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1. Introduction
Large scale link between the interannual variations of ocean surface temperatures in the equatorial central and eastern Pacific regions to persistent regional and global atmospheric anomalies has been demonstrated after many scientific works in the last decade.
A large scale abnormal warming in the equatorial Pacific known as El Niño, refers to the large scale atmospheric effects related to the surface ocean warming. During the El Niño episodes lower than normal pressures are observed in the eastern tropical Pacific and higher pressures are found over western Pacific as Indonesia and northern Australia. These conditions characterize the warm phase of the Southern Oscillation (SO), which is often referred to as an El Niño Southern Oscillation (ENSO) episode.
During periods when ocean surface temperatures are colder (the cold phase of the SO, know as La Niña), lower than normal pressures are found over western Pacific region and higher pressures are observed over the eastern tropical Pacific.
During a warm episode winter, mid-latitude low pressure systems tend to be more strong than in normality in the the Gulf of Alaska region. These systems pump abnormally warm air into western Canada, Alaska and the extreme northern portion of the contiguous United States. Storms also tend to be more vigorous in the Gulf of Mexico and along the southeast coast of the United States resulting in wetter conditions than normal in that region.
During cold episodes, colder ocean temperatures in the equatorial central Pacific act to inhibit the formation of rain-producing clouds over that region. Wetter conditions are also observed over southeastern Africa and northern Brazil, during the northern winter season. Drier conditions during cold episodes are observed along the west coast of tropical South America, and at subtropical latitudes of North America (Gulf Coast) and South America (southern Brazil to central Argentina) during their respective winter seasons
During warm and cold episodes the normal pattern of tropical precipitation becomes altered affecting the tropical atmospheric circulation features. Also, during warm and cold episodes extratropical storms and frontal systems follow paths that are significantly different from normal, resulting in persistent temperature and precipitation anomalies in many different regions
The relation of that warm and cold episodes in the central Pacific with a highly precipitation anomalies persistence pattern in consistence with different episodes from latitudes corresponding to North America Wang H. et al. (1999), Barsugli et al. (1999), Bell et al. (1999), up to South America and specially from southern Brazil to the central Argentina Mechoso C. and Iribarren (1992), Lenters and Cook (1995), Harzallah et al (1996),Grimm et al. (2000), Ropelewski and Halpert (1987; 1989), Halpert and Ropelewski (1992).
Specifically a general description ENSO episode related with seasonal mechanism was found in Aceituno, P (1988), Tziperman et al(1997) and many others. Concerning to the upper-tropospheric circulation features that accompany extreme phases of the Southern Oscillation are discussed in the work of Arkin, 1982.
Evidence of ENSO teleconnection impacts over local parameters such precipitation and TCC in South America are demonstrated by:
- Pinker and Laszlo (1992), studied the variability of solar irradiance of Amazon basin.
- Piacentini R. (1998) quantifying the nebulosity fraction reduction in the region of Rio de la Plate basin including Buenos Aires.
- P.Ristori et al, 2000 ILRC 2000 over Bs. As. (34º36’S 58º26’W) region quantifying the temporal evolution of teleconnection coupling evolution in time during the last ENSO episodes (1997//1998).
- Grimm et al (2000); was detected and calculated the coherence rainfall response to the El Niño and La Niña events from 1957 to 1991.
- Mechoso et Iribarren (1992); was calculate the streamflow variability in Uruguay country from 1901 to 1989 and detecting the ENSO phases.
In this work we present a geographical "coherence zone" identification of the region having the major coupling variability driving by ENSO events in their different phases: Niño (+1), La Niña (-1), Normality (0) scrutiny from 1980 to 1999 period. Starting in section 2 with a description of data base used and the methodology utilized; in the section 3 we present the principal results for this application. Finally, with the objective to achieved the Air Quality implications we compute the local influence over total incoming visible radiation flux and their coupled variability over Mixed Layer Atmospheric Boundary Layer Height, as a local parameter, for the last strong ENSO event (1997//1998). Finally a summary and concluding remark are presented in section 4.