VOLCANIC AEROSOL PERTURBATIONS AND STRONG EL-NINO EVENTS - NO GENERALCORRELATION

We test the hypothesis that El Nino/Southern Oscillation (ENSO) events are caused or enhanced by volcanic aerosol perturbations using two me thods: 1) A case-by-case comparison of the 16 strongest El Nino events of the last 150 years with the characteristics of the largest concurr ent volcanic events, and 2) Comparison of the timing of strong El Nino events and the independently determined record of stratospheric optic al depth (2) perturbations. Many eruptions that occurred near times of strong El Nino years produced small amounts of stratospheric aerosols , in many cases the relative timing of the two events argues against t riggering. The correlation of 4 of 11 peaks in global stratospheric op tical depth (tau greater than or equal to 0.025) within 3 years of str ong El Nino events over the last 150 years is what would be expected b y chance. Moreover, five strong El Ninos occurred between 1915 and 196 0, when the stratosphere was largely free of volcanic aerosols. Of the three strongest tropical volcanic aerosol perturbations that coincide d with or were followed by strong El Ninos in the period studied (Krak atau in 1883, El Chichon in 1982, and Pinatubo in 1991), the two moder n ones occurred after the earliest SST warming of the El Nino events. The coincidence of these two phenomena indicates no causative relation ship.