Barometric Pressure Variations Associated with Eastern Pacific Tropical Instability Waves*

Barometric pressure, surface temperature, and wind time series in the eastern equatorial Pacific are analyzed to determine if oceanic tropical instability wave (TIW) sea surface temperature variations cause barometric pressure gradients large enough to influence the atmospheric boundary layer. During the study period from April 2001 to September 2002, 11 TIWs propagated westward past 110!W, causing a spectral peak at 20–30 days in the sea surface temperature (SST) meridional difference between 2!N, 110!W and 0!, 110!W. Likewise, the meridional pressure difference also had a spectral peak in the 20–30-day TIW band. Cross-spectral analysis shows that within the TIW band, SST-induced pressure variations were roughly "0.1 hPa !C"1 in magnitude. The resulting pressure gradient force is comparable in magnitude to other terms in the meridional momentum balance. Implications about the role of the boundary layer capping in the adjustment to SST forcing are discussed.