship between the Southern Oscillation (SO) and the interannua l variation of atmospheric mass. Both reanalyses show that atmospheric mass increases (decreases) during the positive (negative) SO phase. A tmospheric mass consists of dry air and moisture. Since dry mass is co nserved, the interannual variation of atmospheric mass results from th e variation of water vapor pressure. Thus, global atmospheric hydrolog ical processes are analyzed to illustrate how the SO affects the inter annual variation of atmospheric mass. During the positive (negative) S O phase, water vapor is converged (diverged) toward (out of) the centr al-eastern tropical Pacific [where sea surface temperatures (SSTs) are higher (lower) than normal] to maintain (suppress) cumulus convection in that area. An anomalous east-west Walker circulation straddling th e Dateline is driven by the anomalous cumulus convection in this regio n to create positive (negative) surface pressure anomalies over the we stern tropical Pacific-Indian Ocean, which result in an increase (decr ease) in atmospheric mass.