✍ Scribed by B. Mendoza; R. Pérez Enríquez; M. Alvarez-Madrigal
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We studied the occurrence of ENSO (El Nifio-Southern Oscillation) events in relation to solar activity conditions and we found that the events are distributed in two populations, one that could be associated with low latitude coronal holes which occur along the ascending phase of the cycle and the other one which could be related to polar holes present at the end of the descending phase. As highly anomalous solar activity, in terms of flares and coronal holes, occurred in March of this year, we propose that an ENSO event is likely to occur by the end of the year.
The phenomenon known as E1 Nifio is characterized by the presence in the equatorial and Peruvian coasts of an abnormally warm stream that seems to be related to the southern Oscillation. Such a stream appears generally in January and persists for approximately three months. There is little doubt that the event E1 Nifio-Southern Oscillation (ENSO) is produced by instabilities in the ocean-atmospheric system (Philander, 1986;Graham, Michaelsen, and Barnett, 1987). In this sense, several coupled ocean-atmospheric models have been proposed (Philander, Yamagata, and Pacanowski, 1984;Lau, 1985;Anderson, 1985; Hirst, 1986)providing a considerable insight into the mechanism of growing and oscillating modes of the coupled system. Cane, Zebiak, and Dolan (1986) presented a model taking into account the oceanatmosphere interaction, whose predictability is limited by its neglect of atmospheric disturbances not attributable to air-sea coupling. It is the existence of a factor external to the air-sea system which leads us to think of the solar variability as a most obvious candidate for exerting such an influence, added to the fact that positive correlations between solar related events and geomagnetic and/or meteorological phenomena have been found (see, for instance, Wilcox and Scherrer, 1981, Bates, 1981;Wu, Dryer, and Han, 1983; Lundstedt, 1984).
In fact, if we look at the solar activity data for the past 50 years we notice that ENSO events seem to be associated with anomalous solar activity. Such is the case of the unsually high activity associated with the flares of 1942, 1956, 1972, and 1985. Solar flares as well as sunspots are manifestations of the activity of the Sun. However, it is the plasma ejected during these periods which interacts directly with the Earth's environment. This plasma comes mainly from coronal holes and gives rise to geomagnetic disturbances such as aurorae (Crooker and Siscoe, 1986). Although most interplanetary shocks are associated to either flares or prominences (see, for instance, Cane, 1988, and references therein), it has also been suggested, that the anomalous solar activity which
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