Tropical perturbations in the Eastern Pacific and the Precipitation field over North‐Western Mexico in relation to the enso phenomenon

Abstract

AbstractMonthly time series of the number of tropical perturbations (TP) for the eastern tropical Pacific Ocean, the Southern Oscillation Index (SOI), the north‐eastern tropical sea‐surface temperature (SST), and the precipitation field over north‐western Mexico for the period 1966–1988 are analysed by using power spectral techniques. It is found that a significant coherence exists at the frequency bands of 0.015–0.025 cycles per month and 0.035–0.040 cycles per month. These signals are associated with the El Niño/Southern Oscillation (ENSO) and the Quasi‐Biennial Oscillation (QBO) phenomena, respectively. As reported elsewhere, fewer tropical storms over the Atlantic and western Pacific Oceans tend to be associated with negative values of the SOI (or positive anomalies of the eastern Pacific SST); however, for the eastern Pacific, only the period 1966–1979 coincides with the above conclusion. The period 1980–1987, with two observed ENSO phenomena, shows an above normal number of TP coincident with negative values of the SOI and positive SST anomalies. Briefly, the controlling mechanisms lie in the atmospheric and oceanic interactions. That is, during the period 1966–1979, the thermal potential was relatively weak, while for the period 1980–1988 the thermal potential was stronger, with more frequent tropical cyclone formation. The summer precipitation field over the Sonoran Desert, Mexico, is largely influenced by the nearby presence of eastern Pacific tropical perturbations, especially during the ENSO years, while summer precipitation over the Sierras (south‐east of the Sonoran Desert) always shows an influence from both the Atlantic and Pacific atmospheric phenomena.