THE COADS SEA-LEVEL PRESSURE SIGNAL - A NEAR-GLOBAL EL-NINO COMPOSITEAND TIME-SERIES VIEW, 1946-1993

Using GOADS data for the period 1946-1993, the near-global sea level p ressure (SLP) patterns associated with interannual variability and the climatological seasonal march are discussed. A particular focus conce rns the patterns associated with the two years before and after the So uth American sea surface temperatures rise (El Nino). The ten El Nino events in this record are composited and the robustness of the feature s of this composite is tested. Many features of the composite are quit e robust; they occur during most El Nino events and are infrequent dur ing non-El Nino periods. The most robust feature is an area of negativ e SLP anomaly (SLPA) in the eastern equatorial Pacific during Year(0) of the composite. This feature exceeds significance thresholds during every El Nino year and never during non-El Nino years; it correlates b etter with central Pacific SST variability than does the SOI. A west-c entral North Pacific positive SLPA, occurring late in Year(0) and last ing into the spring of Year(+1), is the second most robust feature. St rong SLPA signals occur in the eastern South Pacific and around Austra lia in many events, but the behavior varies greatly from event to even t. Some events show interesting signals in the Indian and Atlantic Oce ans, but the behavior is not sufficiently general to be a statisticall y meaningful element of the composite. The largest signals in the comp osite occur in the eastern equatorial and west-central North Pacific a nd not in the Southern Hemisphere. Thus, the large-scale SLP variation s associated with El Nino periods are not dominated by the classical S outhern Oscillation. Little evidence is found for phase propagation of the signal in El Nino years. Although several features of the composi te occur during the same season in each El Nino period, so that the ma in signals are ''phase locked'' to the seasonal cycle, the patterns of variability have Little in common with the patterns of the seasonal m arch of SLP.