DEPARTURES FROM THE LOCAL INVERSE BAROMETER MODEL AT PERIODS OF 5 DAYS IN THE CENTRAL SOUTH-ATLANTIC

Tide gauge data from Ascension and St. Helena in the central South Atl antic, supplemented by altimeter data from the TOPEX/POSEIDON mission, suggest that the local inverse barometer (LIB) model for the forcing of sea level variability by means of air pressure changes is not appli cable within a narrow band of the variability spectrum with periods of approximately 5 days. This is in contrast to other sections of the wi der frequency band spanning approximately 0.05 to 0.5 cycles/d, wherei n the data are either consistent with approximate LIB response or at l east suggest no departures from the LIB model of similar magnitude. Th ese results have similarities to findings from Pacific gauges obtained over a decade ago, but so far, no comparisons have been to data from other ocean areas. They are also qualitatively similar to predictions for the region from a recent global barotropic numerical model. The an omalous part of the spectrum coincides in frequency with the Madden an d Julian (1972, 1973) 5-day pressure wave in the atmosphere. If that g lobal scale forcing is responsible for both the Atlantic and Pacific d epartures from the LIE model around 5 days, then similar features shou ld be observable in tide gauge data from other tropical areas.