FURTHER-STUDIES ON POSSIBLE VOLCANIC SIGNAL TO THE OZONE-LAYER

This paper provides a new look at the spatial and temporal distributio n of monthly mean residuals of the global ozone field following the tw o large volcanic eruptions of El Chichon and Pinatubo. The residuals h ave been calculated after careful removal of the components of known o scillations from the monthly mean total ozone records. The removal eli minated not only the well-established Quasi Biennial Oscillation but a lso the robust pattern of all El Nino/Southern Oscillation events acti ve during the period of study. These residuals are composed by a ''cli matic noise'' term plus a possible volcanic signal whose amplitude is in some agreement with model calculations particularly over low and mi ddle latitudes following the recent Pinatubo eruption. However, this a nalysis shows no ozone deficiency following El Chichon over the southe rn hemisphere and this result can be explained by the prevailing winds in the lower stratosphere in the post-El Chichon period as described in the text. Quantitatively speaking, the magnitude of the observed oz one deficiency which can be attributed to the volcanic effect is small er than reported earlier either from theory or observations, and range s between 2 and 4% at the equatorial latitudes up to about 5% over the middle and high latitudes, including the noise term, and lasting for a period of months after the eruption. These deficiencies are also lar ger than the anticipated error caused by the aerosol-contaminated radi ances, as reported by other scientists. The present results, although not precluding a transient volcanic component following large volcanic eruptions in the ozone records, do show, however, that our understand ing of the physical mechanisms involved is probably still incomplete.