The influence of the southern oscillation and volcanic eruptions on temperature in the tropical troposphere

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Abstract
Upper‐air data for a network of tropical stations have been used to create seasonal and annual time‐series of 850‐500 mb and 500‐200 mb thickness for the zone 20°N–20°S for 1950‐1983.Linear regressions of thickness in each layer against a Southern Oscillation index show that in the northern winter about half the interannual variance of thickness is predicted by the Southern Oscillation index two seasons earlier. Similar but weaker results hold for the other seasons. Low Southern Oscillation index, implying low pressure in the southern tropical mid‐Pacific, is followed by a warm tropical troposphere.The residuals of thickness after the regressions against the Southern Oscillation index were examined for evidence of the effects of major volcanic eruptions. The cooling in 1964‐1965 cannot be ascribed unambiguously to the March 1963 eruption of Agung, and there has been no significant cooling in the two years following the April 1982 eruption of El Chichón.