A climatology of tropical instability waves using the ERS-1 and -2 scatterometers

The strong coupling of the atmospheric boundary layer to oceanic tropical instability waves (TIW) results in a signature of these waves in the surface wind field. Surface winds derived from the ERS-1 and -2 scatterometers enable the development of a climatology of these waves. Although the sparsity of this data introduces sampling errors, the waves are clearly visible when they are present and their phase speeds are clearly discernible. The ERS-1 and -2 scatterometers have been in operation since 1991, and therefore provide us with a look at these waves on annual and interannual time scales. Here ERS-1 and -2 data are analyzed in conjunction with sea surface temperatures (SST) illuminating the behavior of TIWs. On annual time-scales, the waves regularly appear in May at about 95°W and propagate westward along the SST front that marks the northern edge of the Pacific SST cold tongue. The western-most extent of these waves varies considerably from year to year as does the cold tongue. On the interannual time scale, TIW activity is strongest during the cold phase of the ENSO cycle (La Nina) when the cold tongue is most pronounced; the waves are nonexistent during the warm phase of ENSO (El Nino) when the SST front is weak