The 1985 Southern Hemisphere mid-latitude total column ozone anomaly

[摘要] One of the most significant events in the evolution of the ozone layer over southernmid-latitudes since the late 1970s was the large decrease observed in 1985. This eventremains unexplained and a detailed investigation of the mechanisms responsible for theevent has not previously been undertaken. In this study, the 1985 Southern Hemisphere mid-latitudetotal column ozone anomaly is analyzed in detail based on observed daily total column ozone fields,stratospheric dynamical fields, and calculated diagnostics of stratospheric mixing. The 1985 anomalyappears to result from a combination of (i) an anomaly in the meridional circulation resulting from thewesterly phase of the equatorial quasi-biennial oscillation (QBO), (ii) weaker transport of ozone fromits tropical mid-stratosphere source across the sub-tropical barrier to mid-latitudes related to theparticular phasing of the QBO with respect to the annual cycle, and (iii) a solar cycle inducedreduction in ozone. Similar QBO and solar cycle influences prevailed in 1997 and 2006 when againtotal column ozone was found to be suppressed over southern mid-latitudes. The results based onobservations are compared and contrasted with analyses of ozone and dynamical fields from theECHAM4.L39(DLR)/CHEM coupled chemistry-climate model (hereafter referred to as E39C). Equatorialwinds in the E39C model are nudged towards observed winds between 10° S and 10° Nand the ability of this model to produce an ozone anomaly in 1985, similar to thatobserved, confirms the role of the QBO in effecting the anomaly.

[学科分类] 大气科学