The Tropical West Pacific Convection and Cold Surges in the Southern South America

MULLER, GABRIELA VIVIANA; AMBRIZZI, TÉRCIO

Beijing, China

Conferencia; IAMAS; 2005

A multilevel primitive equation model is used to examine a possible influence of the convection in the tropical west Pacific and frost events in the region called Pampa Humeda in the center-east Argentina during austral winter. The sensitivity of the phase and amplitude of the quasi-stationary Rossby wave response to the heating anomaly over the tropical west Pacific ocean is examined through numerical simulations. The model was integrated for 15 days and perturbated with a heating source coincided with  the OLR anomalies observed in winter (JJA) composites These composites are separated in two groups, where the numbers of generalized frost events were above (AA) or below (BA) average, considering the standard deviations. The composite analyses suggest a clear connection between tropical convection and cold surges. It seems that there is an interaction between the subtropical and subpolar wave guides creating the right wave phase for the trough amplification over the Pampa Humeda region. Our numerical results showed that there is a convergence pattern of the subtropial and subpolar jets in years with generalized frost events above the average (AA). Therefore, synoptic systems are conducted through the continent, with cold air advection from the south-southwest direction and possible occurrence of frost events. During BA events there is only the presence of the subtropical jet. In terms of the wave theory and from comparison of the observational and numerical results it is suggested that frost events may occur when the subtropical and subpolar waveguides are in phase, which allow the incursion of large amplitude trough from the South part of South America.