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

Abstract

Monthly 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 northwestern 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 00354040 cycles per month. These signals are associated with the El Niiio/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 SO1 (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 T P coincident with negative values of the SO1 and positive SST anomalies. Briefly, the controlling mechanisms lie in the atmospheric and oceanic interactions. That is, during the period 19661979, 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.

Distinguishing Pronounced Droughts in the Southwestern United States: Seasonality and Effects of Warmer Temperatures

“…Pacific SST anomalies associated with ENSO and the PDO tend to influence rainfall during this time of year in contrasting circumstances to that of winter and early spring precipitation. Pacific SSTs also may influence late summer and early autumn precipitation associated with dissipating tropical cyclones from the eastern Pacific Ocean, as a less favorable environment for cyclone development tends to happen during El Niñ o events or the warm phase of the PDO (Smith 1986;Reyes and Mejía-Trejo 1991;Englehart and Douglas 2001). Warm SST anomalies along the equator in the eastern and central Pacific Ocean and the coast of western North America, in combination with cool SST anomalies in the north-central Pacific Ocean, produce teleconnection patterns that favor westerly upper-level winds that inhibit moisture transport into the Southwest and a weaker and more southwardly displaced monsoon ridge (Castro et al 2001(Castro et al , 2007.…”

The Influence of Eastern Pacific Tropical Cyclone Remnants on the Southwestern United States

“…Tropical cyclones strongly affect precipitation totals along the coast of Mexico (Reyes and Mejía-Trejo 1991;Englehart and Douglas 2001;Já uregui 2003;Larson et al 2005). Although the tropical cyclone-strength winds typically diminish rapidly upon making landfall, these systems still contain a large quantity of tropical moisture and, upon interaction with mountainous terrain, have the potential to drop copious amounts of precipitation in localized areas.…”

Correlations between sea‐surface temperatures and warm season streamflow in northwest Mexico

“…2. During El Niño (La Niña), large-scale modulation of the eastern Pacific cross-equatorial transport results in a southward (northward) displacement of the intertropical convergence zone (Cavazos and Hastenrath, 1990;Reyes and Mejía-Trejo, 1991). Subsidence over southern portions of México is also enhanced (decreased) as a result of increased (decreased) convection in the eastern tropical Pacific during warm (cool) ENSO events (Magaña et al, 1999;Mo and Peagle, 2000;Higgins and Shi, 2001).…”